INTERACTION OF NEUTRONS WITH NUCLEI

V. N. Kondrat’ev

INTRODUCTION

As is known, nuclear reactions involving charged particles—protons and $\alpha$-particles—are especially frequent in the case of light nuclei, whose Coulomb field is not an insurmountable obstacle to the penetration of a charged particle into the nucleus even at a comparatively small particle energy. In the case of heavy nuclei, in order to overcome Coulomb repulsion the charged particle must possess considerable energy. Therefore reactions of protons and $\alpha$-particles with heavy nuclei are comparatively rare and proceed, practically, exclusively by the mechanism of resonant penetration of the charged particle into the nucleus—a mechanism that also plays a large role in the case of light nuclei.

The yield of these reactions is determined by the probability that the particle will penetrate through the potential barrier of the nucleus. This probability can be calculated theoretically1 and proves to be very sensitive to the energy of the exciting particle. Let us note that in the case of deuteron reactions accompanied by the ejection of a proton and having a comparatively large probability, another mechanism is also possible, first proposed by Oppenheimer and Phillips2. According to this mechanism, because of the comparatively low dissociation energy of the deuteron, even when the deuteron has not fully penetrated into the nucleus, under the influence of the latter’s electric field it splits into a proton and a neutron; in this process the proton is repelled, while the neutron is captured by the nucleus, as a result of which a heavier isotope of the initial element is formed.

In contrast to charged particles, neutrons approach the nucleus without hindrance, which accounts for the great prevalence of nuclear reactions involving a neutron and observed equally often both in the case of light and in the case of heavy nuclei. For this same reason, a large number of exothermic nuclear reactions take place under the action of thermal neutrons, i.e., neutrons that are in thermal equilibrium with the surrounding bodies.

V. N. KONDRAT’EV

Alongside interactions leading to the transformation of some nuclei into others, in collisions of neutrons with nuclei there are observed cases of interaction in which the nature of the colliding particles after the collision remains unchanged. These cases are known as neutron scattering. The simplest of them is elastic scattering—a phenomenon analogous to the impact of elastic spheres. In this case, according to the laws of conservation of energy and momentum, the following relation holds between the energy of the neutron after impact, \(E_n\), and its initial energy \(E_n^0\) (the nucleus before impact is assumed to be at rest):

\[ \frac{E_n}{E_n^0} = \frac{ (m^2-m_n^2)+2m_n^2\cos^2\vartheta +2m_n\cos\vartheta\sqrt{(m^2-m_n^2)+m_n^2\cos^2\vartheta} }{ (m+m_n)^2 }, \tag{1} \]

where \(m\) and \(m_n\) are respectively the masses of the nucleus and the neutron, and \(\vartheta\) is the scattering angle. The energy of the nucleus after impact \(E\) (the recoil nucleus or atom) and the quantity \(E_n^0\) are related by

\[ \frac{E}{E_n^0} = 2\, \frac{ (m+m_n)-m_n\cos^2\vartheta -\cos\vartheta\sqrt{(m^2-m_n^2)+m_n^2\cos^2\vartheta} }{ (m+m_n)^2 }\,m_n . \tag{2} \]

In the case of a central impact \((\vartheta=\pi)\), from (1) and (2) we obtain

\[ \frac{E_n}{E_n^0} = \left(\frac{m-m_n}{m+m_n}\right)^2 . \tag{3} \]

and

\[ \frac{E}{E_n^0} = \frac{4mm_n}{(m+m_n)^2}. \tag{4} \]

Let us note that equality (4) also expresses the energy loss of the elastically scattered neutron in a central impact. The average energy loss will evidently be equal to\(^3\)

\[ \frac{\overline{\Delta E_n}}{E_n^0} = \frac{2mm_n}{(m+m_n)^2}. \tag{5} \]

In contrast to elastic scattering, in inelastic scattering some part of the neutron energy is transformed into the internal energy of the bombarded nucleus, which as a result of the collision is found to be in an excited state. As a rule, such an excited nucleus proves to be \(\gamma\)-active. Denoting the excitation energy of the nucleus by \(E_r\), from the conservation laws we obtain the following expression for the loss of neutron energy in an inelastic collision:

\[ \frac{\Delta E_n}{E_n} = \frac{2}{(m+m_n)^2} \left\{ (m+m_n) \left( 1+\frac{m}{2m_n}\frac{E_r}{E_n^0} \right) -m_n\cos^2\vartheta -\cos\vartheta \sqrt{ (m^2-m_n^2)+m_n^2\cos^2\vartheta -m(m+m_n)\frac{E_r}{E_n^0} } \right\}m_n . \tag{6} \]

which, in the case of a central collision, becomes

\[ \frac{\Delta E_n}{E_n^0} = \frac{2mm_n}{(m+m_n)^2} \left( 1+\frac{m+m_n}{2m_n}\frac{E_r}{E_n^0} + \sqrt{\,1-\frac{m+m_n}{m}\frac{E_r}{E_n^0}\,} \right). \tag{7} \]

From a comparison of expressions (4) and (7) it is evident that the excitation of a nucleus occurring in inelastic scattering of neutrons substantially increases the energy losses in the scattering of neutrons by nuclei. These losses are relatively large especially in the case of heavy nuclei, since here, owing to the small value of the ratio of the neutron and nuclear masses, the losses as a result of elastic scattering (4) are comparatively negligible, while the presence of a large number of excitation levels of the nucleus makes inelastic scattering a very probable process. Therefore the slowing down of fast neutrons in heavy materials must, in the main, be due to inelastic scattering.

In contrast to this, the slowing down of neutrons in light materials is practically connected with elastic scattering. Such, in particular, is the slowing down of neutrons in hydrogen-containing substances (water, paraffin). As follows from formula (5), hydrogen is the most effective moderator (in view of \(m \simeq m_n\)). As a result of \(N\) collisions with protons the mean value of the neutron energy proves to be equal to the fraction \(1/2^N\) of its initial energy.\(^4\)

It follows from this, in particular, that, for example, a neutron whose initial energy is several MeV comes into thermal equilibrium with the surrounding bodies after \(\sim 20\) collisions with protons.

Let us proceed to consider the interaction of a neutron with a nucleus, which is a nuclear reaction of one type or another. The simplest of these reactions is the capture of a neutron by a nucleus, as a result of which a heavier isotope of the given element is formed. A reaction of this type (capture) may be represented by the formula

\[ Z^A + n^1 \longrightarrow Z^{A+1}. \tag{8} \]

Here \(A\) denotes the mass (atomic) number of the given element and \(n\) the neutron. The isotope with a mass number one unit greater than the mass number of the original isotope, arising as a result of capture of a neutron by the latter, may be either a stable isotope of the given element or radioactive (\(\gamma\) or \(\beta\)). Owing to the immeasurably greater ease of detecting radioactive isotopes, in almost all studied cases of capture the newly arising isotope proves to be radioactive. Numerous examples of reactions of this type may be found in Seaborg’s well-known tables.\(^5\) However, irrespective of the ease of detecting radioactive isotopes, it must be said that, owing to the considerable exothermicity of capture reactions, characterized by a thermal effect of several MeV, the formation of excited (i.e. radioactive) nuclei, especially in the case of

heavy elements with their large number of excitation levels seems highly probable.

An example of a capture reaction resulting in the formation of a stable isotope is the capture of a neutron by a proton, leading to the formation of deuterium

\[ \mathrm{H}_1^1 + n_0^1 \longrightarrow \mathrm{D}_1^2 . \tag{9} \]

In all cases the stability of the newly arising isotope (whether stable or radioactive—metastable) is achieved by the emission, at the moment of capture, of a \(\gamma\)-quantum. Therefore neutron capture is a reaction of the type \((n,\gamma)\). The magnitude of the emitted \(\gamma\)-quantum \((\gamma)\) may be obtained from the equality

\[ E_n + c^2\Delta = E_r + E + \gamma, \tag{10} \]

which expresses the law of conservation of energy. Here \(E_n\) is the energy of the neutron, \(\Delta\) is the mass defect, \(c\) is the speed of light, \(E_r\) is the excitation energy of the new nucleus (the value \(E_r\) may be equal to zero), and \(E\) is its kinetic energy. We note that the \(\gamma\)-spectra accompanying the capture of neutrons by nuclei usually (especially in the case of heavy nuclei) prove to be sufficiently complex. It follows from this that, in these cases, the nuclei arising upon neutron capture are at various degrees of excitation, or else their excitation energy is emitted in the form of several successive photons.

Let us next consider nuclear reactions accompanied by the emission from the nucleus of a charged particle—an \(\alpha\)-particle \((\alpha)\) or a proton \((p)\), i.e., reactions of the types \((n,\alpha)\) and \((n,p)\).

These reactions are represented by the formulas

\[ Z^A + n^1 \longrightarrow (Z-2)^{A-3} + \mathrm{He}^4 \tag{11} \]

and

\[ Z^A + n^1 \longrightarrow (Z-1)^A + \mathrm{H}^1 . \tag{12} \]

From a comparison of the masses of the initial and final particles it follows that, with a small number of exceptions, reactions of both types are endothermic and, consequently, must occur predominantly in the case of fast neutrons. Further, owing to the presence of a potential barrier for charged particles, the \(\alpha\)-particles and protons arising as a result of reactions (11) and (12), irrespective of the sign of the energy effect of the reaction, always possess a greater or lesser kinetic energy; this likewise implies a greater probability of the reaction for fast neutrons. For the same reason, the reactions under consideration should be most probable in the case of light nuclei with their comparatively low potential barrier. All these conclusions are confirmed by experiment.^6

The nuclei arising as a result of the reactions under consideration, as well as the nuclei arising in the \((n,\gamma)\) reaction, have, in comparison with the initial nuclei, a greater number of neutrons, accounting for

on one proton and therefore, as a rule, are electron-active, i.e. undergo a further transformation of the type

\[ Z^A \longrightarrow (Z+1)^A + e^- . \tag{13} \]

Along with the \((n,\alpha)\) reactions of type (11), reactions are known in which several \(\alpha\)-particles arise. Such, for example, are the reactions

\[ \mathrm{B}^{10}+n^1 \longrightarrow \mathrm{H}^3+2\mathrm{He}^4 \]

and

\[ \mathrm{C}^{12}+n^1 \longrightarrow 3\mathrm{He}^4+n^1, \]

of which the latter may also be regarded as an inelastic collision of a neutron with a nucleus.

Apparently close in mechanism to this reaction is the \((n,2n)\) reaction, i.e. the reaction corresponding to the formula

\[ Z^A+n^1 \longrightarrow Z^{A-1}+2n^1 . \tag{14} \]

Here the neutron, without being captured by the nucleus, imparts to it energy sufficient for the liberation of a second neutron. In view of the considerable binding energy of the neutron in the nucleus (about 8 MeV in light nuclei and about 6 MeV in heavy ones), reaction (14) is strongly endothermic and is therefore possible only in the case of fast neutrons. Since, as a result of this reaction, nuclei arise with a smaller number of neutrons than the original nuclei, its products, as a rule, prove to be positron-active, i.e. undergo a transformation of the type

\[ Z^A \longrightarrow (Z-1)^A + e^+ , \tag{15} \]

although electron activity here is not rare.

Let us add that there are experimental grounds for assuming, in a number of elements (Sc, F, Cu), also the reaction \((n,3n)\), i.e. the ejection by a fast neutron not of one, but of two neutrons from the nucleus[^6].

Let us also note that the products of the \((n,2n)\) reaction must evidently be the same as the products of the photoreaction \((\gamma,n)\), i.e. the ejection of a neutron from a nucleus by a \(\gamma\)-quantum.

Finally, the last, particularly important nuclear reaction occurring with the participation of a neutron is the reaction of fission, as a result of which two heavy particles (fragments) and several neutrons (fission neutrons) arise.

The fission reaction may be represented by the following formula:

\[ Z^A+n^1 \longrightarrow Z_1^{A_1}+Z_2^{A_2}+\nu n^1, \tag{16} \]

where

\[ Z_1+Z_2=Z \]

and

\[ A_1+A_2+(\nu-1)=A. \]

As is known, only the heaviest nuclei—Th, Pa, U, Np, Pu and, apparently, all other transuranium elements—possess the capacity for fission. The fission of uranium has been studied in the greatest detail. In this case the existence has been established of two groups of fission fragments[^7]: lighter ones with masses \(A_1\), lying in the range from 80 to 115, with mean value 97, and heavier ones with masses \(A_2\) from 125 to 160, with mean value 142. The fission fragments contain an excess number of neutrons and therefore are electron-active, undergoing a whole series of successive transformations. Some of the initially produced fragments are also capable of emitting neutrons (delayed neutrons). The number of fission neutrons \(\nu\) in the case of uranium[^8], apparently, on average somewhat exceeds 2.

In all fission reactions a tremendous energy is liberated (about 160 MeV), from which it follows that these reactions are highly exothermic. However, only in the case of the light isotope of uranium—\(U^{235}\) (and in the case of Pu)—is fission observed upon interaction with neutrons of any velocity (down to thermal ones). In the remaining cases (\(U^{238}\), Th, Pa and Np), fission occurs only upon interaction with fast neutrons, which indicates the existence of a certain excitation threshold for the fission reaction in these cases.

Let us add that recently cases have been discovered of fission into several charged particles, when, alongside two heavy fission fragments, one or two light particles were observed, or one light particle together with three heavy ones[^9]. These cases, however, are relatively rare.

The effectiveness of a nuclear reaction is characterized by a certain probability that is a function of the energy or velocity of the neutron. This probability is customarily expressed through the reaction cross section \(\sigma\), which is defined in the following way. Denoting the density of the neutron flux, i.e. the number of neutrons incident each second on \(1\ \mathrm{cm}^2\) of the surface of the reagent, by \(q\), the concentration of the latter, i.e. the number of nuclei in \(1\ \mathrm{cm}^3\), by \(C\), and the thickness of the reacting layer by \(dl\), for the number of transformations \(dq\) in one second (the rate of the nuclear reaction) we shall have

\[ -dq=\sigma Cq\,dl . \tag{17} \]

It follows from this equality that in the absolute system of units the reaction cross section \(\sigma\) must be expressed in \(\mathrm{cm}^2\). Since \(\sigma\) most often has an order of magnitude \(10^{-24}\), it is convenient to express it in units \(10^{24}\) times smaller than \(1\ \mathrm{cm}^2\).

In accordance with the nuclear process to which the given cross section corresponds, we shall have the scattering cross section \(\sigma_{\mathrm{scatt}}\), composed of the cross sections for elastic \((\sigma_{\mathrm{el}})\) and inelastic \((\sigma_{\mathrm{inel}})\) scattering,

\[ \sigma_{\mathrm{scatt}}=\sigma_{\mathrm{el}}+\sigma_{\mathrm{inel}}, \tag{18} \]

the capture cross section \(\sigma_{\mathrm{capt}}\), the cross section for the reaction of nuclear fission \(\sigma_{\mathrm{f}}\), po-

taking to mean by this reaction one of the following reactions: \((n,\alpha)\), \((n,p)\), or \((n,2n)\), and the fission cross section \(\sigma_{\mathrm{f}}\). The sum of these cross sections

\[ \sigma = \sigma_{\mathrm{scatt}} + \sigma_{\mathrm{capt}} + \sigma_{\mathrm{p}} + \sigma_{\mathrm{f}} \tag{19} \]

is called the total cross section. As we shall see below, very often \(\sigma=\sigma_{\mathrm{scatt}}\) \((\sigma_{\mathrm{capt}}=\sigma_{\mathrm{p}}=\sigma_{\mathrm{f}}=0)\) or \(\sigma=\sigma_{\mathrm{capt}}\) \((\sigma_{\mathrm{p}}=\sigma_{\mathrm{f}}=0,\ \sigma_{\mathrm{scatt}}\approx 0)\). Cross sections are determined experimentally, but with greater or lesser accuracy they can also be calculated theoretically, especially their dependence on neutron velocity. In what follows we shall first of all dwell on the theory of cross sections, which is essentially the theory of nuclear reactions.

I. THEORY OF NUCLEAR REACTIONS

The modern theory of nuclear reactions proceeds from Bohr’s fundamental ideas\(^{10}\), which treat every nuclear process as a many-body problem. The basis for this is the rapid decrease of nuclear forces with distance, as a consequence of which an external particle—in particular a neutron—which has entered the nucleus or has found itself near its surface cannot interact with any single particle making up the nucleus: its interaction extends over several nuclear particles, and the magnitude of this interaction must be of the same order as the interaction among the latter, since the range of nuclear forces is of the same order of magnitude as the mean distance between nuclear particles. As a result, the energy of a neutron that has entered the nucleus is rapidly distributed among the nuclear particles; there arises a compound nucleus, possessing a greater or lesser degree of stability, characterized by some mean lifetime \(\tau\). The magnitude of \(\tau\) is determined by the probability of such a redistribution of energy in the compound nucleus, as a result of which one or another nuclear process becomes possible. At the same time, depending on the character of this redistribution of energy and on its concentration on one or another particle, this particle may fly out of the nucleus. If this particle proves to be a neutron, we shall be dealing with neutron scattering, which will be elastic scattering in the case when the energy acquired by the neutron is equal to the energy of the bombarding neutron. Such a case, generally speaking, must be less probable than the case in which the neutron receives a different, smaller energy; then the scattering will be inelastic. In this latter case, an energy equal to the difference between the energies of the bombarding neutron and of the neutron emerging from the compound nucleus remains in the nucleus in the form of its excitation energy. Thus, the Bohr picture of the compound nucleus leads to the conclusion that inelastic scattering must be more probable than elastic scattering—at least in the case of heavy nuclei with their large number of energy levels and large number of nuclear particles.

If the energy in the compound nucleus proves to be concentrated on a proton or an \(\alpha\)-particle, then as a result the reaction \((n,p)\) or \((n,\alpha)\) becomes possible. In exactly the same way, a redistribution of energy corresponding to the formation of an excited compound nucleus makes possible the process of capture accompanied by emission of a \(\gamma\)-quantum, which leads to stabilization of the compound nucleus.

Thus, according to Bohr, every nuclear process must be represented as the following double transition: initial nucleus \(+\) neutron \(\xrightarrow{\text{I}}\) compound nucleus \(\xrightarrow{\text{II}}\) final nucleus \(+\) emitted particle (in particular, a photon).

The lifetime of the compound nucleus arising as a result of transition I is, generally speaking, sufficiently long for it to be able to possess definite “virtual” or “resonance” energy levels; the positions of these levels and the properties of the corresponding metastable states of the compound nucleus determine the cross sections of all nuclear reactions. Therefore, in the modern quantum-mechanical treatment of a nuclear reaction, the latter is considered as the transition of the neutron from its initial state to various levels of the compound nucleus (I), followed by a transition (II) to a new state, which is the final state of the reacting system. In this case, if the final state of the neutron is the same as its initial state, we have a process of elastic scattering. If the final and initial states of the neutron are different, we have inelastic scattering, capture, or some other nuclear reaction. From the foregoing it is clear that a nuclear reaction, considered as a quantum-mechanical process, has a great analogy with the processes of scattering and absorption of light quanta. This analogy is manifested, in particular, in the fact that for the cross sections one obtains formulas reminiscent of the optical dispersion formula. According to these formulas, resonance effects must play an exceptionally important role in nuclear reactions—a fact already established experimentally in the first studies of the interaction of \(\alpha\)-particles and protons with nuclei, which revealed maxima of scattering and disintegration at definite values of the energy of the bombarding particles.

In the wave theory of nuclear reactions, a monochromatic beam of neutrons is represented by a wave to which there corresponds the wave number

\[ k=\frac{2\pi}{\lambda}, \tag{20} \]

where \(\lambda\) is the de Broglie wavelength, related to the velocity and energy of the neutron by the relation

\[ \lambda=\frac{h}{mv}=\frac{h}{\sqrt{2mE_n}}. \tag{21} \]

INTERACTION OF NEUTRONS WITH NUCLEI

(\(m\) — the mass of the neutron, \(v\) — its velocity). This wave, in the general case, is a superposition of partial waves characterized by the quantum number \(l = 0, 1, 2, \ldots\) (\(s\)-, \(p\)-, \(d\)-, ... waves), which determines the angular momentum of the neutrons

\[ mvr=\frac{h}{2\pi}l=\hbar l . \tag{22} \]

From formulas (21) and (22) it follows that the distance \(r\) at which the neutron passes from the nucleus is equal to \(r=\frac{\lambda}{2\pi}l\). Since \(\lambda\), increasing as \(E_n\) decreases, already at \(E_n<0.5\) MeV becomes greater than the nuclear radius, it follows from this relation that only fast neutrons can enter the nucleus for \(l>0\). Therefore partial waves with \(l>0\) have an essential significance for nuclear processes only in the case of fast neutrons; a beam of slow neutrons, however, is represented by a wave with \(l=0\) (an \(s\)-wave).

In this latter case (\(l=0\)) the process is described by the spherically symmetric part of the neutron wave function, which is a solution of the Schrödinger equation

\[ \frac{\hbar^2}{2m}\frac{d^2\varphi}{dr^2}+\left[E-V(r)\right]\varphi=0, \tag{23} \]

where \(\varphi=r\psi\), \(E\) is the kinetic and \(V(r)\) the potential energy of the neutron (\(r\) is the distance of the neutron from the nucleus). For \(r>a\) (\(a\) is the nuclear radius) \(V=0\), and equation (23) becomes

\[ \frac{d^2\varphi}{dr^2}+k^2\varphi=0 \tag{24} \]

(in view of \(k^2=\frac{2mE}{\hbar^2}\)). The solution of the latter equation may be written in the following form:

\[ \varphi=r\psi=e^{-ikr}+\eta e^{ikr}. \tag{25} \]

In the absence of absorption \(|\eta|^2=1\), in the presence of absorption \(|\eta|^2<1\). At the surface of the nucleus the function (25) passes into the wave function corresponding to the interior of the nucleus and constituting the solution of a complicated many-body problem. This solution, obtained by a number of authors \(^{11}\), leads to “dispersion formulas” for cross sections corresponding to various nuclear processes.

Below we give a simplified derivation of these formulas according to one of the recent works of Weisskopf and collaborators \(^{12}\). In the case of fast neutrons, for which \(\frac{\lambda}{2\pi}\ll a\), the maximum cross section is equal to \(\sigma_0=\pi a^2\). As the neutron energy decreases, the quantity \(\sigma_0\) increases, approaching \(\sigma_0=\frac{\lambda^2}{4\pi}\) for \(\frac{\lambda}{2\pi}\gg a\). The actual value

the cross section can be defined as the maximal one multiplied by the probability of the given process \(w\), i.e.

\[ \sigma=\sigma_0 w . \tag{26} \]

By the definition of the quantity \(\eta\), the probability of absorption is obviously equal to \(1-|\eta|^2\), and, consequently, the absorption cross section is written in the form

\[ \sigma_{\mathrm{abs}}=\sigma_0(1-|\eta|^2). \tag{27} \]

Let us recall that by absorption here one means one of the following processes: inelastic scattering, capture, splitting, fission.

Next, the probability of elastic scattering can be calculated as the ratio of the squares of the amplitudes of the scattered and incident waves. Taking from the function \(\varphi\) (25) the part corresponding to the scattered wave, subtracting from (25) the wave function of a plane wave \(e^{-ikr}+e^{ikr}\), we find that

\[ \varphi_{\mathrm{sc}}=(1+\eta)e^{ikr}. \]

Consequently, the probability of elastic scattering will be equal to \(|1+\eta|^2\), and for the cross section \(\sigma_{\mathrm{el}}\) we obtain

\[ \sigma_{\mathrm{el}}=\sigma_0|1+\eta|^2 . \tag{28} \]

Introducing, further, the function

\[ f(E)=a\frac{\varphi'_a}{\varphi_a}=f_0-ih, \tag{29} \]

where \(\varphi'_a\) and \(\varphi_a\) are the values of \(\dfrac{d\varphi}{dr}\) and \(\varphi\) at \(r=a\), \([h(>0)\) and \(f_0\) are real quantities], from (25) and (29) we find

\[ \eta=\frac{(x+h)-if_0}{(x+h)+if_0}e^{-2ix}, \tag{30} \]

where \(x=ka\). Substituting this expression for \(\eta\) into formulas (27) and (28), after simple transformations we obtain

\[ \sigma_{\mathrm{abs}}=4\sigma_0\frac{xh}{(x+h)^2+f_0^2} \tag{31} \]

and

\[ \sigma_{\mathrm{el}}=4\sigma_0\left|\frac{x}{i(x+h)-f_0}+e^{ix}\sin x\right|^2 . \tag{32} \]

From (31) and (32) it is seen that resonance occurs when \(f_0=0\). Therefore those energy values \(E\) for which the quantity \(f_0\) vanishes may be called the resonance energy of the compound nucleus \(E_r\). Consequently,

\[ f_0(E_r)=0. \]

Near the resonance we set

$$ f_0(E)=\left(\frac{df_0}{dE}\right)_{E_r}(E-E_r) \tag{33} $$

and, introducing the following abbreviated notation,

$$ \Gamma_n^{(r)}=-2x:\left(\frac{df_0}{dE}\right)_{E_r} \tag{34} $$

and

$$ \Gamma_a^{(r)}=-2h:\left(\frac{df_0}{dE}\right)_{E_r}, \tag{35} $$

by substituting (33), (34), and (35) into (31) and (32), we obtain

$$ \sigma_{\mathrm{abs}}=\sigma_0 \frac{\Gamma_n^{(r)}\Gamma_a^{(r)}} {(E-E_r)^2+\frac{1}{4}\left(\Gamma_n^{(r)}+\Gamma_a^{(r)}\right)^2} \tag{36} $$

and

$$ \sigma_{\mathrm{el}}=4\sigma_0 \left| \frac{-\frac{1}{2}\Gamma_n^{(r)}} {(E-E_r)+\frac{i}{2}\left(\Gamma_n^{(r)}+\Gamma_a^{(r)}\right)} +e^{ix}\sin x \right|^2 . \tag{37} $$

Comparing formulas (36) and (37) with the optical dispersion formulas, and also taking into account the circumstance that the quantum-mechanical theory both of the phenomena of absorption and scattering of light and of nuclear processes is based on analogous concepts of quantum transitions in the transition system, the quantities \(\Gamma\) entering these formulas can be interpreted as quantities proportional to the probabilities of quantum transitions: \(\Gamma_n^{(r)}\) is the probability of the transition corresponding to the decay of the compound nucleus with emission of a neutron, and \(\Gamma_a^{(r)}\) is the probability of the transition accompanied by emission of a particle \(a\) (in particular, a \(\gamma\)-quantum). In essence, the quantity \(\Gamma_n^{(r)}\) represents that part of the width of the level \(E_r\) which corresponds to neutron scattering, while \(\Gamma_a^{(r)}\) is the width corresponding to neutron absorption (capture, scattering, fission of the nucleus). The quantity \(\Gamma^{(r)}=\Gamma_n^{(r)}+\Gamma_a^{(r)}\), obviously, represents the total width of the level \(E_r\). The term \(e^{ix}\sin x\) in formula (37) determines the so-called potential scattering, caused by the finite dimensions of the nucleus, while the term \(-\frac{1}{2}\Gamma_n^{(r)}:\left[(E-E_r)+\frac{i}{2}\Gamma^{(r)}\right]\) is the resonance effect. This effect manifests itself in the fact that, at a neutron energy equal to \(E_r\), the cross section of one or another nuclear process has a more or less sharp maximum; the maximum value of the cross section very often exceeds the corresponding values at \(E\ne E_r\) by tens, hundreds, and even thousands of times (see below).

As can be concluded from the preceding derivation of the “dispersion formulas” (36) and (37), they should be valid only in the immediate vicinity of the resonance point \(E=E_r\) [in view of the assumption

(33)]. However, experience shows (see below) that in reality these formulas describe the behavior of the quantity \(\sigma\) as a function of the neutron energy sufficiently well over a considerable energy interval—the more so, the farther the level \(E_r\) is from neighboring resonance levels. In the more general case, when these levels are situated rather close to one another, the nuclear reaction is associated with virtual transitions to several different levels of the compound nucleus. In this case the corresponding more general formulas for the cross sections can be obtained, which have the form

\[ \sigma_{\mathrm{capt}}=\sigma_0\left| \sum_r \frac{\left(\Gamma_n^{(r)}\Gamma_a^{(r)}\right)^{1/2}} {(E-E_r)+\dfrac{i}{2}\Gamma^{(r)}} \right|^2, \tag{38} \]

\[ \sigma_{\mathrm{el}}=4\pi g_0 \left| \frac{1}{2}\sum_r \frac{\Gamma_n^{(r)}} {(E-E_r)+\dfrac{i}{2}\Gamma^{(r)}} +e^{ix}\sin x \right|^2. \tag{39} \]

However, these formulas too are not yet general: they are valid only in the case when the levels of the compound nucleus are not degenerate. In the case of degenerate levels, the expressions for the cross sections contain still further quantum numbers that determine the quantum states of the compound nucleus. In addition, as in the case of formulas (36) and (37), the angular momentum of the neutrons is assumed to be zero \((l=0)\). For \(l>0\), a factor \(2l+1\) enters into the expressions for the cross sections. Let us add also that virtual transitions in the compound nucleus obey definite selection rules, which substantially influence the probabilities of these transitions.

In what follows we shall consider some of those features of the cross sections in their dependence on neutron energy which follow from the “dispersion formulas.” In doing so it is convenient to consider separately nuclear processes involving slow and fast neutrons.

Slow neutrons are customarily understood to mean neutrons with energies from several thousand eV down to energies of the order of \(kT\) (hundredths of an eV, thermal neutrons). In the region of slow neutrons, the resonance levels of the nucleus (especially in the case of light nuclei) are not so closely spaced; for this reason, often over a considerable energy interval the role of the terms corresponding to high energy levels of the compound nucleus proves to be negligible, and the behavior of the cross section as a function of energy is described sufficiently well by the simple one-term formulas (36) and (37). As was already indicated above, in the case of slow neutrons the quantity \(\sigma_0\) is expressed by the formula

\[ \sigma_0=\frac{\lambda^2}{4\pi}. \]

The number \(l\) in this case is equal to zero.

From formulas (36) and (37) it is first of all evident that the resonance effect is most sharply expressed only in the case of processes connected with ...

with neutron absorption (\(\sigma_{\mathrm{abs}}\)), since in elastic scattering (\(\sigma_{\mathrm{el}}\)), owing to the presence of potential scattering, the dependence of the cross section on the quantity \(E-E_r\) is less sharp. This conclusion is in fact confirmed by experimental data. In particular, the phenomenon of resonance itself was discovered precisely as a result of studying the processes of neutron absorption—capture reactions (resonance capture), where it is expressed especially vividly. Further, from formula (36), also in complete agreement with experiment, it follows that

Fig. 1. Total cross section of cadmium (according to Zinn).

the resonance effect must be especially sharp in the case of slow neutrons. Indeed, in this case, at the resonance point \((E=E_r)\), the quantity \(\sigma_{\mathrm{abs}}\) must be of the order of (for \(\Gamma_n^{(r)}\) not differing greatly from \(\Gamma^{(r)}\))

\[ \sigma_0=\frac{\lambda^2}{4\pi}\gg \pi a^2, \]

whence arise those large values of the quantity \(\sigma_{\mathrm{abs}}\) which are characteristic of the resonance effect.

To illustrate the resonance effect, we give (Fig. 1) the results of measuring the total cross section of cadmium for slow neutrons\(^{13}\). The curve in Fig. 1 is constructed according to the formula

\[ \sigma=\sigma_r\frac{\Gamma^2\left(\dfrac{E_r}{E}\right)^{\frac12}}{4(E-E_r)^2+\Gamma^2} \tag{40} \]

for the following values of the constants entering into it: \(E_r=0.180\,\mathrm{eV}\), \(\Gamma=0.122\,\mathrm{eV}\), and \(\sigma_r=7800\). Formula (40) can be readily obtained from formulas (36) and (37). Indeed, neglecting the potential

scattering, from these formulas we obtain for \(\sigma=\sigma_{\mathrm{abs}}+\sigma_{\mathrm{sc}}\) the expression

\[ \sigma=\sigma_0\frac{4\Gamma\Gamma_n}{4(E-E_r)^2+\Gamma^2}. \tag{41} \]

Further, in view of the absence of an explicit dependence of the function \(f_0\), as well as of its derivative, on the quantity \(x=ka=\dfrac{2\pi a}{\lambda}\), we have \(\Gamma_n\sim\dfrac{2\pi}{\lambda}\) (34) and, consequently, \(\sigma_0\Gamma_n\sim\dfrac{\lambda}{2\pi}\sim E^{-1/2}\). Thus, introducing the quantity \(\sigma_r\), which represents the cross section at the resonance point \((E=E_r)\), we also arrive at formula (40). Let us add that the maximum value—

Fig. 2. Complete cross section of iridium (after Sturm).

—of the cross section \(\sigma=\sigma_r=7800\) is, for natural cadmium, a certain average value. Since in reality \(^{14}\) the resonance level \(0.180\) belongs to the isotope cadmium 113, contained in natural cadmium in the amount of \(12.3\%\), then in the calculation for this isotope we obtain \(\sigma_r=63400\).

In Fig. 2 are shown the measured values of the quantity \(\sigma\sqrt{E}\) (\(E\) in eV) as a function of the neutron energy for iridium \(^{15}\), which in the interval \(0.3\)--\(10\) eV has three resonance levels: \(E_r=0.635\) eV, \(1.35\) eV, and \(6.0\) eV. To these levels correspond the following values of the quantity \(\sigma_r\): \(543\), \(612\), and \(\sim 95\).

Further, as is evident from formula (40), for \(E\ll E_r\), i.e. in the region of small energies, the cross section \(\sigma\) must be inversely proportional to \(E^{1/2}\sim v\) (the neutron velocity), which in a number of cases was

has been established experimentally for a more or less broad interval of neutron energies. In particular, the law

\[ \sigma \sim \frac{1}{v} \tag{42} \]

in the case of iridium is clearly manifested in Fig. 2 for energy values \(E < 0.2\ \mathrm{eV}\), when the quantity \(\sigma \sqrt{E} \sim \sigma v\) retains a practically constant value. It must be noted, however, that the simple law (42) is observed comparatively rarely. More often, in the region of small energy values there is a linear dependence of \(\sigma\) on \(\frac{1}{v}\), i.e. a dependence of the form

\[ \sigma \sim \frac{1}{v} + \mathrm{const}. \tag{43} \]

The presence of a constant term should evidently be ascribed to the effect of potential scattering, which is not taken into account by formula (40). As a rule, the linear dependence between the quantities \(\sigma\) and \(\frac{1}{v}\) (or \(E^{-1/2}\)) extends over the energy region from \(\sim 1\ \mathrm{eV}\) down to hundredths of an eV (thermal neutrons); however, in the absence of low resonance levels it also covers the region of several hundred eV (for example, in Li). In general one should expect that law (42) or (43) should be most clearly expressed in the case of light nuclei. In the case of heavy nuclei, with their closely spaced energy levels, this law is fulfilled only in a narrow energy interval.

Let us also note that in the case of those reactions of splitting and fission of the nucleus which are associated with the neutron’s overcoming a potential barrier, the quantity \(\Gamma_a^{(r)}\), determining the probability of the corresponding process, naturally becomes equal to zero when the neutron energy is insufficient for the occurrence of the given process; the cross section \(\sigma_{\mathrm{tot}}\) for slow neutrons in this case is equal to zero and becomes different from zero only starting with a neutron energy equal to or greater than the excitation threshold of the given reaction.

A dependence of this kind of the quantity \(\sigma_{\mathrm{tot}}\) on the neutron energy occurs, in particular, in the fission of \(Th^{232}\), \(U^{238}\), and \(Np^{237}\). The excitation threshold for the fission of thorium apparently lies near \(1.7\ \mathrm{MeV}\), for \(U^{238}\) about \(0.7\ \mathrm{MeV}^{16}\), and for \(Np^{237}\) about \(0.2\ \mathrm{MeV}^{17}\). The dependence of the fission cross section on neutron energy is presented in Fig. 3. It must be said, however, that in general the dependence of the cross section on energy for neutron reactions (the excitation function of a reaction) has been studied experimentally very little.

As we have seen, resonance effects play an exceptionally important role in the nuclear processes of slow neutrons. With increasing neutron energy, especially for \(E_n > 1\ \mathrm{MeV}\), these effects

become less and less significant, since at high energies the width of the energy levels of a compound nucleus becomes comparable with the distances between the levels and even exceeds these distances, as a result of which the individual levels cease to be distinguishable. Such a smearing of the levels occurs at the lower energy, the heavier the nucleus. Therefore, in passing to the consideration of nuclear reactions of fast neutrons, we shall confine ourselves to the case of heavy nuclei, where the indicated feature of the levels of the compound nucleus is expressed most clearly.

Fig. 3. Fission cross section of neptunium 237 as a function of neutron energy (after Klema).

In this case the dispersion formula for cross sections, naturally, has no meaning, and the theoretical treatment of nuclear processes must proceed from other premises.

Here the statistical method proves especially convenient; it was developed most fully in the work of Weisskopf and Ewing[^18], devoted to the question of the yield of nuclear reactions in the case of particles with energy greater than 1 MeV and nuclei with mass greater than 50. We shall take this work as the basis for the further exposition.

Starting from Bohr’s conception of the two-stage character of the nuclear process (double transition, see above), we shall represent the cross section for the reaction \(Y(n, b)Y'\), where \(Y\) is the initial and \(Y'\) the final nucleus and \(b = n, p, \alpha\) or \(\gamma\), in the form of the following product:

\[ \sigma(n,b)=\pi a^2 \xi_n(E_n)\eta_b(E_n+\varepsilon_n). \tag{44} \]

Here \(\xi_n\) is the probability of energy exchange of the neutron with the nucleus, corresponding to the formation of the compound nucleus \((Y+n)\), and \(\eta_b\) is the relative probability of emission of particle \(b\) by the compound nucleus, whose excitation energy is equal to \(E_n+\varepsilon_n\), if \(\varepsilon_n\) is the binding energy of the neutron in the compound nucleus. The quantity \(\xi_n\) must obviously increase with the neutron energy, approaching 1, since a sufficiently fast neutron, having reached the nucleus, is able to interact with all the particles comprising the latter. According to Weisskopf and Ewing, \(\xi_n \approx 1\) for \(E_n > 1\) MeV.

Let us note here that, since the elastic-scattering cross section of fast neutrons is evidently equal to

\[ \sigma_{\mathrm{el}}=\pi a^2(1-\xi_n), \tag{45} \]

then, in view of $\xi_n \approx 1$, the elastic scattering of fast neutrons by heavy nuclei should constitute only a small part of their total cross section $\sigma$, which is a quantity close to $\pi a^2$ (this reasoning does not take account of potential scattering).

As for the relative probability $\eta_b$, under the assumption that it does not depend on how the compound nucleus was formed, one may put

\[ \eta_b=\Gamma_b:\sum_{b'}\Gamma_{b'}, \tag{46} \]

where $\Gamma_b$ is the mean value of the partial width of the level corresponding to the emission of particle $b$ by the compound nucleus (proportional to the emission probability), and $\sum_{b'}\Gamma_{b'}=\Gamma$ is the total width of the level. According to Weisskopf and Ewing, each of the quantities $\Gamma_b$ may be expressed as

\[ \Gamma_b=f_b(E_n+\varepsilon_n-\varepsilon_b):\omega(E_n+\varepsilon_n), \tag{47} \]

where $f_b$ is a function only of the energy difference $E_n+\varepsilon_n-\varepsilon_b$ ($\varepsilon_b$ is the binding energy of particle $b$ in the compound nucleus), and $\omega$ is the density of levels of the compound nucleus at excitation energy $E_n+\varepsilon_n$. Substitution of (47) into (46) gives

\[ \eta_b=f_b(E_n+\varepsilon_n-\varepsilon_b):\sum_{b'} f_{b'}(E_n+\varepsilon_n-\varepsilon_{b'}). \tag{48} \]

Let us note that the difference $\varepsilon_b-\varepsilon_n$ is equal to the threshold for excitation of the reaction $(n,b)$.

Depending on the character of this reaction, we shall have: $f_n$ in the case of neutron scattering—$(n,n)$, $f_p$ and $f_\alpha$ in the case of disintegration reactions $(n,p)$ and $(n,\alpha)$, $f_\gamma$ in the case of neutron capture by the nucleus—$(n,\gamma)$, and $f_d$ in the case of nuclear fission. As was already indicated above, fission is observed only in a limited number of cases—among the heaviest elements; in the case of the remaining elements $f_d=0$ (if very fast neutrons are not meant). Comparing, further, the functions $f_p$ and $f_\alpha$ with the function $f_n$, we must conclude that they should be comparatively small, especially $f_\alpha$, since the emission of a charged particle by the nucleus is associated with overcoming a potential barrier (Coulomb repulsion), which is especially high in the case of heavy nuclei and $\alpha$-particles; hence follows the small probability of these processes in comparison with the process $(n,n)$. For this reason, and also in view of the experimental fact that, in contrast to $(n,p)$ reactions, the reaction $(n,\alpha)$ is observed only in the case of light nuclei, in what follows we shall take $f_\alpha=0$. Thus, we have

\[ \sum_{b'} f_{b'}=f_\gamma+f_p+f_n \tag{49} \]

and, respectively, for the capture cross sections—\(\sigma_{\mathrm{capt}}\), the disintegration reaction—\(\sigma_p\), and inelastic scattering—\(\sigma_{\mathrm{inel}}\), we obtain:

\[ \sigma_{\mathrm{capt}}=\pi a^2\frac{f_\gamma}{f_\gamma+f_p+f_n}, \tag{50} \]

\[ \sigma_p=\pi a^2\frac{f_p}{f_\gamma+f_p+f_n}, \tag{51} \]

and

\[ \sigma_{\mathrm{inel}}=\pi a^2\frac{f_n}{f_\gamma+f_p+f_n}. \tag{52} \]

Summing these expressions with (45), we obtain for the total cross section

\[ \sigma=\sigma_{\mathrm{el}}+\sigma_{\mathrm{inel}}+\sigma_{\mathrm{capt}}+\sigma_p \]

\[ \sigma=\pi x^2. \tag{53} \]

Consequently, the total cross section in the case of heavy nuclei and fast neutrons, where the resonance effect is absent, must be equal to the geometrical cross section of the nucleus. The cross sections corresponding to the separate processes determining the value of \(\sigma\), as follows from formulas (45), (50), (51), (52), are always smaller than the geometrical cross section.

In the work under consideration, Weisskopf and Ewing calculate the values of the quantities \(f_\gamma\), \(f_p\), and \(f_n\) as functions of the energy of the compound nucleus for Cu \((Z=29)\), Zr \((Z=40)\), and Sn \((Z=50)\). From their calculations it follows that \(f_\gamma\) is several orders of magnitude smaller than \(f_p\), while \(f_p\) is several orders of magnitude smaller than \(f_n\). In view of such a relation among the quantities \(f_\gamma\), \(f_p\), and \(f_n\), the capture cross section and the cross section of the reaction \((n,p)\) must be small in comparison with the cross section for inelastic scattering of fast neutrons, which is in complete agreement with experiment (see below). As for the inelastic-scattering cross section, according to formula (52) it must be of the order of \(\pi x^2\). The inelastically scattered neutrons, according to the calculations of Weisskopf and Ewing, have an energy distribution resembling the Maxwellian distribution, as is seen from Fig. 4, in which curve I represents the distribution of neutrons (by energy) scattered by a Cu nucleus and having an initial energy of 6 MeV, while curve II represents the Maxwell energy distribution.

Let us also add that in the case when the excitation energy remaining in the nucleus as a result of the inelastic scattering of a sufficiently fast neutron exceeds the binding energy of the neutron \(\varepsilon_{n'}\), a second neutron may be emitted by the nucleus [reaction \((n,2n)\)]. For the cross section of this reaction, Weisskopf and Ewing give the following approximate formula:

\[ \sigma(n,2n)=\pi a^2\left[1-\left(1+\frac{\Delta E_n}{\theta}\right)e^{-\frac{\Delta E_n}{\theta}}\right], \tag{54} \]

where

\[ \Delta E_n = E_n - \varepsilon_{n'} \quad \text{and} \quad \Theta = 2\sqrt{\frac{5E_n}{A}}\quad (E_n \text{ in MeV}), \]

obtained under the assumption of a Maxwellian velocity distribution of inelastically scattered neutrons at temperature \(\Theta\).

II. METHOD OF MEASURING CROSS SECTIONS

Measurements of cross sections corresponding to one or another nuclear process caused by neutrons are always reduced to measuring the concentration of neutrons \((n)\) or neutron fluxes \((q)\), which, in the case of capture, disintegration, or fission cross sections, must be supplemented by measurement of the absolute magnitude of the rate of the given process. Measurements of the quantities \(n\) and \(q\) consist in measuring one or another effect produced by neutrons. In this connection, in the case of fast neutrons, most often use is made of the ionizing action of recoil nuclei arising in the elastic collision of a neutron and a nucleus: on its path in a material medium, a recoil nucleus possessing sufficient kinetic energy creates some number of ions, which, in the case of an ionization chamber used as a neutron indicator, are registered in the form of a current or voltage pulse, amplified by means of special radio-engineering amplifiers and transmitted either to an electromechanical pulse counter or to an oscillograph with simultaneous photographic recording.

Fig. 4. Energy distribution of neutrons scattered by a copper nucleus (according to Weisskopf and Ewing).

The number of pulses measured in this way corresponds to the number of recoil nuclei, which in turn is proportional to the number of neutrons entering the ionization chamber during the given interval of time, i.e. to the magnitude of the neutron flux \(q\). In order to obtain recoil nuclei with maximum energy, ionization chambers are usually filled with light gases—hydrogen or helium. In the Wilson chamber, used for registering neutrons, the paths (tracks) of recoil nuclei become visible owing to the formation of droplets on ions serving as condensation centers. Counting the number of tracks here gives the number of recoil nuclei, proportional to the number of neutrons entering the chamber. Thick-layer emulsions are also used for registering neutrons. The tracks of recoil protons arising in them become visible owing to their photographic action and can be counted (under a microscope).

Along with recoil nuclei and their ionizing or photographic action, various nuclear reactions are also often used for the registration of fast neutrons. Measurements of the yield of these reactions give a quantity proportional to the number of incident neutrons. Usually the yield is measured by the magnitude of the electron, positron, or \(\gamma\)-activity caused by the radioactive nuclei produced as a result of the reaction. An example of such a reaction is the reaction \(C^{12}(n,2n)C^{11}\), as a result of which a positron-active isotope of carbon, \(C^{11}\), is produced with a half-life of 20.5 minutes. The threshold of this reaction is 20.4 MeV. Consequently, by means of this reaction neutrons with energy \(E_n > 20.4\) MeV are registered. Another example is the fission of thorium, as a result of which, among other fission fragments, \(\beta\)- and \(\gamma\)-active iodine \(I^{130}\) is formed with a half-life of 12.6 hours. The threshold of this reaction is \(\sim 1.7\) MeV. Often the yield of the fission reaction, used for measuring neutron fluxes, is determined from the number of pulses in an ionization chamber containing the fissionable element, caused by the ionizing action of the fission fragments.

In the case of slow neutrons, recoil nuclei acquire only insignificant energy, insufficient for any appreciable ionization, have a negligible range, and therefore cannot be used to measure neutron concentration. For this reason, exclusively nuclear reactions are used here; their rate, proportional to the number of incident neutrons, as in the case of fast neutrons, is measured by the activity of the radioactive nuclei produced as a result of the reaction.

As is clear from the preceding, with all the methods mentioned for measuring neutron concentration or neutron fluxes, only the relative values of the quantities \(n\) and \(q\) are measured directly. In order to obtain absolute values of these quantities by means of these methods, it is necessary to know the cross sections of those processes that underlie the given method of measurement, i.e. the scattering cross section in the case of using recoil nuclei, or the cross section of that reaction which is used for measuring the number of neutrons. These cross sections must be known for precisely the energy possessed by the neutrons being measured.

Thus, the problem of measuring the numbers \(n\) or \(q\), as well as the problem of measuring the absolute rates of nuclear processes, i.e. the problem of measuring cross sections (with some exceptions; see below), ultimately reduces to the measurement of the absolute value of the number of neutrons. This latter problem is solved in the following way. By using moderators, for which hydrogen-containing substances are employed—most often paraffin or water—the neutrons to be measured are slowed down to very slow (in particular, thermal) neutrons, which are then absorbed by one or another substance entering into reaction with them. The indicator substance is selected

such that the result of this reaction is a radioactive element; in this case measurement of the absolute magnitude of the intensity of the radiation of the latter directly gives the sought number of neutrons, since each slow neutron, as a rule, entering into a reaction of only one type with the given nucleus, gives one radioactive atom. As indicator substances use is made of manganese, which as a result of the reaction \((n,\gamma)\) gives the electron-active isotope \(\mathrm{Mn}^{56}\) with a half-period of 2.59 hours, iodine, which also gives, as a result of \((n,\gamma)\)-reactions, the electron-active isotope \(\mathrm{I}^{128}\) with a half-period of 25 minutes, and other elements. Knowing the number of neutrons incident on the indicator and the absolute magnitude of the activity of the indicator induced by them, it is not difficult to determine the value of the cross section corresponding to the given reaction.

The exception here is the total cross section \(\sigma\), for whose determination it is sufficient to measure relative concentrations or neutron fluxes. In principle, the determination of the quantity \(\sigma\) is carried out in the following way. The substance under investigation is placed between the neutron source and the indicator, which may be some substance reacting to neutrons of the given energy,* or an ionization chamber. If \(q_0\) is the neutron flux, i.e. the number of neutrons emitted every second by the source and reaching the indicator in the absence of the substance under investigation, and \(q\) is the flux recorded by the indicator in the presence of this substance, i.e. the flux attenuated owing to scattering and absorption of neutrons in the substance under investigation, then we shall have

\[ q = q_0 e^{-\sigma C l}, \tag{55} \]

where \(C\) is the number of atoms of the substance under investigation in \(1\ \mathrm{cm}^3\) and \(l\) is the thickness of this substance. Consequently, the sought total cross section \(\sigma\) is found as

\[ \sigma = \frac{1}{Cl}\ln\frac{q_0}{q}, \tag{56} \]

i.e. for its determination it is sufficient to measure the neutron fluxes \(q_0\) and \(q\) in any relative units.

As already stated, to measure the remaining cross sections it is necessary to determine the absolute rate of the corresponding process (together with determination of the magnitude of the neutron flux). In the case of the capture reaction \((n,\gamma)\), the cross section \(\sigma_{\text{cap}}\) is determined by measuring the absolute magnitude of the total activity of the radioactive isotope arising as a result of this process. Taking as the measure of activity the total number of radioactive atoms \(N\) arising, and equating this number to the number of absorbed neutrons, equal to \(q_0\sigma_{\text{cap}}Cl\), from the equality

\[ \sigma_{\text{cap}} = \frac{1}{Cl}\,\frac{N}{q_0} \tag{57} \]

or from the more exact equality

\[ \sigma_{\text{capt}}=-\frac{1}{Cl}\ln\frac{q_0-N}{q_0} \tag{58} \]

one finds the value \(\sigma_{\text{capt}}\). In the case when the number of scattered neutrons can be taken into account and when neutrons of the given energy are capable of exciting only one reaction, the value \(\sigma_{\text{capt}}\) corresponding to this reaction can be determined from formula (56), where \(q\) denotes the neutron flux attenuated by absorption.

In an analogous way the quantities \(\sigma_p\) and \(\sigma_d\) are also determined. The absolute rate of an \((n,p)\) or \((n,\alpha)\) reaction is usually determined from the number of protons or \(\alpha\)-particles registered with the aid of an ionization chamber or a Wilson chamber. This method is, naturally, applicable only in the case of substances that at room temperature are in the gaseous state (in the form of an elemental gas or some volatile compound). The usual method of determining the absolute rate of the fission reaction consists in measuring the number of pulses due to fission fragments and observed in an ionization chamber with electrodes coated with a thin layer of the substance under investigation.

One of the most reliable methods for determining the scattering cross section \(\sigma_{\text{scat}}\) is the method based on measuring the pulses produced by recoil nuclei in an ionization chamber filled with the gas under investigation. This “absolute” method is applicable, however, only in the case of light nuclei and sufficiently fast neutrons, since only in this case do the recoil nuclei acquire sufficient energy. But the absorption of fast neutrons by light nuclei is usually negligibly small. Therefore the total cross section practically coincides with the scattering cross section, the measurement of which is thereby reduced to the measurement of the total cross section \(\sigma\) (see above). For measuring the scattering cross section a relative method is often used, consisting in comparing the desired cross section with that known for some element chosen as a standard. One of the simplest methods of such comparative investigation is the measurement of the flux of neutrons reflected from the substance under investigation and from the standard substance (back scattering).

Up to now, in speaking of the scattering cross section, we have not introduced a distinction between elastic and inelastic scattering. This distinction amounts to the fact that, whereas in elastic scattering the neutron spectrum is practically unchanged (except in cases of scattering by the lightest elements), inelastic scattering is associated with a substantial change of the spectrum, caused by excitation of the scattering nuclei. Therefore, in those cases where inelastic scattering plays an essential role, as occurs for elements heavier than fluorine and for fast neutrons, in order to measure \(\sigma_{\text{el}}\) and \(\sigma_{\text{inel}}\) it is necessary to take account of the changes in the neutron spectrum caused by inelastic scattering. For this purpose two neutron indicators are used—

one possessing a sufficiently high excitation threshold and responding to fast neutrons, and the other registering slow neutrons. To measure the inelastic-scattering cross section, a method is also used that is based on measurements of the activity arising as a result of excitation of nuclei in the inelastic scattering of neutrons.

In the following chapter we give the values of cross sections, measured by various authors, corresponding to various nuclear processes.

III. EXPERIMENTAL DATA

The table given below is based on data from the survey by Dībner, Herrmann, and Grassmann[^19], published in 1942 and covering work through the end of 1940. In our table these data have been supplemented by data published by Folz[^20] in 1943 and relating to cross sections for slow neutrons, as well as by data from individual works published in various journals (mainly in Phys. Rev.) in the subsequent years up to 1947. References to individual works included in the indicated surveys may be found in the latter. We give references chiefly only to those works that were not included in these surveys.

The table is constructed in such a way that, for each element, in order of decreasing energy of the bombarding neutron, there are given the values of the total cross section $\sigma$ (in $10^{-24}\ \mathrm{cm}^2$), the scattering cross section $\sigma_{\mathrm{scatt}}$, and the absorption cross section $\sigma_{\mathrm{abs}}$, representing the cross section for capture, fission reactions, or nuclear fission. In those cases where the nature of the process or the isotope of the given element participating in it is known, this is indicated in the form of a note. In the notes (where this could be established from the literature data) the compound in the form of which the given element was studied is also indicated. The absence of such an indication, as a rule, means that the corresponding measurements were made with the element as such, and not with its compound. In the third column the symbols $d-\mathrm{Li}$, $d-\mathrm{C}$, $d-\mathrm{D}$, etc. denote neutrons obtained by bombarding, respectively, lithium, carbon, deuterium, etc., targets with deuterons. The symbols $\mathrm{Ra}\,\gamma-\mathrm{Be}$ or $\mathrm{ThC'}\,\gamma-\mathrm{D}$, etc. denote photoneutrons arising when beryllium is irradiated by gamma rays of radium, or deuterium by gamma rays of $\mathrm{ThC'}$, etc. Further, $\mathrm{Na}\,\gamma-\mathrm{Be}$, $\mathrm{La}\,\gamma-\mathrm{Be}$, $\mathrm{Na}\,\gamma-\mathrm{D_2O}$, $\mathrm{Mn}\,\gamma-\mathrm{Be}$, $\mathrm{Ga}\,\gamma-\mathrm{D_2O}$, and $\mathrm{Sb}\,\gamma-\mathrm{Be}$ denote photoneutrons produced when the corresponding targets (Be or $\mathrm{D_2O}$) are irradiated by gamma rays from the $\gamma$-active isotopes $\mathrm{Na}^{24}$, $\mathrm{La}^{140}$, $\mathrm{Mn}^{56}$, $\mathrm{Ga}^{72}$, and $\mathrm{Sb}^{124}$. $C$-, $D$-, and $J$-neutrons denote groups of slow neutrons absorbed by cadmium ($C$), rhodium and indium ($D$), and iodine ($J$)[^22]. These neutrons correspond to energies close to the resonance energies of the corresponding elements: namely, for $C$-neutrons—$0.18\ \mathrm{eV}$, for $D$-neutrons—$\sim 1.3$–$1.4\ \mathrm{eV}$, for $J$-neutrons—$\sim 38\ \mathrm{eV}$. The term “slow neutrons” in the table most often means neutrons with energies from several eV to hundredths of an eV. Slow and ther-

mic neutrons (energy equal to \(\frac{1}{40}\) eV or the value \(kT\) at \(T=300^\circ\) abs.) are often synonymous. The latter especially applies to the data presented in Foltz’s compilation. Let us add that \((p-\mathrm{Li})\)-neutrons cited without indicating their energy are apparently neutrons with energy \(\sim 15\) MeV.

Let us now turn to the consideration of individual nuclei that have been most thoroughly studied with respect to their interaction with neutrons.

Hydrogen. In this respect hydrogen has been studied in the greatest detail; its total cross section \(\sigma\) has been measured over a wide interval of neutron energies from 25.4 MeV to 0.01 eV. The data of different authors are here least contradictory, and a large scatter of individual data is observed only for thermal neutrons. The experimental data, with the exception of some old measurements, fit excellently on the theoretical curve obtained by Bohm and Richman\({}^{83}\) on the basis of certain assumptions about the form of the potential function characterizing the interaction of the neutron and proton. This curve is shown in Fig. 5, where, along with data obtained by means of strictly monochromatic neutrons, the results of measurements with photoneutrons are also presented (crosses at \(E_n < 1\) MeV). Apparently, the insufficient monochromaticity of the RaTh\(\gamma\) and Rn\(\gamma\) photoneutrons is the reason for the departure of the corresponding points from the curve.

Fig. 5. Dependence of the hydrogen scattering cross section on neutron energy (the theoretical curve calculated by Bohm and Richman; points—experimental values obtained by various authors).

From the theoretical curve for thermal neutrons one obtains \(\sigma=21.0\). Let us note that the cross-section values for hydrogen as functions of neutron energy should be regarded as having been measured so accurately that they can be used as standards for determining unknown cross sections, as is done by some authors.

Because of the absence of resonance levels in the compound nucleus \(n+p(d)\), and also because of the smallness of the capture cross section, the total cross section of hydrogen at all neutron energies is practically equal to the elastic-scattering cross section (see the table). As for the capture cross section, corresponding to the reaction \(n^1+p^1=d^2+\gamma\), individual

the values of this quantity measured by various authors agree rather well with one another, and also with the theoretical value calculated by Rarita and Schwinger[^36]. Let us add that, according to the theory, \(\sigma_{\mathrm{capt}}\) of hydrogen varies with neutron energy proportionally to \(E_n^{-1/2}\), i.e., inversely proportional to the neutron velocity.

Deuterium. The action cross section, like the cross section of hydrogen, increases smoothly as the neutron energy decreases. Here \(\sigma\) at all energies is also practically equal to \(\sigma_{\mathrm{scatt}}\); \(\sigma_{\mathrm{absor}}\) is relatively still smaller than \(\sigma_{\mathrm{absor}}\) of hydrogen.

Helium. In contrast to hydrogen and deuterium, the total cross section of helium has a sharp resonance maximum at an energy \(\sim 1\ \mathrm{MeV}\), revealed both in the behavior of the quantity \(\sigma\) with the energy \(E_n\), and in the behavior of the quantity \(\sigma_{\mathrm{el.\,scatt}}(\mathrm{He}) : \sigma_{\mathrm{el.\,scatt}}(\mathrm{H})\). This maximum is evidently caused by the resonance level of the compound nucleus \(\mathrm{He}^5\), which is also observed in the reaction \(d^2 + \mathrm{Li}^7 = \mathrm{He}^4 + \mathrm{He}^5\). In the latter case, from measurements of the range of \(\alpha\)-particles it follows that the nucleus \(\mathrm{He}^5\) is in an excited state with excitation energy equal to \(0.84\ \mathrm{MeV}\)[^41].

Lithium. The total cross section of lithium, up to \(E_n\) of the order of several hundred eV, almost does not vary with neutron energy. At \(E_n < 250\ \mathrm{eV}\), \(\sigma\) increases with decreasing energy according to a linear law (relative to \(E_n^{-1/2}\)) and in the region of thermal neutrons reaches a value 20–30 times greater than its value at large \(E_n\). This increase in \(\sigma\) is caused by the growth of \(\sigma_{\mathrm{absor}}\), corresponding to the reaction \(n^1 + \mathrm{Li}^6 = \mathrm{He}^4 + \mathrm{H}^3\), since for slow neutrons the quantity \(\sigma\) proves to be practically equal to \(\sigma_{\mathrm{absor}}\). In the calculation per lithium isotope (\(\mathrm{Li}^6\)) participating in the reaction, \(\sigma_{\mathrm{absor}}\) is expressed by a number \(\sim 900\).

Beryllium. In the case of beryllium, \(\sigma \simeq \sigma_{\mathrm{scatt}}\) slowly increases as the neutron energy decreases, increasing by a factor of 2–3 when \(E_n\) decreases from \(0.83\ \mathrm{MeV}\) to \(\sim 0.01\ \mathrm{eV}\). \(\sigma_{\mathrm{absor}}\) is relatively small, amounting to \(\sim 0.1\%\) of \(\sigma\) (for thermal neutrons).

Boron. The total cross section of boron, practically equal for fast neutrons to the scattering cross section, increases as \(E_n\) decreases. At \(E_n < 1000\ \mathrm{eV}\), the growth of the quantity \(\sigma\), which more and more approaches \(\sigma_{\mathrm{absor}}\), corresponding to the reaction \(\mathrm{B}^{10} + n^1 = \mathrm{Li}^7 + \mathrm{He}^4\), follows a linear dependence on \(E_n^{-1/2}\). For slow neutrons \(\sigma\) is practically equal to \(\sigma_{\mathrm{absor}}\), since \(\sigma_{\mathrm{scatt}}\) here amounts to less than \(1\%\) of \(\sigma\). In the calculation per isotope \(\mathrm{B}^{10}\), \(\sigma_{\mathrm{absor}}\) is expressed by a number of the order of 3000.

Carbon. In view of the smallness of \(\sigma_{\mathrm{absor}}\), amounting to about \(0.1\%\) of \(\sigma\), the latter quantity over the entire broad energy interval studied (from \(25.4\ \mathrm{MeV}\) to \(0.025\ \mathrm{eV}\)) is practically equal to \(\sigma_{\mathrm{scatt}}\). When the neutron energy is decreased from \(25.4\ \mathrm{MeV}\) to \(0.25\ \mathrm{eV}\), \(\sigma\) increases by \(\sim 5\) times. The smooth behavior of \(\sigma\) with \(E_n\) is disturbed by the presence of two weak maxima at energy values of about \(4.3\) and \(3.7\ \mathrm{MeV}\), indicating the presence of two resonance levels in the nucleus \(\mathrm{C}^{13}\). Almost twice smal-

An even larger cross section for elastic scattering at an angle of \(100^\circ\), compared with scattering at an angle of \(45^\circ\), indicates an asymmetry of elastic scattering. This is also indicated by the comparatively small value of the cross section for backward scattering, i.e. scattering at \(180^\circ\).

Nitrogen. In the case of nitrogen, the total cross section for fast neutrons, practically equal to the scattering cross section, changes very little in the region of high energies. The absorption cross section, corresponding to the reaction \(n^1 + N^{14} = C^{14} + p^1\) and having two resonance maxima near \(E_n = 1.45\) and \(0.70\ \mathrm{MeV}\), amounts at the maxima to \(\sim 5\%\) and \(10\%\) of the value of \(\sigma\). Near \(E_n = 1.45\ \mathrm{MeV}\) a maximum of \(\sigma_{\text{abs}}\), corresponding to the reaction \(n^1 + N^{14} = B^{11} + He^4\), is also observed. On passing into the region of slow neutrons both \(\sigma\) and \(\sigma_{\text{abs}}\) exhibit a rapid rise, with \(\sigma\) increasing severalfold, and \(\sigma_{\text{abs}}\) (reaction \(n^1 + N^{14} = C^{14} + p^1\)) by several hundred times. The latter quantity in the region of small energies apparently follows the proportionality law

\[ E_n^{-1/2}. \]

Oxygen. The total cross section of oxygen, apparently equal to the scattering cross section throughout the entire energy interval studied (from \(\sim 15\ \mathrm{MeV}\) to \(0.025\ \mathrm{eV}\)), varies irregularly with energy, revealing a series of (resonance?) maxima (at \(4.0\ \mathrm{MeV}\) and below); \(\sigma\) for thermal neutrons has the same order of magnitude as for fast ones. \(\sigma_{\text{abs}}\) is very small.

Fluorine. The total cross section of fluorine, throughout the entire energy interval studied (from \(\sim 15\ \mathrm{MeV}\) to \(0.025\ \mathrm{eV}\)), equal to the scattering cross section, increases as the neutron energy decreases, reaches a low maximum near \(0.2\ \mathrm{MeV}\), and then falls. The value of \(\sigma\) for slow neutrons is \(2\text{–}3\) times smaller than the maximum value. \(\sigma_{\text{abs}}\) does not exceed \(2\%\) of \(\sigma\).

Sodium. \(\sigma\), practically equal to \(\sigma_{\text{scat}}\), as \(E_n\) decreases from \(\sim 3\ \mathrm{MeV}\), exhibits an irregular dependence on \(E_n\), apparently due to the presence of several resonance maxima. \(\sigma\) for thermal neutrons exceeds the value at \(E_n \approx 15\ \mathrm{MeV}\) by only \(\sim 2\) times. The absorption cross section for slow neutrons is about \(10\%\) of the value of \(\sigma\). The number \(\sigma_{\mathrm{T}} = 16\) given in the table is apparently associated with a gross error.

Magnesium. The variation of \(\sigma\) with neutron energy in the case of magnesium is similar to that observed for sodium. Here \(\sigma\) is also practically equal to \(\sigma_{\text{scat}}\); \(\sigma_{\text{abs}}\) for slow neutrons does not exceed \(10\%\) of \(\sigma\).

Aluminium. Al also has a variation analogous to that of \(\sigma\) in the case of Na and Mg. According to the latest data\(^{72}\), in the energy interval from \(1\ \mathrm{MeV}\) to \(0.01\ \mathrm{MeV}\) there are at least 10 low resonance maxima. Here \(\sigma\) is also practically equal to \(\sigma_{\text{scat}}\), and \(\sigma_{\text{abs}}\) for slow neutrons amounts to about \(10\%\) of \(\sigma\). An asymmetry of elastic scattering is found from the sharp dependence of the cross section on the scattering angle.

Silicon. The behavior of $\sigma$ for Si is similar to the behavior of $\sigma$ for Na, Mg, and Al. $\sigma$, apparently, is equal to $\sigma_{\mathrm{scat}}$. For slow neutrons $\sigma_{\mathrm{abs}}$ is of the order of $\sim 1\%$ of $\sigma$.

Phosphorus. In the case of phosphorus, $\sigma$ changes little with the energy of fast neutrons. On going over to slow neutrons it increases by a factor of 3–4. $\sigma$ is practically equal to $\sigma_{\mathrm{scat}}$; $\sigma_{\mathrm{abs}}$ for slow neutrons amounts to several percent of $\sigma$.

Sulfur. $\sigma$ changes little with $E_n$ over the whole range from fast $(d-\mathrm{Li})$ neutrons to slow ones. $\sigma$, apparently, is close to $\sigma_{\mathrm{scat}}$; $\sigma_{\mathrm{abs}}$ for slow neutrons amounts to about 20% of $\sigma$.

Chlorine. $\sigma$, slowly increasing with decreasing neutron energy, increases in order of magnitude by $\sim 10$ times on going over to slow neutrons. $\sigma \simeq \sigma_{\mathrm{scat}}$ for fast neutrons and becomes greater than $\sigma_{\mathrm{scat}}$ in the case of slow neutrons, for which $\sigma_{\mathrm{abs}}$ is of the order of $\sigma$.

Potassium. $\sigma$ shows an irregular behavior with $E_n$. $\sigma_{\mathrm{abs}}$ for slow neutrons apparently has the order of magnitude of $\sigma_{\mathrm{scat}}$.

Calcium. $\sigma$ changes little with neutron energy and only on going over to slow neutrons increases by a factor of 2–3. $\sigma$ is practically equal to $\sigma_{\mathrm{scat}}$. For slow neutrons $\sigma_{\mathrm{abs}}$ amounts to 3–5% of $\sigma$.

Titanium. $\sigma$, changing little with neutron energy, increases several times on going over to slow neutrons, for which $\sigma_{\mathrm{abs}}$ is close to $\sigma_{\mathrm{scat}}$.

Chromium. $\sigma$ changes little with neutron energy and, on going from fast $(d-\mathrm{Li})$ neutrons to slow ones, increases by less than a factor of two. For fast neutrons $\sigma \simeq \sigma_{\mathrm{scat}}$, while for slow neutrons $\sigma_{\mathrm{abs}}$ is comparable with $\sigma_{\mathrm{scat}}$.

Manganese. For fast neutrons $\sigma \simeq \sigma_{\mathrm{scat}}$ changes little with the value of $E_n$. Near 300 eV a sharp maximum of resonance scattering is observed. For $E_n < 30\,\mathrm{eV}$, $\sigma$ varies with $E_n^{-1/2}$ according to a linear law. For thermal neutrons $\sigma$ is close to $\sigma_{\mathrm{abs}}$.

Iron. For fast neutrons $\sigma \simeq \sigma_{\mathrm{scat}}$ almost does not change with $E_n$. On going over to slow neutrons $\sigma$ increases several times. For slow neutrons $\sigma_{\mathrm{abs}}$ amounts to 20–30% of the value of $\sigma$. From the sharp dependence of $\sigma_{\mathrm{scat}}$ on the scattering angle there follows an asymmetry of elastic scattering. Comparison of $\sigma_{\mathrm{scat}}$ and $\sigma_{\mathrm{el}}$ at identical scattering angles indicates the predominance of inelastic scattering of fast neutrons $(d-\mathrm{D})$ over elastic scattering.

Cobalt. For fast neutrons $\sigma \simeq \sigma_{\mathrm{scat}}$, changing comparatively little with neutron energy, at $E_n = 115\,\mathrm{eV}$ reveals a sharp resonance maximum. For $E_n < 5\,\mathrm{eV}$, $\sigma$ depends linearly on $E_n^{-1/2}$. $\sigma_{\mathrm{abs}} \simeq \sigma_{\mathrm{scat}}$ at $E_n = 1\,\mathrm{eV}$. For slow neutrons $\sigma_{\mathrm{abs}}$ is $\sim 5$ times larger than $\sigma_{\mathrm{scat}}$.

Nickel. \(\sigma\) increases as the neutron energy decreases (from \(\sim 3\) MeV). For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}} \simeq 30\%\,\sigma\).

Copper. The course of \(\sigma\) with neutron energy is the same as in the case of Ni. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}} \simeq 30\%\,\sigma\). \(\sigma_{\mathrm{abs}}\), apparently, is proportional to \(E_n^{-1/2}\). From the dependence of \(\sigma_{\mathrm{scatt}}\) on angle follows an asymmetry of the elastic scattering of fast neutrons. \(\sigma_{\mathrm{inel}}\) is of the order of magnitude of \(\sigma_{\mathrm{el}}\).

Zinc. \(\sigma\) increases with decreasing \(E_n\), passing through a maximum at small \(E_n\). For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}}\) amounts to \(\sim 20\%\) of \(\sigma\). Asymmetry of the elastic scattering.

Arsenic. As the neutron energy decreases (from fast to thermal), \(\sigma\) increases by \(\sim 2\) times. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}}\) is comparable with \(\sigma_{\mathrm{scatt}}\). \(\sigma_{\mathrm{abs}}\), apparently, is proportional to \(E_n^{-1/2}\).

Selenium. On passing from fast neutrons to slow ones, \(\sigma\) increases by \(\sim 5\) times. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}}\) is close to \(\sigma_{\mathrm{scatt}}\).

Bromine. \(\sigma\) increases with decreasing \(E_n\). In the region of slow neutrons there is a sharp resonance (?). For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma_{\mathrm{abs}}\) is comparable with \(\sigma_{\mathrm{scatt}}\).

Strontium. \(\sigma \simeq \sigma_{\mathrm{scatt}}\) and changes little with neutron energy, increasing by \(\sim 2\) times in the transition from fast neutrons to slow ones. For the latter \(\sigma_{\mathrm{abs}} \simeq 15\%\,\sigma\).

Zirconium. \(\sigma\) has three resonance maxima: at \(E_n = 7.6\), 2.3 and 1.09 eV. For \(E_n < 0.6\) eV, \(\sigma\) depends linearly on \(E_n^{-1/2}\).

Niobium. For \(E_n < 1\) eV, \(\sigma\) depends linearly on \(E_n^{-1/2}\).

Molybdenum. \(\sigma\) changes little with \(E_n\). For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\). \(\sigma_{\mathrm{abs}}\) for slow neutrons is of the order of magnitude of \(\sigma_{\mathrm{scatt}}\).

Rhenium. In the region of slow neutrons \(\sigma_{\mathrm{abs}}\) exhibits a sharp resonance maximum. \(\sigma_{\mathrm{abs}}\) is close to \(\sigma\).

Silver. \(\sigma\) increases with decreasing \(E_n\), passing through several resonance maxima. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\). For \(E_n < 0.5\) eV, \(\sigma\) depends linearly on \(E_n^{-1/2}\). For slow neutrons \(\sigma_{\mathrm{abs}}\) is comparable with \(\sigma\) and exceeds \(\sigma_{\mathrm{scatt}}\) by a whole order of magnitude.

Cadmium. \(\sigma\) increases with decreasing \(E_n\), passing through a resonance maximum near \(E_n = 0.18\) eV. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{scatt}}\), for slow ones \(\sigma \simeq \sigma_{\mathrm{abs}}\).

Indium. In the region of slow neutrons \(\sigma\) exhibits several resonance maxima, the largest of which is the maximum near \(E_n = 1.44\) eV. \(\sigma \simeq \sigma_{\mathrm{abs}}\).

Tin. In the interval \(E_n\) from \(\sim 15\,\mathrm{eV}\) to \(E_n<1\,\mathrm{eV}\), \(\sigma \simeq \sigma_{\mathrm{sc}}\) changes by a factor of \(\sim 1.5\). For slow neutrons \(\sigma_{\mathrm{abs}} \simeq 10\%\,\sigma\). An asymmetry of scattering is observed.

Antimony. \(\sigma\) increases as \(E_n\) decreases, passing through several resonance maxima and, for \(E_n<1\,\mathrm{eV}\), following a linear dependence on \(E_n^{-1/2}\). For fast neutrons \(\sigma \simeq \sigma_{\mathrm{sc}}\); for slow neutrons, \(\sigma_{\mathrm{abs}}\) is close to \(\sigma_{\mathrm{sc}}\).

Tellurium. For slow neutrons \(\sigma_{\mathrm{abs}}\) is of the order of \(\sigma_{\mathrm{sc}}\) and, apparently, proportional to \(E_n^{-1/2}\).

Iodine. The \(\sigma\) of iodine increases weakly as the neutron energy decreases (approximately by a factor of two in going from fast neutrons to thermal ones). In the region around 38 and 20 eV there are at least two resonance maxima. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{sc}}\); for slow neutrons \(\sigma_{\mathrm{abs}}\) is \(\sim 2/3\) of \(\sigma\). For \(E_n<15\,\mathrm{eV}\), \(\sigma\) depends linearly on \(E_n^{-1/2}\).

Barium. \(\sigma \simeq \sigma_{\mathrm{sc}}\) and changes little with neutron energy. For slow neutrons \(\sigma_{\mathrm{abs}} \simeq 10\%\,\sigma\) and, apparently, is proportional to \(E_n^{-1/2}\).

Europium and gadolinium. Resonance absorption in the region of slow neutrons.

Dysprosium. Resonance absorption in the region of slow neutrons. For slow and thermal neutrons \(\sigma_{\mathrm{abs}} \simeq \sigma\).

Tantalum. In the region of slow neutrons \(\sigma\) passes through a number of resonance maxima. For \(E_n<1\,\mathrm{eV}\), \(\sigma\) depends linearly on \(E_n^{-1/2}\). For slow neutrons \(\sigma_{\mathrm{abs}} \simeq \dfrac{3}{4}\sigma\). Different, strongly differing values of the capture cross section \((20.6\ \text{and}\ 0.034)\) correspond to different degrees of excitation of the nucleus \( \mathrm{Ta}^{182}\).

Tungsten. \(\sigma\) increases as the neutron energy decreases, passing through a number of resonance maxima. For fast neutrons \(\sigma \simeq \sigma_{\mathrm{sc}}\); for slow neutrons \(\sigma\) is close to \(\sigma_{\mathrm{abs}}\). For \(E_n<1\,\mathrm{eV}\), \(\sigma\) depends linearly on \(E_n^{-1/2}\).

Osmium. In the region of small \(E_n\), there are a number of resonance maxima of \(\sigma\). For \(E_n<4\,\mathrm{eV}\), \(\sigma\) depends linearly on \(E_n^{-1/2}\). For thermal neutrons \(\sigma_{\mathrm{abs}}\) is close to \(\sigma_{\mathrm{sc}}\).

Iridium. In the region of slow neutrons, there are a number of resonance maxima of \(\sigma\). \(\sigma\) depends linearly on \(E_n^{-1/2}\).

Platinum. A number of resonance maxima of \(\sigma\) occur at \(E_n=1000\,\mathrm{eV}\) and below. For \(E_n<0.8\,\mathrm{eV}\), \(\sigma\) depends linearly on \(E_n^{-1/2}\). \(\sigma_{\mathrm{abs}}\) is of the order of \(\sigma_{\mathrm{sc}}\).

Gold. \(\sigma\) has a high maximum at \(E_n = 4.8 \text{ eV}\). For slow neutrons \(\sigma_{\text{abs}}\) is close to \(\sigma\) and, apparently, is proportional to \(E_n^{-1/2}\).

Mercury. In the region of fast neutrons \(\sigma \simeq \sigma_{\text{scat}}\) and changes little with the value of \(E_n\). For slow neutrons \(\sigma\) depends linearly on \(E_n^{-1/2}\), \(\sigma_{\text{abs}}\) is proportional to \(E_n^{-1/2}\) and is practically equal to \(\sigma\).

Thallium. \(\sigma_{\text{scat}}\) changes little with neutron energy (from \(0.86\ \text{MeV}\) to \(0.025\ \text{eV}\)). Near \(E_n = 1100\) and \(270\ \text{eV}\) \(\sigma\) has a maximum and, for \(E_n < 10\ \text{eV}\), depends linearly on \(E_n^{-1/2}\). \(\sigma_{\text{abs}}\) for thermal neutrons amounts to about \(30\%\) of \(\sigma\).

Lead. \(\sigma \simeq \sigma_{\text{scat}}\) increases with decreasing neutron energy, increasing by a factor of \(2\)—\(2.5\) in going from \((d-\mathrm{Li})\)-neutrons to slow ones. \(\sigma_{\text{abs}}\) is relatively small. The inelastic-scattering cross section constitutes a considerable fraction of \(\sigma_{\text{scat}}\). The scattering is asymmetric.

Bismuth. \(\sigma \simeq \sigma_{\text{scat}}\) increases with decreasing neutron energy (by about a factor of \(2\)). \(\sigma_{\text{abs}}\) is relatively small. The scattering is asymmetric.

A consideration of the experimental data relating to individual elements—data not always unambiguous and reliable and, with few exceptions, insufficiently complete—nevertheless makes it possible to draw certain general conclusions. These conclusions may be formulated in the form of the following propositions.

The total cross section, as a rule, increases with decreasing neutron energy. An especially rapid increase in the value of \(\sigma\) is observed in the region of slow neutrons, which is mainly due to the linear dependence of \(\sigma\) on \(1/v \sim E_n^{-1/2}\). This dependence has been established experimentally for Li, B, Mn, Co, Zr, Nb, Sb, I, Ta, W, Os, Ir, Pt, Hg, and Tl; it is also manifested more or less distinctly, apparently, in the cases of N, Cu, As, Te, and Ba. The smooth course of the value of \(\sigma\) with \(E_n\) is disturbed by resonance maxima, which are more often connected with resonance absorption of neutrons, more rarely with resonance scattering. In the region of fast neutrons the total cross section is practically always equal to the scattering cross section. A sharply expressed asymmetry of scattering is observed, manifested in a sharp dependence of \(\sigma_{\text{scat}}\) on the scattering angle. For heavier nuclei, inelastic scattering constitutes a considerable fraction of the total scattering. The absorption cross section, constituting a small part of the total cross section for fast neutrons, in the case of slow (in particular, thermal) neutrons, as a rule, becomes a noticeable quantity. However, at present it is difficult to establish any definite dependence between the value of \(\sigma_{\text{abs}}\) and the nuclear charge (or any other of its characteristics). Thus, nuclei D, Be, C, O, and Si have relatively very small absorption cross sections \((<1\%\) of \(\sigma)\). \(\sigma_{\text{abs}}\) of the order of \(1\)—\(2\%\) of \(\sigma\) have—

south: H, F, and Br. Significant absorption cross sections, amounting to 10–30% of \(\sigma\), are observed for N, Na, Mg, Al, P(?), S, Ca, Fe, Zn, Ga, Sr, Nb, Sn, Ba, Tl, Pb, Bi(?) and U. Finally, Li, B, Cl, K, Ti, V, Cr, Mn, Co, Ni, Cu(?), As, Se, Mo(?), Rh, Ag, Cd, In,

Fig. 6. Dependence of the nuclear radius, calculated from the formula \(a=\sqrt{\frac{\sigma}{\pi}}\) \((\sigma\)—total cross section for fast neutrons), on atomic weight \(A\).

Sb, Te, I, La, Nd, Sm, Eu, Gd, Dy, Ta, W, Re, Au, Hg and Th(?) have \(\sigma_{\mathrm{abs}}\) exceeding 30% of \(\sigma\).

In conclusion, let us dwell further on the nature of the variation of the total cross section for fast neutrons in the periodic system of the elements. According to the theory (see above), for sufficiently heavy nuclei and fast neutrons satisfying the condition \(\frac{\lambda}{2\pi} \ll a\), the total cross section should be equal to the geometrical cross section of the nucleus, i.e. \(\sigma=\pi a^2\) (53). From the formula

\[ \lambda = \frac{h}{\sqrt{2mE_n}} \tag{59} \]

we obtain the following relation between the magnitude \(\frac{\lambda}{2\pi}\) and the neutron energy \(E_n\) (in MeV):

\[ \frac{\lambda}{2\pi}=\frac{0.45\cdot 10^{-12}}{\sqrt{E_n}} \ \mathrm{cm}, \]

from which it follows that, for \(E_n > 1 \mathrm{MeV}\),

\[ \frac{\lambda}{2\pi} < 0.45 \cdot 10^{-12}\ \mathrm{cm}. \]

Thus, since, on the other hand, the radii of the nuclei of sufficiently heavy elements are of the order of \(10^{-12}\ \mathrm{cm}\), for \((d-\mathrm{Li})\)-neutrons with energy \(\sim 15 \mathrm{MeV}\) we may regard the condition

\[ \frac{\lambda}{2\pi} \ll a \]

as satisfied. In Fig. 6 are plotted the values of nuclear radii (including also light nuclei), calculated by formula (53) from \(\sigma\) for \((d-\mathrm{Li})\)-neutrons (circles) as a function of \(\sqrt[3]{A}\) (\(A\) is the atomic weight). Crosses denote the values of the quantity \(a\), calculated by the same formula, but from \(\sigma\) for \((d-\mathrm{D})\)-neutrons (\(E_n = 3 \div 2 \mathrm{MeV}\)). From Fig. 6 it is seen that, despite the considerable scatter of the individual values of the quantity

\[ \sqrt{\frac{\sigma}{\pi}}, \]

the general tendency in the change of this quantity with neutron energy is expressed approximately by a linear dependence on \(\sqrt[3]{A}\). The straight line in Fig. 6 corresponds to the formula

\[ a = \sqrt{\frac{\sigma}{\pi}} = \left(0.4 + 0.15\sqrt[3]{A}\right) 10^{-12}\ \mathrm{cm}. \tag{60} \]

This formula can be interpreted in the following way. Denoting the density of the nucleus by \(\rho\), we have

\[ \frac{4\pi}{3} a^3 \rho = \frac{A}{N}, \]

where \(N\) is Avogadro’s number, whence it follows that

\[ a \sim \sqrt[3]{A}, \]

on the assumption that the density of different nuclei is approximately the same. The linear dependence of the quantity

\[ a = \sqrt{\frac{\sigma}{\pi}} \]

on \(\sqrt[3]{A}\), expressed by the approximate formula (60), may serve as confirmation of the correctness of this assumption. As for the constant term in formula (60), it is evidently due to the dimensions of the neutron itself and to the finite range of the nuclear forces, as a result of which the “screening” radius of the nucleus for neutrons proves to be greater than the geometrical radius by a certain constant quantity of the order of \(10^{-12}\ \mathrm{cm}^{114}\). The fact that some points deviate considerably from the straight line in Fig. 6 requires special investigation.

In general it must be said that the study of the cross sections of nuclear reactions as functions of neutron energy is still in an embryonic state. Only as a result of systematic investigations in this field will it be possible to give a correct interpretation of all the regularities observed here, which must play an exceptionally important role in the creation of a general dynamics of the atomic nucleus.

Table

Cross sections of neutron nuclear reactions (in \(10^{-24}\ \mathrm{cm}^2\))

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
1 H	25,4	\(d\)—Li	\(0,39 \pm 0,03\)			\(^{24}\) Paraffin
1 H	21,1	″	\(0,41 \pm 0,09\)			\(^{25}\) ″
1 H	19,6	″	\(0,52 \pm 0,09\)			\(^{25}\) ″
1 H	18,1	″	\(0,55 \pm 0,08\)			\(^{25}\) ″
1 H	16,5	″	\(0,66 \pm 0,10\)			\(^{25}\) ″
1 H	\(\sim 15\)	″	0,6			\(^{19}\) ″
1 H	14,8	″	\(0,61 \pm 0,09\)			\(^{25}\) Paraffin
1 H	13,5	″		\(0,94 \pm 0,019\)		\(^{26}\)
1 H	12,8	″	\(0,83 \pm 0,09\)			\(^{45}\) Paraffin
1 H	12,5	\(d\)—\(^3\)		\(0,69 \pm 0,11\)		\(^{26}\)
1 H	10,6	\(d\)—Li	\(0,78 \pm 0,09\)			\(^{25}\) Paraffin
1 H	9,3	\(d\)—Be	\(0,92 \pm 0,08\)			\(^{25}\) ″
1 H	6,5	″	\(1,40 \pm 0,11\)			\(^{25}\) ″
1 H	6,0	\(d\)—D		\(1,32 \pm 0,12\)		\(^{27}\) Cyclohexane
1 H	5,5	″		\(1,48 \pm 0,06\)		\(^{27}\) ″
1 H	5,0	″		\(1,63 \pm 0,05\)		\(^{27}\) ″
1 H	4,5	″		\(1,83 \pm 0,10\)		\(^{27}\) ″
1 H	4,1	\(d\)—Be		\(1,73 \pm 0,05\)		\(^{28}\)
1 H	4,0	\(d\)—D		\(1,85 \pm 0,09\)		\(^{27}\) Cyclohexane
1 H	3,5	″		\(2,09 \pm 0,09\)		\(^{27}\)
1 H	3,0	″		\(2,33 \pm 0,13\)		\(^{27}\) ″
1 H	2,8–2,1	″	\(2,41 \ldots 2,74 \pm 1,0\)			\(^{28}\)
1 H	—	″		1–1,3		\(^{19}\)
1 H	2,6	″		\(2,60 \pm 0,05\)		\(^{27}\) Cyclohexane
1 H	2,0	″		\(2,96 \pm 0,07\)		\(^{27}\) ″
1 H	1,6	\(d\)—C		\(3,36 \pm 0,08\)		\(^{27}\) ″
1 H	\(1,0 \pm 0,1\)	″		\(4,16 \pm 0,15\)		\(^{27}\) ″

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
\(^{1}\mathrm{H}\)	0.97	\(p\)—Li		\(4.45 \pm 0.08\)		\(^{27}\) Cyclohexane
\(^{1}\mathrm{H}\)	0.90	RaTh \(\gamma\)—Be	\(3.70 \pm 0.35\)			\(^{29}\)
\(^{1}\mathrm{H}\)	0.90	”	\(5.5 \pm 1.1\)			\(^{30}\)
\(^{1}\mathrm{H}\)	0.86	”	\(2.8 \pm 0.8\)			\(^{31}\) \(\mathrm{H_2O}\)
\(^{1}\mathrm{H}\)	—	Fission of U	5.2			\(^{19}\)
\(^{1}\mathrm{H}\)	0.72	\(p\)—Li		\(5.22 \pm 0.12\)		\(^{27}\) Cyclohexane
\(^{1}\mathrm{H}\)	0.490	”	\(6.33 \pm 0.21\)			\(^{32}\) Polyethylene
\(^{1}\mathrm{H}\)	0.46	”		\(6.52 \pm 0.15\)		\(^{27}\) Cyclohexane
\(^{1}\mathrm{H}\)	0.35	”		\(7.15 \pm 0.24\)		\(^{27}\) ”
\(^{1}\mathrm{H}\)	0.265	”	\(9.12 \pm 0.24\)			\(^{32}\) Polyethylene
\(^{1}\mathrm{H}\)	0.210	RaTh \(\gamma\)—D	\(5.0 \pm 1.0\)			\(^{31}\) \(\mathrm{H_2O}\)
\(^{1}\mathrm{H}\)	0.133 and 0.530	Rn \(\gamma\)—Be		\(8.6 \pm 2.3\)		\(^{33}\)
\(^{1}\mathrm{H}\)	0.095	\(p\)—Li	\(13.46 \pm 0.39\)			\(^{32}\) Polyethylene
\(^{1}\mathrm{H}\)	0.035	”	\(16.74 \pm 0.41\)			\(^{32}\) ”
\(^{1}\mathrm{H}\)	Slow	—	35			\(^{19}\)
\(^{1}\mathrm{H}\)	Thermal	—	24.0			\(^{19}\)
\(^{1}\mathrm{H}\)	”	—	\(22.0 \pm 4\)			\(^{19}\) \(o\mathrm{H}_2, p\mathrm{H}_2, 300^\circ\); [[unclear: abbreviation]]
\(^{1}\mathrm{H}\)	”	—	56			\(^{19}\) \(o\mathrm{H}_2, 300^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	29			\(^{19}\) \(p\mathrm{H}_2, 300^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	\(39 \pm 5\)			\(^{19}\) \(o\mathrm{H}_2, 130^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	\(10 \pm 4\)			\(^{19}\) \(p\mathrm{H}_2, 130^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	\(39 \pm 5\)			\(^{19}\) \(o\mathrm{H}_2, 100^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	\(19 \pm 4\)			\(^{19}\) \(p\mathrm{H}_2, 130^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	79			\(^{19}\) \(o\mathrm{H}_2, \sim120^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—	18			\(^{19}\) \(p\mathrm{H}_2, \sim120^\circ\) abs.
\(^{1}\mathrm{H}\)	”	—			\(0.27 \pm 0.02\)	\(^{19}\) \(n^1 + \mathrm{H}^1 = \mathrm{D}^2 + \gamma\)
\(^{1}\mathrm{H}\)	”	—			\(0.22{-}0.31\)	\(^{20}\) \(n^1 + \mathrm{H}^1 = \mathrm{D}^2 + \gamma\)
\(^{1}\mathrm{H}\)	”	—			0.25	\(^{20}\) \(n^1 + \mathrm{H}^1 = \mathrm{D}^2 + \gamma\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
\(^{1}\mathrm H\)	Therm.	—			0,307	\(^{34}\ n^{1}+\mathrm H^{1}=\mathrm D^{2}+\gamma\)
\(^{1}\mathrm H\)	"	—			0,33	\(^{35}\ n^{1}+\mathrm H^{1}=\mathrm D^{2}+\gamma\)
\(^{1}\mathrm H\)	"	—			0,302	\(^{27}\ n^{1}+\mathrm H^{1}=\mathrm D^{2}+\gamma\) theoretical ?
\(^{1}\mathrm D\)	—	\(d-\mathrm{Li}\)	\(1,68\pm0,07\)			\(^{37}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	14	"			\(0,04—0,09\)	\(^{26}\ n^{1}+\mathrm D^{2}=p^{1}+2n^{1}\)
\(^{1}\mathrm D\)	13,5	"		\(0,864\pm0,028\)		\(^{26}\)
\(^{1}\mathrm D\)	12,5	\(d-\mathrm B\)		\(0,78\pm0,12\)		\(^{26}\)
\(^{1}\mathrm D\)	6,0	\(d-\mathrm D\)	\(1,30\pm0,07\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	5,5	"	\(1,52\pm0,08\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	5,0	"	\(1,46\pm0,05\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	4,5	"	\(1,69\pm0,05\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	4,1	\(d-\mathrm{Be}\)		\(1,79\pm0,08\)		\(^{26}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	4,0	\(d-\mathrm D\)	\(1,70\pm0,07\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	\(>3,5\)	—			\(0,3—0,2\)	\(^{19}\ n^{1}+\mathrm D^{2}=p^{1}+2n^{1}\)
\(^{1}\mathrm D\)	3,5	\(d-\mathrm D\)	\(2,04\pm0,07\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	3,0	"	\(2,24\pm0,09\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	\(2,88\pm0,04\)	"	\(2,17\pm0,08\)			\(^{39}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	\(2,8—2,1\)	"	\(2,10\ldots2,25\pm1,0\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	2,6	"	\(2,34\pm0,06\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	\(2,50—2,38\)	"	\(1,98\pm0,1\)			\(^{37}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	2,0	"	\(2,60\pm0,08\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	1,6	\(d-\mathrm C\)	\(2,90\pm0,12\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	\(1,0\pm0,1\)	"	\(3,11\pm0,20\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	0,97	\(p-\mathrm{Li}\)	\(2,97\pm0,14\)			\(^{38}\ \mathrm D_2\mathrm O\)
\(^{1}\mathrm D\)	0,72	"	\(3,46\pm0,13\)			\(^{38}\ \mathrm D_2\mathrm O\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
1 D	0.46	\(p-\mathrm{Li}\)	\(3.32 \pm 0.16\)			\(^{38}\ \mathrm{D_2O}\)
1 D	0.35	"	\(3.53 \pm 0.32\)			\(^{38}\ \mathrm{D_2O}\)
1 D	Slow	—	4.0			\(^{19}\)
1 D	"	—	5.3			\(^{20}\)
1 D	"	—		7		\(^{19}\)
1 D	Thermal	—		5.7		\(^{19,43}\)
1 D	"	—			\((1.1 \pm 2.3)\cdot 10^{-3}\)	\(^{19}\)
1 D	"	—			\((2–3)\cdot 10^{-4}\)	\(^{19}\quad n^{1}+\mathrm{D}^{2}=\mathrm{H}^{3}+\gamma\)
2 He	5.9	—				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.1\)
2 He	4.3	\(d-\mathrm{Be}\)				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.3 \pm 0.5\)
2 He	4.1	"				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.2 \pm 0.5\)
2 He	3.8	"				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=0.8 \pm 0.2\)
2 He	3.6	"				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.4 \pm 0.3\)
2 He	2.5	"				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.41 \pm 0.18\)
2 He	2.5	\(d-\mathrm{D}\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})\simeq 1.4\)
2 He	2.4	\(d-\mathrm{Be}\)				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H})=1.8 \pm 0.4\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
\({}^{2}\mathrm{He}\)	\(\sim 2.35\)	\(d—D\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 1.8\)
\({}^{2}\mathrm{He}\)	\(2.2\)	\(d—Be\)				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = 1.4 \pm 0.3\)
\({}^{2}\mathrm{He}\)	\(\sim 2.15\)	\(d—D\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 1.7\)
\({}^{2}\mathrm{He}\)	\(\sim 1.9\)	”				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 2.4\)
\({}^{2}\mathrm{He}\)	\(\sim 1.7\)	”				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 2.0\)
\({}^{2}\mathrm{He}\)	\(1.6\)	\(p—Li\)	\(4.60\)			\(^{42}\)
\({}^{2}\mathrm{He}\)	\(\sim 1.5\)	\(d—D\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 4.9\)
\({}^{2}\mathrm{He}\)	\(1.35\)	\(p—Li\)	\(5.66;\ 5.22\)			\(^{42}\)
\({}^{2}\mathrm{He}\)	\(\sim 1.3\)	\(d—D\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 4.3\)
\({}^{2}\mathrm{He}\)	\(1.25\)	\(p—Li\)	\(6.96;\ 6.70\)			\(^{42}\)
\({}^{2}\mathrm{He}\)	\(1.2\)	\(d—Be\)				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = 6.5 \pm 0.8\)
\({}^{2}\mathrm{He}\)	\(\sim 1.1\)	\(d—D\)				\(^{41}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = \sim 8.6\)
\({}^{2}\mathrm{He}\)	\(1.1\)	\(p—Li\)	\(6.35\)			\(^{42}\)
\({}^{2}\mathrm{He}\)	\(1.0\)	”	\(6.42;\ 6.75;\ 6.16\)			\(^{42}\)
\({}^{2}\mathrm{He}\)	\(1.0\)	\(d—Be\)				\(^{40}\ \sigma_{\mathrm{o.r.}}(\mathrm{He}):\sigma_{\mathrm{o.r.}}(\mathrm{H}) = 9.5 \pm 1.4\)

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
\(2\ \mathrm{He}\)	\(\sim 0.8\)	\(d-D\)				\(^{41}\ \sigma_{\text{o.p.}}(\mathrm{He}):\sigma_{\text{o.p.}}(\mathrm{H}) = \simeq 7.0\)
	\(0.8\)	\(p-\mathrm{Li}\)	\(4.91;\ 4.63;\ 4.28\)			\(^{42}\)
	\(\sim 0.65\)	\(d-D\)				\(^{41}\ \sigma_{\text{o.p.}}(\mathrm{He}):\sigma_{\text{o.p.}}(\mathrm{H}) = \simeq 7.0\)
	\(0.6\)	\(p-\mathrm{Li}\)	\(2.48\)			\(^{42}\)
	\(0.5\)	\(d-\mathrm{Be}\)				\(^{40}\ \sigma_{\text{o.p.}}(\mathrm{He}):\sigma_{\text{o.p.}}(\mathrm{H}) = \simeq 0.4 \pm 0.2\)
	Thermal	—	\(1.51\)			\(^{19}\ 300^\circ\) abs.
\(3\ \mathrm{Li}\)	—	\(d-\mathrm{Li}\)	\(2.64 \pm 0.18\)			\(^{37}\ \mathrm{Li}_2\mathrm{CO}_3\)
	\(2.50\text{–}2.38\)	\(d-D\)	\(2.01 \pm 0.21\)			\(^{37}\ \mathrm{Li}_2\mathrm{CO}_3\)
	\(0.860\)	\(\mathrm{RaTh}\ \gamma-\mathrm{Be}\)	\(2.3 \pm 0.5\)			\(^{31}\)
	\(0.210\)	\(\mathrm{RaTh}\ \gamma-D\)	\(2.2 \pm 0.4\)			\(^{31}\)
	\(0.18\) or \(0.10\)	\(d-C\)	\(2.0\)			\(^{44}\)
	\(0.15\)	\(\mathrm{RaC}\ \gamma-\mathrm{Be}\)		\(1.0 \pm 0.3\)		\(^{45}\)
	\(250\text{–}0.02\ \mathrm{eV}\)	—	\(11.5\,E_n^{-1/2} + 1.7\)			\(^{46}\ E_n\) in eV
	Slowed	—	\(58\)			\(^{20}\)
	*	—	\(45\)			\(^{20}\)
	*	—			\(58\)	\(^{20}\)
	Thermal	—			\(900\)	\(^{19}\ \mathrm{Li}^6 + n^1 = \mathrm{He}^4 + \mathrm{H}^3\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
\(4\ \mathrm{Fe}\)	0.860	RaTh \(\gamma\)—Be	\(1.7\pm0.2\)			31
\(4\ \mathrm{Fe}\)	0.860	RaTh \(\gamma\)—Be	\(2.32\pm0.20\)			29
\(4\ \mathrm{Fe}\)	0.83	Na\(^ {24}\) \(\gamma\)—Be	3.1			47
\(4\ \mathrm{Fe}\)	0.62	La\(^ {140}\) \(\gamma\)—Be	3.3			47
\(4\ \mathrm{Fe}\)	0.22	Na\(^ {24}\) \(\gamma\)—D\(_2\)O	4.2			47
\(4\ \mathrm{Fe}\)	0.210	RaTh \(\gamma\)—D	\(2.8\pm0.2\)			31
\(4\ \mathrm{Fe}\)	0.18 or 0.10	\(d\)—C	2.6	\(2.9\pm0.5\)		44
\(4\ \mathrm{Fe}\)	0.15	RaC \(\gamma\)—Be				45
\(4\ \mathrm{Fe}\)	0.14	Mn\(^ {56}\) \(\gamma\)—Be	4.3			47
\(4\ \mathrm{Fe}\)	0.13	Ga\(^ {72}\) \(\gamma\)—D\(_2\)O	4.3			47
\(4\ \mathrm{Fe}\)	0.024	Sb\(^ {124}\) \(\gamma\)—Be	5.0			47
\(4\ \mathrm{Fe}\)	D	—	6.10			48
\(4\ \mathrm{Fe}\)	0.2–0.01 eV	—		\(\sim 5.4\)		49
\(4\ \mathrm{Fe}\)	Slow	—	5.3			19
\(4\ \mathrm{Fe}\)	”	—		6.9		19
\(4\ \mathrm{Fe}\)	”	—			\(<0.03\)	20
\(4\ \mathrm{Fe}\)	Therm.	—		6.1	0.0085	50
\(4\ \mathrm{Fe}\)	”	—			\(<0.01\)	61 Order of magnitude, \(\sigma_{\mathrm{capture}}\)
\(5\ \mathrm{B}\)	—	\(d\)—Li	\(2.15\pm0.13\)			\(\varphi\) 87 B\(_2\)O\(_3\)
\(5\ \mathrm{B}\)	3	\(d\)—D		1.6		51
\(5\ \mathrm{B}\)	\(2.88\pm0.04\)	”	\(1.98\pm0.07\)			39 B\(_4\)C
\(5\ \mathrm{B}\)	2.8–2.1	”	\(1.86\ldots2.27\pm0.18\)			28
\(5\ \mathrm{B}\)	2.5	”		1.65		37
\(5\ \mathrm{B}\)	2.50–2.38	”	\(1.65\pm0.15\)			37 B\(_2\)O\(_3\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
5 B	1.5	\(p-\mathrm{Li}\)		1.9		51
5 B	1.2	”		2.0		51
5 B	1.0	”		1.6		51
5 B	0.86	\(\mathrm{RaTh}\ \gamma-\mathrm{Be}\)		\(2.9\pm0.3\)		33, 52
5 B	0.83	\(\mathrm{Na}^{24}\ \gamma-\mathrm{Be}\)	2.3			47 \( \mathrm{B}_4\mathrm{C}\)
5 B	0.8	\(p-\mathrm{Li}\)		1.8		51
5 B	0.6	”		2.4		51
5 B	0.22	\(\mathrm{Na}^{24}\ \gamma-\mathrm{D}_2\mathrm{O}\)	4.3			47
5 B	0.210	\(\mathrm{RaTh}\ \gamma-\mathrm{D}\)		\(4.2\pm0.5\)		33
5 B	0.2	\(p-\mathrm{Li}\)		3.5		51
5 B	0.15	\(\mathrm{RaC}\ \gamma-\mathrm{Be}\)		\(3.8\pm0.5\)		46
5 B	0.14	\(\mathrm{Mn}^{56}\ \gamma-\mathrm{Be}\)	4.7			47
5 B	0.13	\(\mathrm{Ga}^{72}\ \gamma-\mathrm{D}_2\mathrm{O}\)	4.9			47
5 B	0.024	\(\mathrm{Sb}^{124}\ \gamma-\mathrm{Be}\)	5.5			47
5 B	\(1000–0.01\ \mathrm{eV}\)	—		4.2	\((1.61\pm0.2)\dfrac{1}{v}\) or \((116\pm1.5)E_n^{-1/2}\)	53, 54 \(v\) in \(\dfrac{\mathrm{m}}{\mu\mathrm{sec}}\)
5 B	\(250–0.01\ \mathrm{eV}\)	—	\((118\pm4)E_n^{-1/2}\)			55
5 B	Slow	—	350			19
5 B	”	—	503			20
5 B	”	—	\(550–570\)			20
5 B	”	—			600	20
5 B	”	—			500	20
5 B	”	—			3000	19 \(\mathrm{B}^{10}+n^1=\mathrm{Li}^7+\mathrm{He}^4\)
5 B	Thermal	—	708			56
5 B	”	—			703	57

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
6 C	25,4	\(d\)—Li	1,05			58
6 C	21,1	\(d\)—Li	\(1,17 \pm 0,12\)			25
6 C	19,6	\(d\)—Li	\(1,31 \pm 0,10\)			25
6 C	18,0	\(d\)—Li	\(1,13 \pm 0,23\)			25
6 C	16,5	\(d\)—Li	\(1,29 \pm 0,14\)			25
6 C	\(\sim 15\)	\(d\)—Li	1,13			19
6 C	—	\(d\)—Li	\(1,27 \pm 0,04\)			37
6 C	15	\(d\)—Li			\(\geq 0,018\)	19 \( \mathrm{C}^{12}+n^1=\begin{cases}3\mathrm{He}^4+n^1\\ \mathrm{C}^{11}+2n^1\end{cases}\)
6 C	14,8	\(d\)—Li	\(1,24 \pm 0,16\)			25
6 C	13,5	\(d\)—Li				26
6 C	12,9	\(d\)—Li	\(1,18 \pm 0,12\)			25
6 C	12,5	\(d\)—B		\(1,10 \pm 0,12\)		26
6 C	10,6	\(d\)—Li	\(1,43 \pm 0,14\)			28
6 C	9,3	\(d\)—Be	\(1,45 \pm 0,14\)			25
6 C	7,8	\(d\)—Be	\(1,51 \pm 0,21\)			25
6 C	6,5	\(d\)—Be	\(1,51 \pm 0,15\)			45
6 C	6,0	\(d\)—D		\(1,11 \pm 0,10\)		27
6 C	5,5	\(d\)—D		\(1,07 \pm 0,04\)		27
6 C	5,0	\(d\)—D		\(1,18 \pm 0,03\)		27
6 C	4,75	\(d\)—D		\(1,60 \pm 0,15\)		27
6 C	4,5	\(d\)—D		\(1,93 \pm 0,06\)		27
6 C	4,25	\(d\)—D		\(2,16 \pm 0,07\)		27
6 C	4,1	\(d\)—Be		\(1,99 \pm 0,04\)		26
6 C	4,0	\(d\)—D		\(1,85 \pm 0,10\)		52
6 C	3,75	\(d\)—D		\(2,43 \pm 0,12\)		27
6 C	3,5	\(d\)—D		\(2,39 \pm 0,09\)		27
6 C	3,25	\(d\)—D		\(1,69 \pm 0,13\)		27
6 C	3,1	\(d\)—D		0,79 and 0,19		59 Back scatt.

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
\(6\ \mathrm{C}\)	3.0	\(d-\mathrm{D}\)		\(1.59 \pm 0.05\)		27
\(6\ \mathrm{C}\)	\(2.88 \pm 0.04\)	”	\(1.97 \pm 0.07\)			89
\(6\ \mathrm{C}\)	2.85	”		\(1.57 \pm 0.11\)		27
\(6\ \mathrm{C}\)	2.8	”	1.57			19
\(6\ \mathrm{C}\)	\(2.7–2.2\)	”	1.50			19
\(6\ \mathrm{C}\)	2.65	”	1.45			19
\(6\ \mathrm{C}\)	2.6	”		\(1.60 \pm 0.03\)		27
\(6\ \mathrm{C}\)	2.57	”	1.38			19
\(6\ \mathrm{C}\)	2.5	”	\(1.6 \pm 0.3\)	\(2.0 \pm 0.2\ (45^\circ)\)		80
\(6\ \mathrm{C}\)	2.5	”		\(1.2 \pm 0.2\ (100^\circ)\)		60; elastic scat.
\(6\ \mathrm{C}\)	\(2.50–2.38\)	”	\(1.50 \pm 0.04\)			37
\(6\ \mathrm{C}\)	2.49	”	1.33			19
\(6\ \mathrm{C}\)	2.41	”	1.39			19
\(6\ \mathrm{C}\)	2.34	”	1.41			19
\(6\ \mathrm{C}\)	2.0	”		\(1.63 \pm 0.04\)		27
\(6\ \mathrm{C}\)	1.6	\(d-\mathrm{C}\)		\(1.90 \pm 0.05\)		27
\(6\ \mathrm{C}\)	\(1.0 \pm 0.1\)	”		\(2.38 \pm 0.09\)		27
\(6\ \mathrm{C}\)	0.97	\(p-\mathrm{Li}\)		\(2.40 \pm 0.03\)		27
\(6\ \mathrm{C}\)	0.860	\(\mathrm{RaTh}\ \gamma-\mathrm{Be}\)	\(2.66 \pm 0.20\)			29
\(6\ \mathrm{C}\)	0.860	”	\(3.3 \pm 0.4\)			31
\(6\ \mathrm{C}\)	0.83	\(\mathrm{Na}^{24}\gamma-\mathrm{Be}\)	2.9			47
\(6\ \mathrm{C}\)	0.72	\(p-\mathrm{Li}\)		\(2.49 \pm 0.06\)		27
\(6\ \mathrm{C}\)	0.62	\(\mathrm{La}^{140}\gamma-\mathrm{Be}\)	3.3			47
\(6\ \mathrm{C}\)	0.490	\(p-\mathrm{Li}\)	\(3.26 \pm 0.10\)			32
\(6\ \mathrm{C}\)	0.46	”		\(3.15 \pm 0.10\)		27
\(6\ \mathrm{C}\)	0.35	”		\(3.15 \pm 0.08\)		27
\(6\ \mathrm{C}\)	0.265	”	\(3.85 \pm 0.09\)			32
\(6\ \mathrm{C}\)	0.22	\(\mathrm{Na}^{24}\gamma-\mathrm{D}_2\mathrm{O}\)	4.1			47
\(6\ \mathrm{C}\)	0.210	\(\mathrm{RaTh}\ \gamma-\mathrm{D}\)	\(4.7 \pm 0.5\)			31

Continuation

Element	$E_n$ in MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scatt}}$	$\sigma_{\mathrm{capt}}$	Note
6 C	0.18 or 0.10	$d$—C	2.1			44
6 C	0.15	RaC$\gamma$—Be		$1.5 \pm 0.3$		45
6 C	0.14	Mn$^{56}\gamma$—Be	4.3			47
6 C	0.13	Ga$^{72}\gamma$—D$_2$O	4.3			47
6 C	0.095	—Li$p$	$4.65 \pm 0.14$			32
6 C	0.035	”	$4.63 \pm 0.19$			32
6 C	0.024	Sb$^{124}\gamma$—Be	4.6			47
6 C	$J$	—	4.80			19
6 C	$D$	—		$3.0 \pm 0.3$		19
6 C	$D$	—	4.84			48
6 C	1–0.5 eV	—	4.8			19
6 C	$C$	—		3.6		19
6 C	Slow	—	4.83	4.83		19
6 C	”	—	4.1			19
6 C	”	—		4.5		20
6 C	”	—			$<0.06$	20
6 C	”	—			$<0.01$	20
6 C	Thermal	—			0.003	19
6 C	”	—		4.8	0.0049	50
6 C	”	—			$<0.01$	61 Order of magnitude, $\sigma_{\mathrm{capt}}$
7 N	—	$d$—Li	$2.16 \pm 0.20$			37 N$_2$Mg$_3$
7 N	$2.88 \pm 0.04$	$d$—D	$1.38 \pm 0.06$			39
7 N	2.8	”	1.25			19 NaN$_3$
7 N	2.8	”			0.163	19 N$^{14}+n^1=\mathrm{B}^{11}+\mathrm{He}^4$
7 N	2.8	”			0.04	19 N$^{14}+n^1=\mathrm{C}^{14}+p^1$

Continuation

Element	$E_n$ in MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scat}}$	$\sigma_{\mathrm{abs}}$	Note
7 N	2,8—2,1	$d$–D	1,83…2,55±0,3			²⁸ $N_2Mg_3$
7 N	2,7—2,2	$d$–D	1,3			¹⁹
7 N	2,65	$d$–D	1,28			¹⁹ $NaN_3$
7 N	2,57	$d$–D	1,39			¹⁹
7 N	2,50—2,38	$d$–D	1,56±0,22			³⁷ $N_2Mg_3$
7 N	2,49	$d$–D	1,27			¹⁹ $NaN_3$
7 N	2,41	$d$–D	1,22			¹⁹ $NaN_3$
7 N	2,34	$d$–D	1,33			¹⁹ $NaN_3$
7 N	—	$d$–D		0,97	0,2	¹⁰
7 N	∼1,68	$p$–Li			∼0,01	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,68	$p$–Li			∼0,036	⁶² $N^{14}+n^1=B^{11}+He^4$
7 N	∼1,59	$p$–Li			∼0,01	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,59	$p$–Li			∼0,036	⁶² $N^{14}+n^1=B^{11}+He^4$
7 N	∼1,54	$p$–Li			∼0,019	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,50	$p$–Li			∼0,049	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,50	$p$–Li			∼0,092	⁶² $N^{14}+n^1=B^{11}+He^4$
7 N	∼1,45	$p$–Li			∼0,113	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,45	$p$–Li			∼0,116	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,40	$p$–Li			∼0,074	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,40	$p$–Li			∼0,014	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,30	$p$–Li			∼0,012	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,30	$p$–Li			∼0,016	⁶² $N^{14}+n^1=B^{11}+He^4$
7 N	∼1,25	$p$–Li			∼0,014	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,20	$p$–Li			∼0,012	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,20	$p$–Li			∼0,016	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,10	$p$–Li			∼0,011	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼1,00	$p$–Li			∼0,012	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼0,97	$p$–Li			∼0,008	⁶² $N^{14}+n^1=C^{14}+p^1$
7 N	∼0,94	$p$–Li			∼0,012	⁶² $N^{14}+n^1=C^{14}+p^1$

Continuation

Element	$E_n$ in MeV	Neutron source	$\sigma$	$\sigma_{\text{scatt}}$	$\sigma_{\text{tot}}$	Note
7 N	$\sim 0.88$	$p$—Li			$\sim 0.017$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.84$	same			$\sim 0.026$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.82$	same			$\sim 0.029$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.80$	same			$\sim 0.026$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.75$	same			$\sim 0.079$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.73$	same			$\sim 0.136$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.70$	same			$\sim 0.130$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.69$	same			$\sim 0.169$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.60$	same			$\sim 0.051$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.59$	same			$\sim 0.046$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.55$	same			$\sim 0.063$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.51$	same			$\sim 0.023$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.45$	same			$\sim 0.002$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.39$	same			$\sim 0.002_5$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.33$	same			$\sim 0.002_5$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.25$	same			$\sim 0.002_5$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$\sim 0.20$	same			$\sim 0.002_5$	${}^{62}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$
7 N	$0.18$ or $0.10$	$d$—C	$2.1$			${}^{44}$
7 N	$0.15$	RaC—Be		$1.6 \pm 0.3$		${}^{45}$
7 N	C	—			$<0.2$	${}^{63}$ $\mathrm{N}^{15}$
7 N	*	—			$<0.01$	${}^{64}$ $\mathrm{N}^{15}$
7 N	Slow	—	$11.3$			${}^{19}$ $\mathrm{AlN}_3$
7 N	same	—	$8.2$			${}^{19}$ $\mathrm{AlN}_3$
7 N	*	—			$1.05$	${}^{20}$ $\mathrm{NH}_4\mathrm{NO}_3$
7 N	Thermal	—			$1.2$	${}^{20}$ $\mathrm{NH}_4\mathrm{NO}_3$
7 N	same	—	$12$			${}^{19}$ $\sim 300^\circ$ abs.
7 N	*	—			$1.3 \pm 0.3$	${}^{19}$
7 N	same	—			$1.4$	${}^{65}$ $\mathrm{N}^{14}+n^1=\mathrm{C}^{14}+p^1$

Continuation

Element	$E_n$, MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scatt}}$	$\sigma_{\mathrm{abs}}$	Note
$_8$ O	—	$d$—Li	1,41±0,0			³⁷ SiO₂
$_8$ O	6,0	$d$—D	1,04±0,08			³⁸ D₂O, H₂O
$_8$ O	5,5	$d$—D	0,96±0,08			³⁸ D₂O, H₂O
$_8$ O	5,0	$d$—D	1,66±0,09			³⁸ D₂O, H₂O
$_8$ O	4,5	$d$—D	1,83±0,16			³⁸ D₂O, H₂O
$_8$ O	4,0	$d$—D	2,90±0,09			³⁸ D₂O, H₂O
$_8$ O	3,5	$d$—D	2,39±0,12			³⁸ D₂O, H₂O
$_8$ O	3,0	$d$—D	0,96±0,09			³⁸ D₂O, H₂O
$_8$ O	2,88±0,04	$d$—D	1,25±0,05			³⁹
$_8$ O	2,8—2,1	$d$—D	1,14…1,29 ±0,07			²⁸ SiO₂
$_8$ O	2,6	$d$—D	1,09±0,11			³⁸ D₂O, H₂O
$_8$ O	2,50—2,38	$d$—D	1,41±0,07			³⁷ SiO₃
$_8$ O	2,0	$d$—D	0,89±0,12			³⁸ D₂O, H₂O
$_8$ O	1,6	$d$—C	1,43±0,1			³⁸ D₂O, H₂O
$_8$ O	1,0±0,1	$d$—C	3,86±0,35			³⁸ D₂O, H₂O
$_8$ O	0,97	$p$—Li	5,66±0,2			³⁸ D₂O, H₂O
$_8$ O	0,86	RaTh $\gamma$—Be	2,2±1,0			³¹ SiO₂
$_8$ O	0,83	Na²⁴ $\gamma$—Be	4,9			⁴⁷
$_8$ O	0,72	$p$—Li	2,01±0,20			³⁸ D₂O, H₂O
$_8$ O	0,62	La¹⁴⁰ $\gamma$—Be	3,5			⁴⁷
$_8$ O	0,46	$p$—Li	3,61±0,25			³⁸ D₂O, H₂O
$_8$ O	0,35	$p$—Li	1,80±0,53			³⁸ D₂O, H₂O
$_8$ O	0,22	Na²⁴ $\gamma$—D₂O	3,0			⁴⁷
$_8$ O	0,210	RaTh $\gamma$—D	3,0±1,0			³¹ SiO₂
$_8$ O	0,18 or 0,10	$d$—C	2,1			⁴⁴
$_8$ O	0,15	RaC $\gamma$—Be		1,8±0,4		⁴⁵
$_8$ O	0,14	Mn⁵⁶ $\gamma$—Be	4,1			⁴⁷
$_8$ O	0,13	Ga⁷² $\gamma$—D₂O	3,5			⁴⁷
$_8$ O	0,024	Sb¹²⁴ $\gamma$—Be	3,6			⁴⁷

Continuation

Element	\(E_n\), MeV	Neutron source	\(\varepsilon\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
8 O	\(D\)	—		3		\(^{19}\ \mathrm{Al_2O_3}\)
8 O	Slow	—	3.3			\(^{19}\ \mathrm{Al_2O_3}\)
8 O	"	—		4.2		\(^{19}\ \mathrm{Al_2O_3}\)
8 O	"	—	4.1			\(^{19}\)
8 O	Thermal	—			\(<0.01\)	\(^{20}\)
8 O	"	—			\(0.38 \pm 0.09\)	\(^{65}\ \mathrm{O}^{17}+n^1=\mathrm{C}^{14}+\mathrm{He}^4\)
8 O	"	—			\(2.2 \cdot 10^{-4}\)	\(^{66}\ \mathrm{O}^{18}+n^1=\mathrm{O}^{19}+\gamma\)
8 O	"	—			\(2 \cdot 10^{-4}\)	\(^{67}\ \mathrm{O}^{18}+n^1=\mathrm{O}^{19}+\gamma\)
9 F	—	\(d\) Li	\(1.37 \pm 0.11\)			\(^{37}\ \mathrm{CaF_2}\)
9 F	\(2.88 \pm 0.04\)	\(d-D\)	\(2.30 \pm 0.13\)			\(^{39}\ \mathrm{CaF_2}\)
9 F	\(2.8–2.4\)	"	\(2.40 \ldots 3.18 \pm 0.12\)			\(^{48}\ \mathrm{NaF}\)
9 F	0.56	RaTh \(\gamma\)—Be	\(3.7 \pm 1.0\)			\(^{31}\ \mathrm{CaF_2}\)
9 F	0.83	Na\(^{24}\) \(\gamma\)—Be	4.1			\(^{47}\ \mathrm{BeF_2}\)
9 F	0.62	La\(^{140}\) \(\gamma\)—Be	4.6			\(^{47}\ \mathrm{BeF_2}\)
9 F	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	6.9			\(^{47}\ \mathrm{BeF_2}\)
9 F	0.210	RaTh \(\gamma\)—D	\(6.4 \pm 1.3\)			\(^{31}\ \mathrm{CaF_2}\)
9 F	0.18 or 0.10	\(d-C\)	2.7			\(^{44}\ \mathrm{NaF}\)
9 F	0.15	RaC \(\gamma\)—Be		\(6.3 \pm 1.6\)		\(^{45}\)
9 F	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	5.7			\(^{47}\ \mathrm{BeF_2}\)
9 F	0.024	Sb\(^{124}\) \(\gamma\)—Be	3.5			\(^{47}\ \mathrm{BeF_2}\)
9 F	\(D\)	—	3.7			\(^{48}\ \mathrm{C_2F_{16}}\)
9 F	\(C\)	—			\(<0.05\)	\(^{69}\ \mathrm{F}^{19}\)
9 F	"	—			0.01	\(^{64}\)
9 F	Slow	—	4.1			\(^{19}\ \mathrm{CaF_2}\)

Continuation

Element	\(E_n\), MeV	Neutron source		\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
9 F	Slow	—	2.5			\(^{19}\) CaF\(_2\)
9 F	"	—			\(\sim 0.05\)	\(^{20}\)
9 F	Therm.	—			\(<0.5\)	\(^{19}\) NaF
9 F	"	—			\(\lesssim 0.01\)	\(^{61}\) Order of magnitude, \(\sigma_{\mathrm{capt}}\)
10 Ne	2.5	\(d-D\)			\(\sim 0.05\)	\(^{68}\) Ne\(^{20}+n^1=\)O\(^{17}+\)He\(^4\)
10 Ne	Therm.	—	2.94			\(^{19}\) 300° abs.
11 Na	—	\(d-\)Li	\(2.35\pm0.09\)			\(^{37}\)
11 Na	\(2.88\pm0.04\)	\(d-D\)	\(2.37\pm0.09\)			\(^{39}\)
11 Na	2.8	"	2.38			\(^{19}\)
11 Na	\(2.8-2.1\)	"	\(2.8\ldots3.18\pm0.12\)			\(^{28}\)
11 Na	\(2.7-2.2\)	"	2.6			\(^{19}\)
11 Na	2.65	"	2.50			\(^{19}\)
11 Na	2.57	"	2.63			\(^{19}\)
11 Na	\(2.51-2.33\)	"	\(3.33\pm0.09\)			\(^{37}\)
11 Na	2.49	"	2.69			\(^{19}\)
11 Na	2.41	"	2.69			\(^{19}\)
11 Na	2.34	"	2.74			\(^{19}\)
11 Na	\(0.8\cdot0\)	RaTh \(\gamma-\)Be	\(3.3\pm0.7\)			\(^{31}\)
11 Na	0.83	Na\(^{24}\gamma-\)Be	4.6			\(^{47}\) NaJ
11 Na	0.62	La\(^{140}\gamma-\)Be	5.9			\(^{47}\) NaJ
11 Na	0.22	Na\(^{24}\gamma-\)D,O	3.8			\(^{47}\) NaJ
11 Na	0.210	RaTh \(\gamma-\)D	\(3.2\pm0.6\)			\(^{31}\)
11 Na	0.18 or 0.10	\(d-C\)	3.4			\(^{44}\)

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
11 Na	0.15	RaC \(\gamma\)—Be		\(3.5 \pm 0.8\)		\(^{45}\)
11 Na	0.14	Mn\(^{56}\) \(\gamma\)—Be	4.2			\(^{47}\) NaJ
11 Na	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	3.9			\(^{47}\) NaJ
11 Na	0.024	Sb\(^{124}\) \(\gamma\)—Be	5.1			\(^{47}\) NaJ
11 Na	\(D\)	—		\(\sim 4.7\)		\(^{19}\) Na\(_2\)S
11 Na	\(C\)	—			0.4	\(^{63}\) Na\(^{23}\)
11 Na	"	—			0.35	\(^{69}\)
11 Na	Slow	—	4.2			\(^{19}\) NaF
11 Na	*	—		3.6		\(^{19}\) NaF
11 Na	*	—			0.38	\(^{20}\) Na\(_2\)CO\(_3\)
11 Na	*	—			\(0.47 \pm 0.04\)	\(^{70}\) NaF
11 Na	*	—			16	\(^{19}\) NaCl
11 Na	Thermal	—			\(<0.5\)	\(^{19}\) NaF
12 Mg	—	\(d\)—Li	\(1.79 \pm 0.07\)			\(^{37}\)
12 Mg	\(2.88 \pm 0.04\)	\(d\)—D	\(2.85 \pm 0.07\)			\(^{39}\)
12 Mg	2.8	"	2.34			\(^{19}\)
12 Mg	\(2.8 \to 2.1\)	"	\(1.94 \ldots 2.02 \pm 0.10\)			\(^{28}\)
12 Mg	2.65	"	2.04			\(^{19}\)
12 Mg	2.57	"	2.14			\(^{19}\)
12 Mg	2.5	"		\(\sim 1.6\) (elastic)		\(^{71}\)
12 Mg	2.5	"		\(\sim 0.6\) (inelastic)		\(^{71}\)
12 Mg	\(2.50—2.38\)	"	\(1.89 \pm 0.07\)			\(^{19}\)
12 Mg	2.49	"	1.76			\(^{19}\)
12 Mg	2.41	"	1.94			\(^{19}\)
12 Mg	2.34	"	2.19			\(^{19}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
\(^{12}\mathrm{Mg}\)	0,860	RaTh \(\gamma\)—Be	\(3,6 \pm 0,4\)			81
\(^{12}\mathrm{Mg}\)	0,83	Na\(^{24}\gamma\)—Be	3,4			47
\(^{12}\mathrm{Mg}\)	0,62	La\(^{140}\gamma\)—Be	4,2			47
\(^{12}\mathrm{Mg}\)	0,22	Na\(^{24}\gamma\)—D\(_2\)O	8,7			47
\(^{12}\mathrm{Mg}\)	0,210	RaTh \(\gamma\)—D	\(3,9 \pm 0,4\)			81
\(^{12}\mathrm{Mg}\)	0,18 or 0,10	\(d\)—C	3,3			19
\(^{12}\mathrm{Mg}\)	0,15	RaC \(\gamma\)—Be		\(8,4 \pm 2,8\)		45
\(^{12}\mathrm{Mg}\)	0,14	Mn\(^{56}\gamma\)—Be	5,7			47
\(^{12}\mathrm{Mg}\)	0,13	Ga\(^{72}\gamma\)—D\(_2\)O	4,9			47
\(^{12}\mathrm{Mg}\)	0,024	Sb\(^{124}\gamma\)—Be	4,4			47
\(^{12}\mathrm{Mg}\)	\(D\)	—		\(6,8 \pm 0,7\)		19
\(^{12}\mathrm{Mg}\)	\(C\)	—		3,3		19
\(^{12}\mathrm{Mg}\)		—			0,3	83 Mg\(^{25}\)
\(^{12}\mathrm{Mg}\)	Slow	—		4,2		19
\(^{12}\mathrm{Mg}\)	"	—	3,5			19
\(^{12}\mathrm{Mg}\)	"	—			0,31	90
\(^{12}\mathrm{Mg}\)	"	—			0,22	90
\(^{12}\mathrm{Mg}\)	"	—			\(0,27 \pm 0,02\)	70
\(^{13}\mathrm{Al}\)	—	\(d\)—Li	\(2,12 \pm 0,05\)			57
\(^{13}\mathrm{Al}\)	3,1	\(d\)—D		0,66–0,53		59 Backward elastic scattering
\(^{13}\mathrm{Al}\)	\(2,88 \pm 0,04\)		\(2,34 \pm 0,07\)			59
\(^{13}\mathrm{Al}\)	2,80	"	2,48			19
\(^{13}\mathrm{Al}\)	2,8–2,1	"	\(2,35 \cdot 2,66 \pm 0,07\)			83
\(^{13}\mathrm{Al}\)	2,65	"	2,94			19
\(^{13}\mathrm{Al}\)	2,57	"	2,91			19
\(^{13}\mathrm{Al}\)	2,5	"	\(2,4 \pm 0,3\)	\(3,8 \pm 0,2\) \((45^\circ)\)		60

Continuation

Element	$E_n$, MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scat}}$	$\sigma_{\mathrm{abs}}$	Note
13 Al	2.5	$d-D$		2.5 (100°)		60
13 Al	2.5	*		$3.4 \pm 0.5$ (45°) elastic scat.		60
13 Al	2.5	”		$1.1 \pm 0.2$ (100°) elastic scat.		6 Elastic scat.
13 Al	2.50–2.38	”	$3.15 \pm 0.11$			19
13 Al	2.49	”	2.18			19
13 Al	2.41	*	2.19			19
13 Al	2.34	*	2.49			19
13 Al	0.88	$p-Li$	3.9			72
13 Al	0.860	RaTh $\gamma-Be$	$3.1 \pm 0.4$			31
13 Al	0.860	”	$3.39 \pm 0.25$			29
13 Al	0.83	Na24 $\gamma-Be$	3.5			47
13 Al	0.83	$p-Li$	4.1			72
13 Al	0.62	La140 $\gamma-Be$	4.1			47
13 Al	0.62	$p-Li$	2.7			72
13 Al	0.60	”	3.0			72
13 Al	0.22	Na24 $\gamma-D_2O$	3.2		$3 \cdot 10^{-4}$	47
13 Al	$0.22 \pm 0.04$	ThC″ $\gamma-D$				19
13 Al	0.22	$p-Li$	5.2			72
13 Al	0.210	RaTh $\gamma-D$	$3.8 \pm 0.4$			81
13 Al	0.20	$p-Li$	4.0			72
13 Al	0.18 or 0.10	$d-C$	3.7	$4.0 \pm 0.4$	$<0.15$	19 78
13 Al	0.15	RaC $\gamma-Be$				47
13 Al	0.14	Mn56 $\gamma-Be$	3.2			47
13 Al	0.13	Ga72 $\gamma-D_2O$	5.3			47
13 Al	0.13	$p-Li$	3.7			72
13 Al	0.024	Sb124 $\gamma-Be$	0.8			47

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
13 Al	0.024	\(p\)—Li	1.0			72
13 Al	\(D\)	—		\(1.5 \pm 0.3\)		19
13 Al	″	—	1.46			48
13 Al	\(C\)	—	1.6			19
13 Al	″	—			0.2	66 Al\(^{27}\)
13 Al	″	—			0.21	66 Al\(^{27}\)
13 Al	Slow	—	1.5			19
13 Al	″	—		1.6		19
13 Al	″	—			0.42	20
13 Al	″	—			0.44	20
13 Al	″	—			\(0.19 \pm 0.01\)	70
14 Si	—	\(d\)—Li	\(2.00 \pm 0.05\)			37
14 Si	\(2.88 \pm 0.04\)	\(d\)—D	\(2.77 \pm 0.08\)			30
14 Si	\(2.8 \pm 2.1\)	″	\(2.55 \ldots 2.88 \pm 0.07\)			98
14 Si	\(2.50—2.38\)	″	\(2.95 \pm 0.06\)			37
14 Si	\(0.86^{1)}\)	RaTh \(\gamma\)—Be	\(4.4 \pm 0.6\)			31
14 Si	0.210	RaTh \(\gamma\)—D	\(7.2 \pm 0.9\)			31
14 Si	0.18 or 0.10	\(d\)—C	3.2			44
14 Si	0.15	RaC \(\gamma\)—Be		\(1.4 \pm 0.7\)		45
14 Si	\(D\)	—		\(4.2 \pm 0.4\)		19
14 Si	\(C\)	—	\(3.2 \pm 1.2\)			19 SiO\(_2\)
14 Si	″	—	\(3.0 \pm 0.7\)			19 SiO\(_2\)
14 Si	″	—			\(<0.5\)	63 Si\(^{30}\)
14 Si	Resonance neutrons	—	\(7.2 \pm 1.2\)			19 SiO\(_2\)
14 Si	Slow	—	2.5			19

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
\(^{14}\mathrm{Si}\)	Slow	—	\(4.1—4.5\pm0.6\)			^19^ \(\mathrm{SiO_2}\)
\(^{14}\mathrm{Si}\)	*	—		\(1.7\)		^19^
\(^{14}\mathrm{Si}\)	*	—			\(<0.06\)	^20^
\(^{14}\mathrm{Si}\)	Thermal	—	\(2.3\pm0.7\)			^19^ \(\mathrm{SiO_2}\)
\(^{14}\mathrm{Si}\)	*	—			\(\simeq 0.01\)	^61^ Order of magnitude, \(\sigma_{\mathrm{capture}}\)
\(^{15}\mathrm{P}\)	—	\(d\)—Li	\(2.82\pm0.10\)			^87^
\(^{15}\mathrm{P}\)	\(2.8—2.1\)	\(d\)—D	\(2.71\ldots3.12\pm0.09\)			^28^
\(^{15}\mathrm{P}\)	\(2.50—2.38\)	*	\(3.24\pm0.08\)			^37^
\(^{15}\mathrm{P}\)	\(0.860\)	RaTh \(\gamma\)—Be	\(1.8\pm0.7\)			^31^
\(^{15}\mathrm{P}\)	\(0.83\)	Na\(^ {24}\gamma\)—Be	\(3.5\)			^47^
\(^{15}\mathrm{P}\)	\(0.62\)	La\(^ {140}\gamma\)—Be	\(3.1\)			^47^
\(^{15}\mathrm{P}\)	\(0.22\)	Na\(^ {24}\gamma\)—D\(_2\)O	\(3.2\)			^47^
\(^{15}\mathrm{P}\)	\(0.210\)	RaTh \(\gamma\)—D	\(2.4\pm0.4\)			^31^
\(^{15}\mathrm{P}\)	\(0.18\) or \(0.10\)	\(d\)—C	\(4.4\)			^44^
\(^{15}\mathrm{P}\)	\(0.14\)	Mn\(^ {56}\gamma\)—Be	\(3.1\)			^47^
\(^{15}\mathrm{P}\)	\(0.13\)	Ga\(^ {72}\gamma\)—D\(_2\)O	\(3.1\)			^47^
\(^{15}\mathrm{P}\)	\(0.024\)	Sb\(^ {124}\gamma\)—Be	\(3.8\)			^47^
\(^{15}\mathrm{P}\)	\(D\)	—		\(9.1\pm0.9\)		^19^
\(^{15}\mathrm{P}\)	\(C\)	—			\(0.3\)	^63^ P31
\(^{15}\mathrm{P}\)	*	—			\(\sim0.2\)	^69^ P31
\(^{15}\mathrm{P}\)	Slow	—	\(13.6\)			^19^
\(^{15}\mathrm{P}\)	*	—	\(14.7\)			^19^
\(^{15}\mathrm{P}\)	*	—		\(10.4\)		^19^
\(^{15}\mathrm{P}\)	*	—			\(0.23\)	^20^
\(^{15}\mathrm{P}\)	Thermal	—	—		\(1.0\)	^19^ \(\mathrm{H_3PO_4}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
16 S	—	\(d\)—Li	\(2.23 \pm 0.09\)			37
16 S	\(2.88 \pm 0.04\)	\(d\)—D	\(3.12 \pm 0.15\)			39
16 S	\(2.8—2.1\)	”	\(2.50 \ldots 2.68 \pm 0.07\)			98
16 S	\(2.76\)	”			\(0.065\)	74 \( \mathrm{S}^{32}+n^1=\mathrm{Si}^{29}+\mathrm{He}^4 \)
16 S	\(2.50—2.38\)	”	\(2.38 \pm 0.10\)			37
16 S	\(0.860\)	RaTh \(\gamma\)—Be	\(2.5 \pm 0.4\)			81
16 S	\(0.83\)	\(\mathrm{Na}^{24}\gamma\)—Be	\(2.2\)			47
16 S	\(0.22\)	\(\mathrm{Na}^{24}\gamma\)—D\(_2\)O	\(2.9\)			47
16 S	\(0.210\)	RaTh \(\gamma\)—D	\(2.3 \pm 0.4\)			19
16 S	\(0.18\) or \(0.10\)	\(d\)—C	\(2.6\)	\(1.0 \pm 0.3\)	\(<0.35\)	44
16 S	\(0.15\)	RaC \(\gamma\)—Be				73
16 S	\(0.14\)	\(\mathrm{Mn}^{56}\gamma\)—Be	\(4.5\)			47
16 S	\(0.13\)	\(\mathrm{Ga}^{72}\gamma\)—D\(_2\)O	\(4.2\)			47
16 S	\(0.024\)	\(\mathrm{Sb}^{124}\gamma\)—Be	\(1.0\)			47
16 S	\(D\)	—		\(1.3 \pm 0.1\)		19
16 S	\(C\)	—		\(1.0\)		19
16 S	Slow	—	\(1.0\)			19
16 S	”	—	\(1.4\)			19
16 S	”	—	\(2.2\)			20
16 S	”	—		\(1.1\)		19
16 S	”	—		\(2.0\)		20
16 S	”	—			\(0.62\)	30
16 S	”	—			\(0.44 \pm 0.03\)	75 \(\sigma_{\mathrm{capture}}\)
16 S	”	—			\(0.35 \pm 0.03\)	70
17 Cl	—	\(d\)—Li	\(2.23 \pm 0.07\)			37 CCl\(_4\)
17 Cl	\(2.88 \pm 0.04\)	\(d\)—D	\(3.42 \pm 0.16\)			39 CCl\(_4\)

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
17 Cl	2.8–2.1	\(d\)—D	2.66…2.84 ± 0.10			\(^{28}\) CCl\(_4\)
17 Cl	2.50–2.38	″	2.78 ± 0.09			\(^{37}\) CCl\(_4\)
17 Cl	0.860	RaTh \(\gamma\)—Be	4.6 ± 1.6			\(^{31}\) PbCl\(_2\)
17 Cl	0.210	RaTh \(\gamma\)—D	3.8 ± 1.6			\(^{31}\) PbCl\(_2\)
17 Cl	0.18 or 0.10	\(d\)—C	2.7			\(^{44}\) NaCl
17 Cl	0.15	RaC \(\gamma\)—Be		3.5 ± 2.1	0.3	\(^{45}\)
17 Cl	C	—				\(^{63}\) Cl\(^{37}\)
17 Cl	Slow	—	52			\(^{19}\)
17 Cl	″	—	39			\(^{19}\)
17 Cl	″	—		<10		\(^{19}\)
17 Cl	″	—			24	\(^{20}\) NaCl
17 Cl	″	—			29 ± 2	\(^{47}\) NaCl
17 Cl	Thermal	—			27	\(^{19}\) HCl
18 Ar	2.5	\(d\)—D	2.51		\(\sim 10^{-4}\)	\(^{68}\) Ar\(^{40} + n^{1} =\) S\(^{37} +\) He\(^{4}\)
18 Ar	Thermal	—				\(^{19}\) \(\sim 300^\circ\) abs.
19 K	—	\(d\)—Li	3.10 ± 0.11			\(^{37}\)
19 K	2.88 ± 0.04	\(d\)—D	3.13 ± 0.15			\(^{39}\)
19 K	2.8–2.1	″	3.62…3.67 ± 0.18			\(^{28}\)
19 K	2.50–2.38	″	4.15 ± 0.17			\(^{37}\)
19 K	0.860	RaTh \(\gamma\)—Be	4.3 ± 1.0			\(^{31}\)
19 K	0.83	Na\(^{24}\) \(\gamma\)—Be	2.7			\(^{47}\)
19 K	0.62	La\(^{140}\) \(\gamma\)—Be	2.3			\(^{47}\)
19 K	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	1.7			\(^{47}\)

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
19 K	0.210	RaTh \(\gamma\)—D	\(7.4 \pm 1.4\)			\({}^{31}\)
19 K	0.18 or 0.10	\(d\)—C	\(3.8?\)			\({}^{44}\) KCl
19 K	0.14	Mn\(^{56}\) \(\gamma\)—Be	1.9			\({}^{47}\)
19 K	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	1.6			\({}^{47}\)
19 K	0.024	Sb\(^{124}\) \(\gamma\)—Be	1.2			\({}^{47}\)
19 K	C	—			\(\sim 1.5\)	\({}^{63}\) K\(^{41}\)
19 K	*	—			\(\sim 1.4\)	\({}^{69}\) K\(^{41}\)
19 K	Slow	—	8.2			\({}^{19}\) KF
19 K	*	—		1.5		\({}^{19}\) KF
19 K	*	—			2.0	\({}^{20}\) KHCO\(_3\)
19 K	Thermal	—			3.2	\({}^{19}\) KF
20 Ca	—	\(d\)—Li	\(3.65 \pm 0.17\)			\({}^{37}\) CaO
20 Ca	—	*	\(4.10 \pm 0.36\)			\({}^{37}\) CaCO\(_3\)
20 Ca	2.50—2.38	\(d\)—D	\(3.85 \pm 0.16\)			\({}^{37}\) CaO
20 Ca	0.860	RaTh \(\gamma\)—Be	\(5.2 \pm 0.9\)			\({}^{31}\)
20 Ca	0.210	RaTh \(\gamma\)—D	\(4.1 \pm 1.1\)			\({}^{31}\)
20 Ca	0.18 or 0.10	\(d\)—C	\(4.9?\)			\({}^{44}\) CaF\(_2\)
20 Ca	C	—			\(< 5\)	\({}^{63}\) Ca\(^{40}\)
20 Ca	Slow	—	11			\({}^{19}\)
20 Ca	*	—		9.5		\({}^{19}\)
20 Ca	*	—			0.23	\({}^{20}\) CaO
20 Ca	*	—			\(0.50 \pm 0.04\)	\({}^{75}\) \(\sigma_{\mathrm{capt}}\)
20 Ca	*	—			\(0.37 \pm 0.04\)	\({}^{70}\) CaF\(_2\)
21 Sc	Slow	—			\(\geqq 2.8\)	\({}^{20}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
22 Ti	—	\(d\)—Li	\(2.55 \pm 0.21\)			\(^{37}\) TiO\(_2\)
22 Ti	2.8—2.1	\(d\)—D	\(1.85 \ldots 2.11 \pm 0.28\)			\(^{28}\) TiO\(_2\)
22 Ti	2.50—2.38	"	\(1.73 \pm 0.16\)			\(^{37}\) TiO\(_2\)
22 Ti	0.18 and 0.10	\(d\)—C	4.4			\(^{44}\) TiO\(_2\)
22 Ti	C	—		6.2		\(^{19}\) TiO\(_2\)
22 Ti	Slow	—	11.9			\(^{19}\) TiO\(_2\)
22 Ti	"	—			3.8	\(^{20}\)
22 Ti	"	—			\(5.2 \pm 0.3\)	\(^{70}\) TiO\(_2\)
23 V	0.45 and 0.04	Ra \(\gamma\)—Be			\((2.1 \pm 0.2)\,10^{-3}\)	\(^{19}\)
23 V	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(9\,10^{-4}\)	\(^{19}\)
23 V	Slow	—	10			\(^{19}\)
23 V	"	—		\(< 4\)		\(^{19}\)
23 V	Thermal	—			6.8	\(^{19}\) VOSO\(_4\)
24 Cr	—	\(d\)—Li	\(3.05 \pm 0.08\)			\(^{37}\)
24 Cr	2.8—2.1	\(d\)—D	\(3.02 \ldots 3.21 \pm 0.09\)			\(^{28}\)
24 Cr	2.50—2.38	"	\(3.38 \pm 0.10\)			\(^{37}\)
24 Cr	0.860	RaTh \(\gamma\)—Be		\(3.9 \pm 0.6\)		\(^{76}\)
24 Cr	0.210	RaTh \(\gamma\)—D		\(6.1 \pm 0.8\)		\(^{76}\)
24 Cr	0.18 or 0.10	\(d\)—C	3.5			\(^{44}\)
24 Cr	0.09 and 0.5	Ra \(\gamma\)—Be		\(4.8 \pm 0.6\)		\(^{76}\) Cr\(_2\)O\(_3\)
24 Cr	1 eV	—		4		\(^{12}\)
24 Cr	Slow	—	4.9			\(^{19}\)
24 Cr	"	—		3.5		\(^{19}\)
24 Cr	"	—			\(2.5 \pm 0.05\)	\(^{70}\) Cr\(_2\)O\(_3\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
25 Mn	—	\(d\)—Li	\(3.18 \pm 0.08\)			87
25 Mn	\(2.88 \pm 0.04\)	\(d\)—D	\(3.82 \pm 0.82\)			39
25 Mn	\(2.8\text{–}2.1\)	"	\(3.08\ldots 3.31 \pm 0.10\)			28
25 Mn	\(2.50\text{–}2.38\)	"	\(3.02 \pm 0.07\)			87
25 Mn	\(0.860\)	RaTh \(\gamma\)—Be		\(4.3 \pm 0.7\)		38
25 Mn	\(0.45\) and \(0.04\)	Ra \(\gamma\)—Be			\((4.5 \pm 0.4)10^{-3}\)	19
25 Mn	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(9 \cdot 10^{-4}\)	19
25 Mn	\(0.210\)	RaTh \(\gamma\)—D		\(6.9 \pm 0.7\)		33
25 Mn	\(0.18\) and \(0.10\)	\(d\)—C	\(4.9\)			44 MnO\(_2\)
25 Mn	\(0.133\quad 0.530\)	Rn \(\gamma\)—Be		\(6.2 \pm 0.8\)		77
25 Mn	\(\sim 300\ \mathrm{eV}\)	—		\(5000\)		78 Res. scatt.
25 Mn	\(300 \pm 40\ \mathrm{eV}\)	—	\(>19\)	\(120\)		79
25 Mn	\(100\ \mathrm{eV}\)	—				80 Back scatt.
25 Mn	\(<30\ \mathrm{eV}\)	—	\(2.24 E_n^{-1/2} + 2.2\)			79
25 Mn	\(25\ \mathrm{eV}\)	—		\(6\)		80 Back scatt.
25 Mn	\(15\ \mathrm{eV}\)	—	\(\sim 3\)			79
25 Mn	\(D\)	—		\(8.4 \pm 0.7\)		19
25 Mn	\(1\ \mathrm{eV}\)	—		\(2.4\)		12
25 Mn	\(C\)	—		\(3.0\)		19
25 Mn	•	—	\(19.9\)			19 MnO
25 Mn	"	—	\(19.1\)			19 MnS
25 Mn	•	—	\(25.2\)			19 MnO\(_2\)
25 Mn	•	—	\(33.6\)			19 MnSO\(_4\)
25 Mn	Slow	—	\(14.3\)			19

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
25 Mn	Slow	—	15.1	2.1		\(^{19}\)
25 Mn	″	—			11.2	\(^{20}\)
25 Mn	″	—			\(10.7 \pm 0.2\)	\(^{20}\)
25 Mn	″	—			24.7	\(^{70}\) Mn and MnO\(_2\)
25 Mn	Therm.	—			\(\dfrac{24.7}{v}\)	\(^{81}\) \(v\) in km/sec
25 Mn	″	—			9.4	\(^{19}\)
26 Fe	—	\(d\)—Li	\(2.79 \pm 0.08\)			\(^{37}\)
26 Fe	3.1	\(d\)—D		\(0.81—0.54\)		\(^{59}\) Inverse elastic scattering
26 Fe	\(2.88 \pm 0.04\)	″	\(3.15 \pm 0.10\)			\(^{39}\)
26 Fe	\(2.8—2.1\)	″	\(2.55 \ldots 3.02 \pm 0.06\)			\(^{28}\)
26 Fe	—	″		\(0.655\ (23^\circ)\)		\(^{82}\)
26 Fe	—	″		\(0.588\ (33^\circ)\)		\(^{82}\)
26 Fe	—	″		\(0.339\ (44^\circ)\)		\(^{82}\)
26 Fe	—	″		\(0.175\ (55^\circ)\)		\(^{82}\)
26 Fe	—	″				\(^{82}\)
26 Fe	2.5	″	\(3.1 \pm 0.3\)			\(^{60}\)
26 Fe	2.5	″		\(4.3 \pm 0.3\ (45^\circ)\)		\(^{60}\)
26 Fe	2.5	″		\(2.0 \pm 0.4\ (100^\circ)\)		\(^{60}\)
26 Fe	2.5	″		\(1.7 \pm 0.3\ (45^\circ)\)		\(^{60}\) Elastic scattering
26 Fe	2.5	″		\(0.60 \pm 0.15\ (100^\circ)\)		\(^{60}\) Elastic scattering
26 Fe	2	″		1		\(^{6}\)
26 Fe	0.860	RaTh \(\gamma\)—Be		\(3.1 \pm 0.4\)		\(^{33}\)
26 Fe	0.83	Na\({}^{24}\gamma\)—Be	2.7			\(^{47}\)
26 Fe	0.22	Na\({}^{24}\gamma\)—D\(_2\)O	3.3			\(^{47}\)
26 Fe	0.210	RaTh \(\gamma\)—D		\(3.6 \pm 0.3\)		\(^{33}\)

Continuation

Element	$E_n$, MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scat}}$	$\sigma_{\mathrm{abs}}$	Note
26 Fe	0.18 or 0.10	$d$—C	3.7			44
	0.15	RaC $\gamma$—Be		$2.7 \pm 0.5$	0.13	108
	0.14	Mn56 $\gamma$—Be	3.9			47
	0.133 and 0.530	Rn $\gamma$—Be		$3.5 \pm 0.4$		77
	0.13	Ga72 $\gamma$—D$_2$O	4.1			47
	0.024	Sb124 $\gamma$—Be	2.2			47
	$D$	—		$9.0 \pm 0.5$		19
	1.44 eV	—		11.1		84
	1 eV	—		11.5		12
	$C$	—	39.2			19 Fe$_2$O$_3$
	”	—		13.06—11.39		85 Various Fe grains
	Slow	—	8.5		3.5	19
	•	—	13.6	10.3		19
	”	—	12.0			19
	”	—	12.8			20
	”	—		9.5		20
	”	—	$12.0 \mp 0.2$			19 Polycryst.
	”	—	$7.0$ and $6.1 \pm 1.0$			19 Monocryst.
	”	—			1.6	20 Fe$_2$O$_3$
	”	—			$2.1 \pm 0.2$	104
	•	—			2.1	20
	”	—			$2.05 \pm 0.15$	70 Fe$_2$O$_3$
	Thermal	—			$\leq 0.01$	61 Order of magnitude, $\sigma_{\mathrm{capt}}$
27 Co	—	$d$—Li	$3.23 \pm 0.16$			37 Co$_2$O$_3$
	2.50—2.38	$d$—D	$2.59 \pm 0.15$			87 Co$_2$O$_3$

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
27 C	0.860	RaTh \(\gamma\)—Fe		\(4.5 \pm 0.5\)		\(^{33}\)
27 C	0.210	RaTh \(\gamma\)—D		\(6.8 \pm 0.6\)		\(^{33}\)
27 C	0.18 or 0.10	\(d\)—C	\(5.2?\)			\(^{44}\)
27 C	0.133 and 0.530	Rn \(\gamma\)—Be		\(6.8 \pm 0.6\)		\(^{77}\)
27 C	\(115 \pm 5\) eV	—	\(>120\)			\(^{83}\) Resonance
27 C	\(< 5\) eV	—	\(0.4\,E_n^{-1/2}+6.7\)			\(^{59}\)
27 C	C	—		5		\(^{19}\)
27 C	Slow	—	39			\(^{19}\)
27 C	”	—	35			\(^{19}\)
27 C	”	—	26			\(^{20}\)
27 C	”	—		5		\(^{20}\)
27 C	”	—		5.6		\(^{20}\)
27 C	”	—			24.0	\(^{20}\) CoCO\(_3\)
27 C	Thermal	—			33	\(^{19}\) CoSO\(_4\)
28 Ni	—	\(d\)—Li	\(2.92 \pm 0.08\)			\(^{37}\)
28 Ni	2.8–2.1	\(d\)—D	\(2.48\ldots 2.78 \pm 0.08\)			\(^{28}\)
28 Ni	2.50–2.38	”	\(2.56 \pm 0.08\)			\(^{37}\)
28 Ni	0.860	RaTh \(\gamma\)—Be		\(3.4 \pm 0.7\)		\(^{33}\)
28 Ni	0.83	Na\({}^{24}\) \(\gamma\)—Be	3.5			\(^{47}\)
28 Ni	0.62	La\({}^{140}\) \(\gamma\)—Be	3.7			\(^{47}\)
28 Ni	0.22	Na\({}^{24}\) \(\gamma\)—D\(_2\)O	5.8			\(^{47}\)
28 Ni	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(<9 \cdot 10^{-1}\)	\(^{19}\)
28 Ni	0.210	RaTh \(\gamma\)—D		\(5.7 \pm 0.6\)		\(^{33}\)
28 Ni	0.18 or 0.10	\(d\)—C	6.6			\(^{44}\) NiO
28 Ni	0.14	Mn\({}^{56}\) \(\gamma\)—Be	4.2			\(^{47}\)

Continuation,

Element	\(E_n\) in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
28 Ni	0.133 and 0.530	Rn \(\gamma\)—Be		\(6.0 \pm 0.8\)		77
28 Ni	0.13	\(Ga^{72}\gamma\)—\(D_2O\)	6.4			47
28 Ni	0.024	\(Sb^{124}\gamma\)—Be	23			47
28 Ni	\(D\)	—		\(19 \pm 1\)		19
28 Ni	1 eV	—		18		12
28 Ni	\(C\)	—		16.8		19
28 Ni	”	—	22.3			19 NiO
28 Ni	”	—			(0.8)	63 \((Ni^{62})\)
28 Ni	Slow	—	19.7			19
28 Ni	·	—	15.4			19
28 Ni	·	—	21.2			20
28 Ni	·	—		12.4		19
28 Ni	·	—		13.9		20
28 Ni	·	—	20.0			19
28 Ni	”	—	\(19.8 \pm 0.5\)			19
28 Ni	”	—	\(14.1 \pm 1.2\)			19
28 Ni	”	—			3.6	20
28 Ni	”	—			\(6.2 \pm 0.5\)	75
28 Ni	”	—			\(5.6 \pm 0.5\)	70 \(Ni_2O_3\)
29 Cu	—	\(d\)—Li	\(2.97 \pm 0.05\)			87
29 Cu	\(2.88 \pm 0.04\)	\(d\)—D	\(2.82 \pm 0.10\)			89
29 Cu	2.8—2.1	”	\(2.50 \ldots 2.71 \pm 0.06\)			88
29 Cu	2.50—2.38	”	\(2.59 \pm 0.06\)			37
29 Cu	2.5	”	\(2.7 \pm 0.3\)			60
29 Cu	2.5	”		\(3.5 \pm 0.3\) (45°)		60

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
29 Cu	2.5	\(d—D\)		\(2.2 \pm 0.2\) \((100^\circ)\)		^60
29 Cu	2.5	”		\(1.4 \pm 0.3\) \((45^\circ)\)		^60 Elast. scatt.
29 Cu	2.5	”		\(0.36 \pm 0.1\) \((100^\circ)\)		^60 Elast. scatt.
29 Cu	2.5	”		\(0.448\) \((23^\circ)\)		^82
29 Cu	2.5	”		\(0.418\) \((33^\circ)\)		^82
29 Cu	2.5	”		\(0.276\) \((44^\circ)\)		^82
29 Cu	2.5	”		\(0.186\) \((55^\circ)\)		^82
29 Cu	0.860	RaTh \(\gamma—\mathrm{Be}\)	\(2.78 \pm 0.15\)			^29
29 Cu	0.860	”		\(2.5 \pm 0.4\)		^43
29 Cu	0.83	Na\(^ {24}\gamma—\mathrm{Be}\)	3.8			^47
29 Cu	0.45 and 0.04	Ra \(\gamma—\mathrm{Be}\)			\((3.5 \pm 0.8)10^{-3}\)	^19 Cu\(^ {64}\)
29 Cu	0.45 and 0.04	”			\((2.1 \pm 0.2)10^{-3}\)	^19 Cu\(^ {66}\)
29 Cu	0.22	Na\(^ {24}\gamma—\mathrm{D_2O}\)	5.3			^47
29 Cu	\(0.22 \pm 0.04\)	ThC″ \(\gamma—D\)			\(9 \cdot 10^{-4}\)	^19
29 Cu	0.210	RaTh \(\gamma—D\)		\(4.8 \pm 1.0\)		^33
29 Cu	0.18 or 0.10	\(d—C\)	3.6			^44
29 Cu	0.15	RaC \(\gamma—\mathrm{Be}\)		\(4.2 \pm 0.7\)	\(< 0.18\)	^60
29 Cu	0.14	Mn\(^ {56}\gamma—\mathrm{Be}\)	5.9			^47
29 Cu	0.13	Ga\(^ {72}\gamma—\mathrm{D_2O}\)	6.2			^47
29 Cu	0.024	Sb\(^ {124}\gamma—\mathrm{Be}\)	8.0			^47
29 Cu	1.44 eV	—		8.3		^84
29 Cu	\(D\)	—		\(8.0 \pm 0.8\)		^19
29 Cu	1 eV	—		8		^12
29 Cu	\(1\ \mathrm{eV} > E_n > 0.5\ \mathrm{eV}\)	—	7.88			^19
29 Cu	\(C\)	—		\(10.84–7.04\)		^85 Separate Cu grains
29 Cu	”	—			2.4	^68 Cu\(^ {65}\)
29 Cu	”	—			1.8	^69 Cu\(^ {65}\)
29 Cu	Slow	—	11.9			^19

Continuation

Element	\(P_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\text{scatt}}\)	\(\sigma_{\text{abs}}\)	Note
29 Cu	Slow	—	7.5			19
29 Cu	"	—	10.3			20
29 Cu	"	—		8.6		19
29 Cu	"	—		5.5		20
29 Cu	"	—	10.5			19
29 Cu	"	—			2.2 (2.6)	20
29 Cu	"	—			3.6	20
29 Cu	"	—			\(4.3 \pm 0.3\)	75
29 Cu	"	—			\(3.4 \pm 0.3\)	70 CuO
30 Zn	—	\(d\)—Li	\(2.80 \pm 0.07\)			37
30 Zn	\(2.88 \pm 0.04\)	\(d\)—D	\(3.28 \pm 0.10\)			38
30 Zn	2.8—2.1	"	\(2.62 \ldots 2.74 \pm 0.09\)			38
30 Zn	2.5	"	\(3.0 \pm 0.3\)			60
30 Zn	2.5	"		\(1.7 \pm 0.3\) (45°)		60 Elastic scatt.
30 Zn	2.5	"		\(0.68 \pm 0.2\) (100°)		60 Elastic scatt.
30 Zn	2.50—2.38	"	\(2.68 \pm 0.09\)			37
30 Zn	0.860	RaTh \(\gamma\)—Be		\(2.8 \pm 0.3\)		83
30 Zn	0.83	Na\(^{24}\) \(\gamma\)—Be	4.3			47
30 Zn	0.62	La\(^{140}\) \(\gamma\)—Be	4.7			47
30 Zn	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	5.1			47 *
30 Zn	0.210	Ra h \(\gamma\)—D		\(4.0 \pm 0.4\)		53
30 Zn	0.18 or 0.10	\(d\)—C	3.6			44
30 Zn	0.15	RaC \(\gamma\)—Be		\(4.0 \pm 0.7\)	\(< 0.16\)	73
30 Zn	0.14	Mn\(^{56}\) \(\gamma\)—Be	5.4			47
30 Zn	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	6.6			47

Continuation

Element	\(E_n\) in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
30 Zn	0.024	Sb\(^{124}\)\(\gamma\)—Be	9.9			\(^{47}\)
30 Zn	1.44 eV	—		4.2		\(^{84}\)
30 Zn	\(D\)	—		\(8.2 \pm 0.2\)		\(^{19}\)
30 Zn	1.00 eV	—		4.2		\(^{12}\)
30 Zn	\(C\)	—		5.5		\(^{19}\)
30 Zn	Slow	—	4.7			\(^{19}\)
30 Zn	”	—	4.5			\(^{19}\)
30 Zn	”	—		5.2	1.2	\(^{90}\)
30 Zn	”	—			\(1.0 \pm 0.06\)	\(^{75}\)
30 Zn	”	—			\(0.92 \pm 0.06\)	\(^{70}\)
31 Ga	\(C\)	—			1	\(^{68}\) Ga\(^{69}\)
31 Ga	”	—			2.6	\(^{100}\) Ga\(^{71}\)
31 Ga	Slow	—	\(18.5 \pm 7.6\)			\(^{86}\)
31 Ga	”	—		\(< 4\)		\(^{19}\)
32 Ge	95 eV	—	\(>14\)			\(^{83}\) Resonance
32 Ge	40–2.2 eV	—	8.3			\(^{83}\)
32 Ge	1 eV	—		22		\(^{12}\)
32 Ge	Slow	—	\(21.3 \pm 7.3\)			\(^{86}\)
32 Ge	”	—	\(\sim 75\)			\(^{19}\) Calculated

Continuation

Element	\(E_n\) in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Notes
33 As	—	\(d\)—Li	\(3.83 \pm 0.09\)			\(^{37}\)
33 As	2.50—2.38	\(d\)—D	\(3.39 \pm 0.13\)			\(^{37}\)
33 As	0.860	RaTh \(\gamma\)—Be		\(5.8 \pm 0.7\)		\(^{38}\)
33 As	0.45 and 0.04	Ra \(\gamma\)—Be			\((3.2 \pm 0.2)\,10^{-2}\)	\(^{19}\) As\(^{76}\)
33 As	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(8.3 \cdot 10^{-3}\)	\(^{19}\) As\(^{75}\)
33 As	0.210	RaTh \(\gamma\)—D		\(6.3 \pm 0.5\)		\(^{38}\)
33 As	0.18 or 0.10	\(d\)—C	4.7			\(^{44}\)
33 As	0.133 and 0.530	Rn \(\gamma\)—Be		\(7.1 \pm 1.1\)		\(^{77}\)
33 As	\(D\)	—		\(6.1 \pm 0.8\)		\(^{19}\)
33 As	Slow	—	8.6			\(^{19}\)
33 As	"	—		7.1		\(^{19}\)
33 As	"	—			3.5	\(^{20}\)
33 As	"	—			5.2	\(^{20}\)
33 As	Thermal	—			6.5	\(^{20}\)
34 Se	\(2.88 \pm 0.04\)	\(d\)—D	\(4.05 \pm 0.16\)			\(^{39}\)
34 Se	0.860	RaTh \(\gamma\)—Be		\(4.8 \pm 0.8\)		\(^{38}\)
34 Se	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(< 3 \cdot 10^{-4}\)	\(^{19}\)
34 Se	0.210	RaTh \(\gamma\)—D		\(5.5 \pm 0.5\)		\(^{37}\)
34 Se	0.18 or 0.10	\(d\)—C	4.5			\(^{44}\)
34 Se	0.133 and 0.530	Rn \(\gamma\)—Be		\(5.8 \pm 0.7\)		\(^{77}\)
34 Se	\(D\)	—		\(12.0 \pm 0.7\)		\(^{19}\)
34 Se	\(C\)	—		10		\(^{12}\)
34 Se	Slow	—	20.4	12.7		\(^{19}\)
34 Se	"	—	19			\(^{19}\)
34 Se	"	—			12.0	\(^{20}\)
34 Se	Thermal	—			11.5	\(^{19}\) H\(_2\)SeO\(_3\)
34 Se	"	—			0.2	\(^{88}\) Se\(^{74} + n^1 =\) Se\(^{75} + \gamma\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
35 Br	—	\(d-\mathrm{Li}\)	\(3.21 \pm 0.23\)			37 KBr
35 Br	\(2.50–2.38\)	\(d-\mathrm{D}\)	\(2.69 \pm 0.33\)			37 KBr
35 Br	\(0.860\)	\(\mathrm{RaTh}\,\gamma-\mathrm{Be}\)		\(7.3 \pm 1.0\)		38
35 Br	\(0.45\) and \(0.04\)	\(\mathrm{Ra}\,\gamma-\mathrm{Be}\)			\((7.6 \pm 0.4)\,10^{-2}\)	19 Br80
35 Br	\(0.22 \pm 0.01\)	\(\mathrm{ThC}^{\prime\prime}\,\gamma-\mathrm{D}\)			\(1.60\,10^{-2}\)	19 Br79
35 Br	\(0.22 \pm 0.04\)	same			\(3.01\,10^{-3}\)	19 Br81
35 Br	\(0.210\)	\(\mathrm{RaTh}\,\gamma-\mathrm{D}\)		\(7.8 \pm 0.8\)		87
35 Br	\(0.18\) or \(0.10\)	\(d-\mathrm{C}\)	\(6.6\)			44 NaBr
35 Br	C	—	\(7.3\)			19
35 Br	—	—		\(7\)		12
35 Br	Slow	—	\(11.8\)			19
35 Br	same	—		\(< 7\)		19
35 Br	same	—			\(3.2\)	20
35 Br	same	—	\(740\)			19 Resonance
35 Br	Thermal	—			\(7\)	19 NaBr
36 Kr	\(2.5\)	\(d-\mathrm{D}\)			\(\leq 3 \cdot 10^{-6}\)	68
36 Kr	Slow	—	\(23.5 \pm 14\)			89
37 Rb	Slow	—	\(11.8 \pm 1.9\)			80 RbI
38 Sr	—	\(d-\mathrm{Li}\)	\(5.22 \pm 0.21\)			87 SrO
38 Sr	—	same	\(4.30 \pm 0.37\)			37 SrCO\(_3\)
38 Sr	\(2.50–2.38\)	\(d-\mathrm{D}\)	\(4.14 \pm 0.21\)			37 SrO
38 Sr	\(0.18\) or \(0.10\)	\(d-\mathrm{C}\)	\(5.8\)			44 SrO

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
38 Sr	C	—	\(\sim 9\)	10		\(^{12}\)
38 Sr	Slow	—				\(^{19}\)
38 Sr	"	—		9.5	1.5	\(^{19}\) SrS
38 Sr	"	—			\(1.3 \pm 0.1\)	\(^{20}\) SrO
38 Sr	"	—			0.13	\(^{70}\) SrCO\(_3\), capture
38 Sr	Thermal	—				\(^{90}\) Sr\(^{86} + n^1 =\) Sr\(^{87} + \gamma\)
39 Y	0.45 and 0.04	Ray—Be		\(< 14\)	\((1.9 \pm 0.2)10^{-3}\)	\(^{19}\) Y\(^{90}\)
39 Y	Slow	—				\(^{19}\) Y\(_2\)O\(_3\)
39 Y	Thermal	—	4			\(^{91}\)
40 Zr	7.6 eV	—	\(>20\)			\(^{92}\) Resonance
40 Zr	2.3 eV	—	\(>25\)			\(^{92}\)
40 Zr	1.09 eV	—	\(>25\)			\(^{92}\)
40 Zr	\(<0.6\) eV	—	\(0.74\,E_n^{-1/2} + 6,\!?\)			\(^{92}\)
40 Zr	"	—	\(16.7\)			\(^{19}\)
40 Zr	Slow	—		16		\(^{19}\)
40 Zr	"	—				\(^{19}\)
40 Zr	"	—			0.35	\(^{20}\) Zr(OH)\(_4\)
41 Nb	5000—0.5 eV	—	6.2			\(^{83}\)
41 Nb	1—0.05 eV	—	\(0.10\,E_n^{-1/2} + 6.4\)			\(^{83}\)
41 Nb	C	—	\(\sim 14\)	5		\(^{12}\)
41 Nb	Slow	—				\(^{19}\)
41 Nb	"	—		5		\(^{19}\)
41 Nb	"	—			1.5	\(^{20}\)
41 Nb	Thermal	—			1.44	\(^{50}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
42 Mo	\(2.88 \pm 0.04\)	\(d{-}D\)	\(1.06 \pm 0.11\)			89
42 Mo	0.860	RaTh \(\gamma{-}\)Be		\(7.9 \pm 1.4\)		35
42 Mo	0.210	RaTh \(\gamma{-}D\)		\(9.6 \pm 1.2\)		35
42 Mo	0.133 and 0.530	Rn \(\gamma{-}\)Be		\(9.8 \pm 1.0\)		77
42 Mo	C	—		6.5		12
42 Mo	Slow	—	7.1			19
42 Mo	”	—		6.7		19
42 Mo	”	—			5.8	80
42 Mo	”	—			\(2.3 \pm 0.05\)	70 MoO\(_3\)
44 Ru	C	—		6		12
44 Ru	Slow	—	12.5			19
44 Ru	”	—		5.9		19
45 Rh	1.30 eV	—			\(>2500\)	93 Resonance
45 Rh	1.28 eV	—	\(>1500\)			94 ”
45 Rh	\(\sim 0.9\) eV	—			6100	19 ”
45 Rh	D	—	115			19
45 Rh	C	—	102			19
45 Rh	Slow	—	170			19
45 Rh	”	—			149	20
46 Pd	\(0.22 \pm 0.01\)	ThC″ \(\gamma{-}D\)			\(2.5 \cdot 10^{-2}\)	19 Pd\(^{108}\)
46 Pd	C	—		4.5		12
46 Pd	Slow	—	10			19
46 Pd	”	—		3		19

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
47 Ag	—	\(d-\mathrm{Li}\)	\(3.56\pm0.12\)			37
47 Ag	\(2.8—2.1\)	\(d-\mathrm{D}\)	\(3.57\ldots3.81\pm0.15\)			38
47 Ag	2.5	"			0.7	19
47 Ag	\(2.50—2.33\)	"	\(4.30\pm0.17\)			37
47 Ag	0.860	\(\mathrm{RaTh}\,\gamma-\mathrm{Be}\)		\(6.6\pm0.7\)		76
47 Ag	0.83	\(\mathrm{Na}^{24}\gamma-\mathrm{Be}\)	7.2			47
47 Ag	0.62	\(\mathrm{La}^{140}\gamma-\mathrm{Be}\)	7.3			47
47 Ag	0.45 and 0.04	\(\mathrm{Ra}\,\gamma-\mathrm{Be}\)			\(0.1\pm0.06\)	19 \(\mathrm{Ag}^{108}\)
47 Ag	0.22	\(\mathrm{Na}^{24}\gamma-\mathrm{D_2O}\)	7.8			47
47 Ag	\(0.22\pm0.04\)	\(\mathrm{ThC}^{\prime\prime}\gamma-\mathrm{D}\)			0.03	19 \(\mathrm{Ag}^{107}\)
47 Ag	\(0.22\pm0.04\)	"			0.046	19 \(\mathrm{Ag}^{109}\)
47 Ag	0.210	\(\mathrm{RaTh}^{\prime\prime}\gamma-\mathrm{D}\)		\(8.1\pm0.7\)		76
47 Ag	0.18 or 0.10	\(d-\mathrm{C}\)	5.5			44
47 Ag	0.14	\(\mathrm{Mn}^{56}\gamma-\mathrm{Be}\)	8.1			47
47 Ag	0.13	\(\mathrm{Ga}^{72}\gamma-\mathrm{D_2O}\)	8.1			47
47 Ag	0.09 and 0.5	\(\mathrm{Ra}\,\gamma-\mathrm{Be}\)		\(5.6\pm0.8\)		106
47 Ag	0.024	\(\mathrm{Sb}^{124}\gamma-\mathrm{Be}\)	8.0			47
47 Ag	\(1000—80\ \mathrm{eV}\)	—	\(8—9\)			79
47 Ag	\(45\pm4\ \mathrm{eV}\)	—	\(>16\)			79 Resonance
47 Ag	\(43\pm5\ \mathrm{eV}\)	—	\(>14\)			46 "
47 Ag	\(16\pm1\ \mathrm{eV}\)	—	\(>20\)			79 "
47 Ag	\(13.7\pm1\ \mathrm{eV}\)	—	\(>14\)			46 "
47 Ag	\(5.1\ \mathrm{eV}\)	—	\(>900\)			79 "
47 Ag	\(5.1\pm0.2\ \mathrm{eV}\)	—	\(>100\)			46 "
47 Ag	\(D\)	—		\(9.1\pm0.8\)		19
47 Ag	\(0.5—0\ \mathrm{eV}\)	—		6.6		12
47 Ag	\(\sim0.5—0.015\ \mathrm{eV}\)	—	\(9.05\,E_n^{-1/2}+6.6\)			45

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
47 Ag	C	—	535	\(\sim 1\)		19
47 Ag	Slow	—	97			19
47 Ag	"	—	63			19
47 Ag	"	—	55			19
47 Ag	"	—			58	20
47 Ag	"	—	3560			19 Resonance
47 Ag	"	—		6,3		20
47 Ag	"	—			64	20
47 Ag	"	—			\(0,19 \pm 0,02\)	95 Capture
48 Cd	—	\(d\)—Li	\(3,71 \pm 0,15\)			37
48 Cd	2,8—2,1	\(d\)—D	\(3,75 \ldots 4,14 \pm 0,15\)			28
48 Cd	2,50—2,38	"	\(4,07 \pm 0,17\)			37
48 Cd	0,860	RaTh \(\gamma\)—Be		\(7,4 \pm 0,9\)		76
48 Cd	0,83	Na24 \(\gamma\)—Be	7,1			47
48 Cd	0,22	Na24 \(\gamma\)—D\(_2\)O	7,3			47
48 Cd	0,210	RaTh \(\gamma\)—D		\(9,6 \pm 1,1\)		76
48 Cd	0,18 or 0,10	\(d\)—C	4,9			44
48 Cd	0,14	Mn56 \(\gamma\)—Be	7,3			47
48 Cd	0,13	Ga72 \(\gamma\)—D\(_2\)O	7,6			47
48 Cd	0,09 and 0,5	Ra \(\gamma\)—Be		\(5,7 \pm 0,8\)		76
48 Cd	0,024	Sb124 \(\gamma\)—Be	6,9			47
48 Cd	1 eV	—		5,3		12
48 Cd	0,18 eV	—	\(7800 \pm 800\)			55 Resonance
48 Cd	0,180 eV	—	7800	6,0		96 "

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
48 Cd	0.178 eV	—	7250	5.30±0.7		\(^{97}\) Resonance
48 Cd	0.176 eV	—	7200±200			\(^{73}\)
48 Cd	0.04 eV	—	2300±650			\(^{55}\)
48 Cd	\(D\)	—		3.7±0.4		\(^{19}\)
48 Cd	Slow	—	4500			\(^{19}\)
48 Cd	"	—	3300			\(^{19}\)
48 Cd	"	—	2640			\(^{19}\)
48 Cd	"	—		1.2		\(^{20}\)
48 Cd	"	—			2950	\(^{20}\) Cd \((\mathrm{NO}_3)_2\)
48 Cd	"	—			0.1	\(^{98}\) Sample Cd\(^{117}\)
48 Cd	"	—			0.3	\(^{98}\) Sample Cd\(^{115}\) (2.5 days)
48 Cd	"	—			0.04	\(^{98}\) Sample Cd\(^{115}\) (43 days)
48 Cd	Thermal	—			2900	\(^{19}\) Cd\((\mathrm{NO}_3)_2\), resonance
49 In	0.45 and 0.04	Ra \(\gamma\)—Be			\((4.7±0.4)\,10^{-2}\)	\(^{19}\) In\(^{116}\)
49 In	8.6±0.4 eV	—	\(>3000\)			\(^{93}\) Resonance
49 In	3.8±0.2 eV	—	\(>1200\)			\(^{98}\) "
49 In	1.44±0.02 eV	—	\(>26000\)	764–626		\(^{93}\) "
49 In	1.44 eV	—				\(^{93}\) "
49 In	1.44±0.01 eV	—	\(>5200\)			\(^{99}\) "
49 In	1.39 eV	—	\(>15000\)			\(^{46}\) "
49 In	Slow	—			\(>20000\)	\(^{93}\) "
49 In	"	—			147	\(^{19}\) "
49 In	"	—	198±11.3			\(^{20}\) "
49 In	"	—				\(^{86}\)
49 In	"	—			2.52	\(^{98}\) In+\(n\)=In(48 days)+\(\gamma\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
50 Sn	\(2.88 \pm 0.04\)	\(d\)—Li	\(3.60 \pm 0.13\)			37
50 Sn	\(2.8—2.1\)	\(d\)—D	\(4.39 \pm 0.16\)			39
50 Sn	\(2.50—2.38\)	”	\(3.82\ldots 4.15 \pm 0.14\)			28
50 Sn	—	”	\(3.82 \pm 0.19\)			37
50 Sn	—	”		\(0.760\ (23^\circ)\)		82
50 Sn	—	”		\(0.758\ (33^\circ)\)		88
50 Sn	—	”		\(0.382\ (44^\circ)\)		88
50 Sn	—	”		\(0.335\ (55^\circ)\)		88
50 Sn	\(0.860\)	RaTh \(\gamma\)—Be		\(4.9 \pm 0.5\)		33
50 Sn	\(0.83\)	Na\(^{24}\) \(\gamma\)—Be	\(6.7\)			47
50 Sn	\(0.62\)	La\(^{140}\) \(\gamma\)—Be	\(6.8\)			47
50 Sn	\(0.22\)	Na\(^{24}\) \(\gamma\)—D\(_2\)O	\(6.3\)			47
50 Sn	\(0.210\)	RaTh \(\gamma\)—D		\(4.9 \pm 0.6\)		30
50 Sn	\(0.18\) or \(0.10\)	\(d\)—C	\(5.2\)			44
50 Sn	\(0.15\)	RaC \(\gamma\)—Be		\(5.2 \pm 1.1\)	\(<0.30\)	73
50 Sn	\(0.14\)	Mn\(^{56}\) \(\gamma\)—Be	\(6.4\)			47
50 Sn	\(0.133\) and \(0.530\)	Rn \(\gamma\)—Be		\(4.1 \pm 0.6\)		77
50 Sn	\(0.13\)	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	\(6.4\)			42
50 Sn	\(0.024\)	Sb\(^{124}\) \(\gamma\)—Be	\(5.9\)			47
50 Sn	\(D\)	—		\(4.9 \pm 1.3\)		30
50 Sn	\(1\) eV	—		\(5.0\)		12
50 Sn	Slow	—	\(4.0\)			18
50 Sn	”	—		\(4.9\)		19
50 Sn	”	—			\(0.40\)	20
50 Sn	”	—			\(0.53 \pm 0.05\)	70
51 Sb	—	\(d\)—Li	\(4.36 \pm 0.13\)			37
51 Sb	\(2.8—2.1\)	\(d\)—D	\(4.50\ldots 4.80 \pm 0.14\)			28
51 Sb	\(2.50—2.38\)	”	\(4.88 \pm 0.16\)			37

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
51 Sb	0,860	RaTh \(\gamma\)—Be		\(4,3\pm0,6\)		\(^{88}\)
51 Sb	0,83	Na\(^{24}\)\(\gamma\)—Be	6,4			\(^{47}\)
51 Sb	0,62	La\(^{140}\)\(\gamma\)—Be	5,7			\(^{47}\)
51 Sb	0,45 and 0,04	Ra \(\gamma\)—Be			\((6,3\pm0,6)\,10^{-2}\)	\(^{19}\) Sb\(^{122,124}\)
51 Sb	0,22	Na\(^{24}\)\(\gamma\)—D\(_2\)O	6,1			\(^{47}\)
51 Sb	\(0,22\pm0,04\)	ThC\(^{\prime\prime}\)\(\gamma\)—D			0,011	\(^{19}\) Sb\(^{121}\)
51 Sb	0,210	RaTh \(\gamma\)—D		\(5,8\pm0,7\)		\(^{88}\)
51 Sb	0,18 or 0,10	\(d\)—C	5,4			\(^{44}\)
51 Sb	0,14	Mn\(^{56}\)\(\gamma\)—Be	6,4			\(^{47}\)
51 Sb	0,133 and 0,530	Rn \(\gamma\)—Be		\(4,4\pm0,6\)		\(^{77}\)
51 Sb	0,13	Ga\(^{72}\)\(\gamma\)—D\(_2\)O	6,9			\(^{47}\)
51 Sb	0,024	Sb\(^{124}\)\(\gamma\)—Be	6,3			\(^{47}\)
51 Sb	\(\sim1000\)—40 eV	—	6			\(^{79}\)
51 Sb	\(21\pm1,5\) eV	—	\(>19\)			\(^{79}\) Resonance
51 Sb	\(19,2\pm1,0\) eV	—	\(>12,5\)			\(^{46}\)
51 Sb	\(15\pm1\) eV	—	\(>22\)			\(^{79}\)
51 Sb	\(6,3\pm0,2\) eV	—	\(>15\)			\(^{46}\)
51 Sb	\(5,8\pm0,15\) eV	—	\(>40\)			\(^{79}\)
51 Sb	\(D\)	—		\(3,0\pm1,0\)		\(^{19}\)
51 Sb	1 eV	—		4,2		\(^{18}\)
51 Sb	1—0,015 eV	—	\(0,64\,E_n^{-1/2}+4,2\)			\(^{46,79}\)
51 Sb	\(C\)	—		1,7		\(^{19}\)
51 Sb	•	—			3,6	\(^{88}\) Sb\(^{121}\)
51 Sb	•	—			3,3	\(^{80}\) ”
51 Sb	”	—			2,3	\(^{63}\) Sb\(^{123}\)
51 Sb	Slow	—	8,1			\(^{19}\)
51 Sb	•	—		6,5		\(^{19}\)
51 Sb	•	—			4,4	\(^{20}\) Sb\(_2\)O\(_3\)
51 Sb	•	—			\(5,3\pm0,3\)	\(^{75}\)
51 Sb	”	—			\(4,8\pm0,3\)	\(^{70}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
52 Te	0.860	RaTh \(\gamma\)—Be		\(5.3 \pm 0.6\)		\(^{33}\)
52 Te	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(>0.001\)	\(^{19}\)
52 Te	0.210	RaTh \(\gamma\)—D		\(5.7 \pm 0.9\)		\(^{33}\)
52 Te	0.133 and 0.530	Rn \(\gamma\)—Be		\(5.1 \pm 0.7\)		\(^{77}\)
52 Te	C	—		5.3		\(^{20}\)
52 Te	Slow	—	8.2			\(^{19}\)
52 Te	″	—			2.95	\(^{20}\)
53 I	—	\(d\)—Li	\(4.36 \pm 0.19\)			\(^{37}\)
53 I	2.8—2.1	\(d\)—D	\(4.75 \ldots 4.95 \pm 0.20\)			\(^{88}\)
53 I	2.50—2.38	″	\(5.40 \pm 0.25\)			\(^{37}\)
53 I	0.860	RaTh \(\gamma\)—Be		\(7.8 \pm 0.9\)		\(^{33}\)
53 I	0.83	Na\(^{24}\) \(\gamma\)—Be	6.7			\(^{47}\)
53 I	0.62	La\(^{140}\) \(\gamma\)—Be	6.8			\(^{47}\)
53 I	0.45 and 0.04	Ra \(\gamma\)—Be			\((6.9 \pm 0.4)\,10^{-2}\)	\(^{19}\) J\(^{128}\)
53 I	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	6.1			\(^{47}\)
53 I	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D			\(1.75 \cdot 10^{-2}\)	\(^{19}\) J\(^{127}\)
53 I	0.210	RaTh \(\gamma\)—D		\(4.7 \pm 0.8\)		\(^{33}\)
53 I	0.18 or 0.10	\(d\)—C	6.6			\(^{44}\) KJ
53 I	0.14	Mn\(^{56}\) \(\gamma\)—Be	6.5			\(^{47}\)
53 I	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	6.6			\(^{47}\)
53 I	0.024	Sb\(^{124}\) \(\gamma\)—Be	7.0			\(^{47}\)
53 I	200,000—50 eV	—	\(\sim 6\)			\(^{88}\)
53 I	500 eV	—	\(\sim 7\)			\(^{100}\)
53 I	42—32 eV	—	\(>16\)			\(^{89}\) Resonance
53 I	38 eV	—	\(>40\)			\(^{100}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
53 J	\(20,6\pm0,4\ \mathrm{eV}\)	—	\(>7,5\)			\(^{49}\) Resonance
53 J	\(20,3\ \mathrm{eV}\)	—	\(\ge 20,5\)			\(^{100}\)
53 J	\(\sim 15{-}0,005\ \mathrm{eV}\)	—	\(1,66\,E_n^{-1/2}+3,6\)			\(^{100}\)
53 J	\(1{-}0,04\ \mathrm{eV}\)	←	\(1,12\,E_n^{-1/2}+3,8\)	\(<4,8\)		\(^{88}\)
53 J	D	—		\(4,1\)		\(^{10}\)
53 J	C	—				\(^{19}\)
53 J	Slowed down	—	\(9,4\)		\(5,0\)	\(^{19}\)
53 J	"	—				\(^{20}\ \mathrm{PbJ}_2\)
53 J	"	—	\(14\)		\(6,25\)	\(^{20}\)
53 J	"	—			\(\sim 8\)	\(^{101}\ \mathrm{J}^{127}\), capture
53 J	"	—			\(6,8\)	\(^{101}\ \mathrm{J}^{129}\), "
53 J	Thermal	—	\(10,3\)			\(^{19}\ \mathrm{NaJ}\)
53 J	.	—				\(^{100}\ 300^\circ\) abs.
54 X	Slowed down	—	\(36,9\pm13\)			\(^{89}\)
55 Cs	Slowed down	—	\(50,5\pm3,8\)			\(^{86}\ \mathrm{CsCl}\)
56 Ba	—	\(d-\mathrm{Li}\)	\(6,15\pm0,22\)			\(^{37}\ \mathrm{BaO}\)
56 Ba	—	"	\(5,80\pm0,37\)			\(^{37}\ \mathrm{BaCO}_3\)
56 Ba	\(2,8{-}2,1\)	\(d-\mathrm{D}\)	\(6,51\ldots6,89\pm0,27\)			\(^{28}\ \mathrm{BaO}\)
56 Ba	\(2,50{-}2,38\)	"	\(6,19\pm0,23\)			\(^{37}\) "

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
56 Ba	0.860 0.22 ± 0.04 0.210 0.09 and 0.5 C Slow 〃 〃 Therm.	RaTh \(\gamma\)—Be ThC″ \(\gamma\)—D RaTh \(\gamma\)—D Ra \(\gamma\)—Be — — — — —	10	5.1 ± 0.8 7.1 ± 0.8 8.1 ± 1.0 8.2	\(<2\cdot10^{-4}\) 0.95 1.3 ± 0.1 \< 1	\(^{76}\) \(^{19}\) Ba\(^{138}\) \(^{75}\) \(^{76}\) \(^{19}\) BaF\(_2\) \(^{20}\) BaCO\(_3\) \(^{20}\) \(^{70}\) BaO \(^{19}\) Ba \((\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2\)
57 La	0.45 and 0.04 C 〃 Slow 〃 〃 Therm.	Ra \(\gamma\)—Be — — — — — —	26 ± 7 32 ± 7 80 10 10		\((4 \pm 0.5)\,10^{-3}\) 9.1	\(^{19}\) La\(^{140}\) \(^{19}\) \(^{19}\) \(^{19}\) \(^{19}\) \(^{80}\) La \((\mathrm{CH}_3\mathrm{COO})_3\) \(^{21}\)
58 Ce	Э Slow 〃	— — —	3 ± 4 25 \(\sim 15\)			\(^{19}\) \(^{19}\) \(^{19}\)
59 Pr	0.45 and 0.04 C Slow	Ra \(\gamma\)—Be — —	3.5 ± 9.0 25		\((1.1 \pm 0.04)\,10^{-2}\)	\(^{19}\) Pr\(^{142}\) \(^{19}\) \(^{19}\)

Continuation

Element	$E_n$ in MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scatt}}$	$\sigma_{\mathrm{abs}}$	Note
60 Nd	5 eV	—	$\sim 20$			^102^
60 Nd	0.08 eV	—	$\sim 70$			^102^
60 Nd	Slow	—	220			^19^
60 Nd	"	—	65			^20^
60 Nd	Thermal	—	72			^91^
60 Nd	*	—		15	92	^102^
62 Sm	C	—	$5960 \pm 400$			^19^
62 Sm	0.096 eV	—	15500			^94^ Resonance
62 Sm	0′096 eV	—			93000	^93^ Sm^149^, reson. capture
62 Sm	Slow	—	4700			^19^ Sm$_2$O$_3$
62 Sm	"	—	6500–7300			^19^
62 Sm	Thermal	—	7040			^91^
63 Eu	0.45 and 0.04	Ra $\gamma$–Be			$(9.5 \pm 0.5)\,10^{-2}$	^19^ Eu^152,154^
63 Eu	22 eV	—	$>1100$			^94^ Resonance
63 Eu	9.2 eV	—	$>600$			^94^ "
63 Eu	3.3 eV	—	$>900$			^94^ "
63 Eu	0.54 eV	—			20000	^93^ Eu^153^, reson. capture
63 Eu	0.465 eV	—	5670			^94^ Eu^153^
63 Eu	C	—	$3810 \pm 360$			^19^
63 Eu	"	—	$4120 \pm 670$			^19^
63 Eu	"	—	$\sim 1000$			^19^ Calcul.
63 Eu	$<0.03$ eV	—			$>3000$	^93^ Eu^151^, reson. capture
63 Eu	Therm.	—	2700			^91^

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
64 Gd	\(0.2–0.003\ \mathrm{eV}\)	—	\(3000 \ldots 125\,000\)			\(^{116}\)
64 Gd	C	—	\(35\,700 \pm 3300\)			\(^{19}\)
64 Gd	*	—	\(2920 \pm 1850\)			\(^{19}\)
64 Gd	*	—	\(30000\)			\(^{19}\) \( \mathrm{Gd}_2\mathrm{O}_3\)
64 Gd	\(0.044\ \mathrm{eV}\)	—			\(190\,000\)	\(^{93}\) \( \mathrm{Gd}^{157}\), capture res.; \(\sigma_{\mathrm{capt.}}\mathrm{Gd}^{155}\) is \(\sim 3\) times \(< \sigma_{\mathrm{capt.}}\mathrm{Gd}^{157}\), \(^{115}\)
64 Gd	\(0.031\ \mathrm{eV}\)	—	\(44\,000\)			\(^{94}\)
64 Gd	Thermal	—	\(22\,550\)			\(^{91}\)
65 Tb	\(0.45\) and \(0.04\)	Ra \(\gamma\)—Be			\(0.18 \pm 0.02\)	\(^{19}\) \(\mathrm{Tb}^{160}\)
65 Tb	Thermal	—	\(15\)			\(^{91}\)
66 Dy	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D	\(>270\)		\(<0.007\)	\(^{19}\) \(\mathrm{Dy}^{164}\)
66 Dy	\(5.5\ \mathrm{eV}\)	—	\(>330\)			\(^{108}\) Resonance
66 Dy	\(1.74\ \mathrm{eV}\)	—	\(863 \pm 53\)			\(^{108}\)
66 Dy	C	—	\(400 \ldots 2100\)			\(^{19}\)
66 Dy	\(0.15–0.007\ \mathrm{eV}\)	—	\(780\)			\(^{116}\)
66 Dy	Slow	—				\(^{19}\)
66 Dy	*	—			\(745\)	\(^{20}\) \(\mathrm{Dy}_2\mathrm{O}_3\)
66 Dy	Thermal	—	\(\sim 1180\)			\(^{94}\)
66 Dy	*	—			\(725\)	\(^{67}\) \(\mathrm{Dy}^{164}+n^1=\mathrm{Dy}^{165}+\gamma\)
66 Dy	*	—			\(870\)	\(^{108}\) Capture
66 Dy	*	—	\(780\)			\(^{91}\)

Continuation

Element	\(E_n\) in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
67 Ho	\(C\) Therm.	— —	\(47 \pm 26\) 52			\(^{19}\) \(^{91}\)
68 Er	\(C\) Therm.	— —	\(233 \pm 46\) 165			\(^{19}\) \(^{91}\)
69 Tu	\(C\) Therm.	— —	\(69 \pm 26\) 114			\(^{19}\) \(^{91}\)
70 Yb	\(C\) Therm.	— —	\(46 \pm 28\) 50			\(^{19}\) \(^{91}\)
71 Cp	\(0.45\) and \(0.04\) \(C\) Slow	Ra \(\gamma\)—Be — —	\(99 \pm 27\) 165		\(0.17 \pm 0.01\)	\(^{19}\) Comp.\(^{17)}\) \(^{19}\) \(^{91}\)
72 Hf	Slow	—	\(175.4 \pm 29.0\)			\(^{86}\) HfO\(_2\)
73 Ta	\(37 \pm 3\) eV \(22 \pm 2\) eV \(10.0 \pm 0.3\) eV \(4.1 \pm 0.1\) eV 1 eV	— — — — —	\(>16\) \(>22\) \(>30\) \(>100\)	72		\(^{92}\) Resonance \(^{92}\) ” \(^{92}\) ” \(^{92}\) ” \(^{12}\) ”

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
73 Ta	\(< 1\ \mathrm{eV}\)	—	\(3.0\,E_n^{-1/2}+7.2\)	—	—	\(^{92}\)
73 Ta	Slow	—	27	10	—	\(^{19}\)
73 Ta	•	—	—	—	11.5	\(^{19}\)
73 Ta	•	—	—	—	20	\(^{20}\) \( \mathrm{H}_8\mathrm{Ta}_2\mathrm{O}_4 \)
73 Ta	•	—	—	—	20.6	\(^{20}\) \( \mathrm{Ta}^{181}+n^1=\mathrm{Ta}^{182}+\gamma \)
73 Ta	Thermal	—	—	—	0.034	\(^{104}\) \( \mathrm{Ta}^{181}+n^1=\mathrm{Ta}^{182}+\gamma \)
73 Ta	•	—	—	—	—
74 W	—	\(d-\mathrm{Li}\)	\(5.40 \pm 0.15\)	—	—	\(^{37}\)
74 W	2.8—2.1	\(d-\mathrm{D}\)	\(5.77 \ldots 6.10 \pm 0.19\)	—	—	\(^{28}\)
74 W	2.50—2.38	—	\(6.21 \pm 0.23\)	—	—	\(^{37}\)
74 W	0.860	RaTh \(\gamma\)—Be	—	\(6.8 \pm 0.9\)	—	\(^{33}\)
74 W	0.83	Nd\(^{24}\) \(\gamma\)—Be	7.7	—	—	\(^{47}\)
74 W	0.62	La\(^{14}\) \(\gamma\)—Be	7.8	—	—	\(^{47}\)
74 W	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	8.0	—	—	\(^{47}\)
74 W	\(0.22 \pm 0.04\)	ThC″ \(\gamma\)—D	—	—	\(2.6 \cdot 10^{-3}\)	\(^{19}\)
74 W	0.210	RaTh \(\gamma\)—D	—	\(9.0 \pm 0.7\)	—	\(^{33}\)
74 W	0.14	Mn\(^{56}\) \(\gamma\)—Be	9.4	—	—	\(^{47}\)
74 W	0.133 and 0.530	Rn \(\gamma\)—Be	—	\(9.7 \pm 0.7\)	—	\(^{77}\)
74 W	0.13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	10.0	—	—	\(^{47}\)
74 W	0.024	Sb\(^{124}\) \(\gamma\)—Be	13.8	—	—	\(^{47}\)
74 W	180 eV	—	\(>26\)	—	—	\(^{92}\) Resonance
74 W	45 eV	—	\(>28\)	—	—	\(^{92}\) ”
74 W	\(18.0 \pm 0.5\) eV	—	\(>200\)	—	—	\(^{92}\) ”
74 W	\(7.4 \pm 0.2\) eV	—	\(>34\)	—	—	\(^{92}\) ”
74 W	\(4.0 \pm 0.1\) eV	—	\(>80\)	—	—	\(^{92}\) ”

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
74 W	\(D\)	—		\(9.3 \pm 2\)		\(^{19}\)
74 W	\(< 1\ \mathrm{eV}\)	—	\(2.72\,E_n^{-1/2} + 5.7\)			\(^{92}\)
74 W	\(0.5\ \mathrm{eV}\)	—		\(5.7\)		\(^{12}\)
74 W	Thermal	—	\(23\)			\(^{19}\)
74 W	Thermal	—		\(7.8\)		\(^{19}\)
74 W	Thermal	—			\(20.4\)	\(^{30}\)
74 W	Thermal	—	\(17.5\)			\(^{20}\)
75 Re	Thermal	—	\(89\)			\(^{19}\)
75 Re	Thermal	—			\(104\)	\(^{30}\)
76 Os	\(20 \pm 1\ \mathrm{eV}\)	—	\(> 23\)			\(^{83}\) Resonance
76 Os	\(8.8 \pm 0.3\ \mathrm{eV}\)	—	\(> 50\)			\(^{88}\) Resonance
76 Os	\(6.5 \pm 0.3\ \mathrm{eV}\)	—	\(> 36\)			\(^{89}\) Resonance
76 Os	\(4\text{–}0.02\ \mathrm{eV}\)	—	\(2.7\,E_n^{-1/2} + 15\)			\(^{85}\)
76 Os	\(1\ \mathrm{eV}\)	—		\(10\)		\(^{12}\)
76 Os	Thermal	—	\(27\)			\(^{19}\)
76 Os	Thermal	—		\(10.8\)		\(^{19}\)
77 Ir	\(0.45\) and \(0.04\)	Ra \(\gamma\) — Be			\(0.13\) or \(0.20 \pm 0.006\)	\(^{19}\) Ir\(^{192}\), \(^{194}\)
77 Ir	\(14\ \mathrm{eV}\)	—	\(18 \pm 3\)			\(^{79}\)
77 Ir	\(6.0\ \mathrm{eV}\)	—	\(97\)			\(^{94}\) Resonance

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
77 Ir	\(3.5\text{—}2.2\ \mathrm{eV}\)	—	\(25\pm4\)			\(^{79}\)
77 Ir	\(1.35\ \mathrm{eV}\)	—	612			\(^{94}\) Resonance
77 Ir	\(1.29\ \mathrm{eV}\)	—	1880			\(^{97}\) ”
77 Ir	\(1.27\pm0.04\ \mathrm{eV}\)	—	\(>4000\)			\(^{79}\) ”
77 Ir	\(0.64\ \mathrm{eV}\)	—	\(>4500\)			\(^{79}\) ”
77 Ir	\(0.635\ \mathrm{eV}\)	—	543			\(^{94}\) ”
77 Ir	\(0.620\ \mathrm{eV}\)	—	2930			\(^{97}\) ”
77 Ir	Slow	—	410			\(^{19}\)
77 Ir	”	—	285			\(^{19}\)
77 Ir	”	—	325			\(^{20}\)
77 Ir	Thermal	—	\(64E_n^{-1/2}+14\)			\(^{79}\)
78 Pt	3.1	\(d\text{—}D\)		\(0.47\text{—}0.44\)		\(^{59}\) Inverse elastic scat.
78 Pt	\(1000\ \mathrm{eV}\)	—	\(>13\)			\(^{98}\) Resonance
78 Pt	\(100\ \mathrm{eV}\)	—	\(>15\)			\(^{92}\) ”
78 Pt	\(18.2\pm1\ \mathrm{eV}\)	—	\(>18\)			\(^{92}\) ”
78 Pt	\(11.5\pm0.4\ \mathrm{eV}\)	—	\(>30\)			\(^{92}\) ”
78 Pt	\(1\ \mathrm{eV}\)	—		12		\(^{12}\)
78 Pt	\(0.8\text{—}0.04\ \mathrm{eV}\)	—	\(1.03E_n^{-1/2}+12.0\)			\(^{92}\)
78 Pt	Slow	—	21.5	8.3		\(^{19}\)
78 Pt		—	25			\(^{19}\)

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Notes
79 Au	3,1	\(d-\mathrm{D}\)		0,59–0,50		\(^{59}\) back elastic scattering
79 Au	0,45 and 0,04	\(\mathrm{Ra}\gamma-\mathrm{Be}\)			\(0,13\pm0,00\) \(0,023\)	\(^{19}\) Au\(^{198}\)
79 Au	\(0,22\pm0,01\)	\(\mathrm{ThC}^{\prime\prime}\gamma-\mathrm{D}\)				\(^{19}\) Au\(^{197}\)
79 Au	5,4 eV	—	\(>21\)			\(^{94}\) resonance
79 Au	4,8 eV	—	60000			\(^{92}\) Au\(^{197}+n^1=\) Au\(^{198}\) \(r\gamma\), \(^{46}\) resonant capture
79 Au	4,8 + 0,2 eV	—	\(>240?\)			\(^{117},\,^{116}\)
79 Au	0,3–0,01 eV	—	\((14,9\pm0,3)\times E_n^{-1/2}\left(1+0,42E_n^{-1/2}\right)+\dfrac{(90\pm2)}{10^3}\)
79 Au	slow	—	103			\(^{19}\)
79 Au	slow	—	88		72	\(^{19}\)
79 Au	slow	—				\(^{19}\)
79 Au	slow	—	80			\(^{20}\)
79 Au	thermal	—	99,3			\(^{94}\)
79 Au	thermal	—	100			\(^{116}\) 300° abs.
79 Au	thermal	—	\(104\pm2\)			\(^{117}\) 300°
80 Hg	—	\(d-\mathrm{Li}\)	\(5,47\pm0,19\)			\(^{37}\) HgO
80 Hg	\(2,88\pm0,04\)	\(d-\mathrm{D}\)	\(5,34\pm0,20\)			\(^{39}\)
80 Hg	2,8–2,1	”	\(4,75;\ 5,27\pm1,22\)			\(^{29}\)
80 Hg	2,50–2,38	”	\(5,13\pm0,23\)			\(^{37}\) HgO

Continuation

Element	$E_n$ in MeV	Neutron source	$\sigma$	$\sigma_{\mathrm{scat}}$	$\sigma_{\mathrm{abs}}$	Note
80 Hg	0.860	RaTh$\gamma$—Be		$6.4 \pm 0.5$		33
80 Hg	0.210	RaTh$\gamma$—D		$7.8 \pm 0.6$		33
80 Hg	0.18 or 0.10	$d$—C	6.8			44
80 Hg	0.133 and 0.530	Rn$\gamma$—Be		$9.7 \pm 1.2$		77
80 Hg	2.5–0.02 eV	—	$6 + E_n^{-1/2} + 15$			46
80 Hg	$D$	—		$12.0 \pm 1.0$	$\dfrac{1180}{v}$	19
80 Hg	1–0.004 eV	—				81, $v$ in $\dfrac{\mathrm{km}}{\mathrm{sec}}$, capture
80 Hg	1–0 eV	—		15		12
80 Hg	C	—		28		19
80 Hg	Slow	—	355			19
80 Hg	”	—	380			19
80 Hg	”	—		5		19
80 Hg	”	—			325	20
80 Hg	”	—	450			20
80 Hg	”	—		4.7		20
80 Hg	”	—			3100	105 Hg$^{196}$ $(n,\gamma)$
80 Hg	”	—			2500	105 Hg$^{199}$ $(n,\gamma)$; $(n,2n)$
80 Hg	”	—			$<60$	105 Hg$^{200}$ $(\ldots,\gamma)$
80 Hg	”	—			$<60$	105 Hg$^{201}$ $(n,\gamma)$; $(n,2n)$
80 Hg	”	—			$<60$	105 Hg$^{202}$
80 Hg	”	—			$<60$	105 Hg$^{204}$

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
81 Tl	0.860	Ra\(^?\) γ—Be		\(6.7 \pm 1.2\)		\(^{33}\)
81 Tl	0.45 and 0.04	Ra γ—Be			\(0.013 \ldots 0.006\) \(\pm 0.003\) \(-0.001\)	\(^{19}\) Tl\(^ {204,206}\)
81 Tl	\(0.22 \pm 0.04\)	ThC″ γ—D				\(^{19}\)
81 Tl	0.210	RaTh γ—D		\(6.7 \pm 1.2\)		\(^{33}\)
81 Tl	0.133 and 0.530	Rn γ—Be		\(8.2 \pm 1.2\)		\(^{77}\)
81 Tl	1100 eV	—	\(> 12\)			\(^{83}\) Resonance
81 Tl	270 eV	—	\(> 15\)			\(^{83}\) ”
81 Tl	10–0.02 eV	—	\(0.6 E_n^{-1/2} + 9.7\)			\(^{83}\)
81 Tl	1 eV	—		9.7		\(^{12}\)
81 Tl	C	—			\(< 3.3\)	\(^{63}\) Tl\(^ {203}\)
81 Tl	•	—			0.17	\(^{64}\) Tl\(^ {203}\)
81 Tl	Slow	—	11			\(^{19}\)
81 Tl	”	—		14.2		\(^{19}\)
81 Tl	”	—			2.2	\(^{20}\)
81 Tl	”	—			3.2	\(^{20}\)
82 Pb	—	d—Li	\(5.10 \pm 0.13\)			\(^{37}\)
82 Pb	3.1	d—D		2.5–2.3		\(^{59}\) Reverse elastic scattering
82 Pb	\(2.68 \pm 0.04\)	”	\(6.74 \pm 0.24\)			\(^{39}\)
82 Pb	2.5	”		\(1.31 \pm 0.53\)		\(^{103}\) Inelastic scattering
82 Pb	2.5	”		\(0.63 \pm 0.2\)		\(^{107}\) ” ”
82 Pb	2.5	”	\(6.0 \pm 0.7\)			\(^{60}\)
82 Pb	2.5	”		\(9.2 \pm 0.6\) (45°)		\(^{60}\)

Continuation

Element	$E_n$ in MeV	Neutron source	$\varepsilon$	$\varepsilon_{\mathrm{scatt}}$	$\varepsilon_{\mathrm{abs}}$	Note
82 Pb	2.5	$d$ D		$3.1 \pm 0.8\ (100^\circ)$		60
82 Pb	2.5	"		$5.0 \pm 0.6\ (45^\circ)$		60 elastic and inelastic
82 Pb	2.5	"		$2.5 \pm 0.4\ (100^\circ)$		60 " "
82 Pb	2.50—2.38	"	$5.25 \pm 0.15$			37
82 Pb	—	"		$2.44\ (23^\circ)$		82
82 Pb	—	"		$1.67\ (33^\circ)$		82
82 Pb	—	"		$0.73\ (44^\circ)$		82
82 Pb	—	"		$0.17\ (55^\circ)$		82
82 Pb	0.860	RaTh $\gamma$—Be	$6.83 \pm 0.40$			29
82 Pb	0.860	"		$5.1 \pm 0.6$		33
82 Pb	0.83	Na$^{24}\gamma$—Be	5.8			47
82 Pb	0.62	La$^{140}\gamma$—Be	6.1			47
82 Pb	0.22	Na$^{24}\gamma$—D$_2$O	8.6			47
82 Pb	0.210	RaTh $\gamma$—D		$6.2 \pm 0.7$		83
82 Pb	0.18 or 0.10	$\alpha$—C	7.2			44
82 Pb	0.15	RaC $\gamma$—Be		$7.3 \pm 1.4$	$< 0.31$	73
82 Pb	0.14	Mn$^{56}\gamma$ Be	10.6			47
82 Pb	0.13	Ga$^{72}\gamma$—D$_2$O	10.6			47
82 Pb	0.024	Sb$^{124}\gamma$—Be	11.4			47
82 Pb	$D$	—	11.39			48
82 Pb	"	—		$9.8 \pm 0.8$		19
82 Pb	1 eV	—		12.5		12
82 Pb	$C$	—		5.0		19
82 Pb	Slow	—	12.5			19
82 Pb	"	—	8.6			19
82 Pb	"	—		12.9		19
82 Pb	"	—			0.32	20
82 Pb	"	—			$0.23 \pm 0.06$	70 Pb$_3$O$_4$, capture

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scat}}\)	\(\sigma_{\mathrm{abs}}\)	Note
82 Pb	M long.	—	10	9.0	·	\(^{20}\)
82 Pb	"	—	10	9.0		\(^{20}\)
82 Pb	"	—	10	9.0	0.8	\(^{20}\)
82 Pb	Therm.	—	10	9.0	\(2.5 \pm 0.2\)	\(^{19}\)
82 Pb	"	—	10	9.0	\(\sim 10^{-3}\)	\(^{108}\) Pb\(^{208}\)
82 Pb	"	—	10	9.0	\(< 7 \cdot 10^{-4}\)	\(^{108}\) Pb\(^{204}\)
82 Pb	"	—	10	9.0	\(< 1.7 \cdot 10^{-4}\)	\(^{109}\) Pb\(^{204}\), fission
82 Pb	"	—	10	9.0	\(< 1.1 \cdot 10^{-5}\)	\(^{109}\) Pb\(^{206}\), "
82 Pb	"	—	10	9.0	\(< 1.1 \cdot 10^{-5}\)	\(^{109}\) Pb\(^{207}\), "
82 Pb	"	—	10	9.0	\(< 5 \cdot 10^{-6}\)	\(^{109}\) Pb\(^{208}\), "
83 Bi	—	\(d\)—Li	\(5.23 \pm 0.22\)			\(^{37}\)
83 Bi	2.8—2.1	\(d\)—D	\(5.35—6.0 \pm 0.19^{*}\)			\(^{28}\)
83 Bi	2.50—2.38	"	\(6.30 \pm 0.21\)			\(^{37}\)
83 Bi	—	"		2.27 (22°)		\(^{82}\)
83 Bi	—	"		1.35 (33°)		\(^{82}\)
83 Bi	—	"		0.68 (44°)		\(^{82}\)
83 Bi	—	"		0.24 (55°)		\(^{82}\)
83 Bi	0.860	RaTh \(\gamma\)—Be		\(5.4 \pm 0.7\)		\(^{33}\)
83 Bi	0.83	Na\(^{24}\) \(\gamma\)—Be	5.9			\(^{47}\)
83 Bi	0.22	Na\(^{24}\) \(\gamma\)—D\(_2\)O	8.0			\(^{47}\)
83 Bi	0.210	RaTh \(\gamma\)—D		\(8.4 \pm 0.8\)		\(^{33}\)
83 Bi	0.18 or 0.10	\(d\)—C	7.7			\(^{44}\)
83 Bi	\(\sim 0.14\)	Mn\(^{56}\) \(\gamma\)—Be	9.7			\(^{47}\)

Continuation

Element	\(E_n\), in MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{scatt}}\)	\(\sigma_{\mathrm{abs}}\)	Note
83 Bi	0,133 and 0,530	Rn \(\gamma\)—Be		\(8,1 \pm 1,3\)		77
83 Bi	0,13	Ga\(^{72}\) \(\gamma\)—D\(_2\)O	10,2			47
83 Bi	0,024	Sb\(^{124}\) \(\gamma\)—Be	12,1			47
83 Bi	\(D\)	—		\(16 \pm 1\)		19
83 Bi	1 eV	—		9,2		12
83 Bi	\(1,0 > E_n > 0,5\) eV	—	8,34			19
83 Bi	\(C\)	—		9,2		19
83 Bi		—			\(< 0,1\)	63 Bi\(^{209}\)
83 Bi	Slow	—	8,9	8,9		19
83 Bi	”	—	8,2			19
83 Bi	”	—			0,33	20
83 Bi	”	—			0,45	20
83 Bi	Thermal	—			0,023	110 Bi\(^{209}\) + \(n^1\) = Bi\(^{210}\) + \(\gamma\)
83 Bi	”	—			\(\le 0,01\)	61 Threshold value, \(\sigma_{\mathrm{capt.}}\)
83 Bi	”	—			0,001	108 Bi\(^{209}\)
83 Bi	”	—			\(< 2.5 \cdot 10^{-6}\)	109 Bi\(^{208}\), fission
84 Po	Thermal	—			\(< 0,1\)	109 Po\(^{210}\), fission
90 Th	2,4	\(d\)—D			0,1	19 Fission
90 Th	0,18 or 0,10	\(d\)—C	\(7,3\)			19
90 Th	Slow	—			7,1	20 ThO\(_2\)
90 Th	Thermal	—			\(6,0 \pm 0,3\)	19

Continuation

Element	\(E_n\), MeV	Neutron source	\(\sigma\)	\(\sigma_{\mathrm{calc}}\)	\(\sigma_{\mathrm{abs}}\)	Note
92 U	2.4	\(d \to D\)	14.4		0.5	\(^{19}\) Fission
92 U	Fast neutrons	Ra \(\gamma\)–Be	\(6 \pm 2\)			\(^{19}\)
92 U	—	″	5			\(^{19}\)
92 U	—	Rn \(\gamma\)–Be			0.1	\(^{19}\) Fission
92 U	0.860	RaTh \(\gamma\)–Be	\(8.0 \pm 0.4\)			\(^{98}\)
92 U	0.18 or 0.10	\(d\)–C	17			\(^{19}\)
92 U	5 and 30 eV	—			5000	\(^{19}\) Reson. capture
92 U	Slow	—	\(23.1 \pm 0.5\)	\(12 \pm 3\)	\(1.1 \pm 0.3\)	\(^{19}\)
92 U	″	—			\(1.3 \pm 0.45\)	\(^{19}\)
92 U	″	—	23	12		\(^{20}\)
92 U	″	—			1.5	\(^{20}\)
92 U	Thermal	—	\(20 \pm 2\)	15	3	\(^{19}\)
92 U	″	—			2–3	\(^{19}\) Fission
92 U	″	—			2	\(^{19}\) UO\(_2\), fission
92 U	″	—			400–500	\(^{19}\) U\(^{235}\), ″
92 U	″	—	\(1.5 \pm 0.2\)			\(^{19}\) U\(^{238}\)
93 Np	3 to \(\sim\) thermal				1.5–0.0	\(^{111}\) Np\(^{237}\), fission, see Fig. 3
93 Np	0.890–0.375				1.2–0.1	\(^{112}\) Np\(^{237}\), fission
94 Pu	Slow					\(^{113}\) \(\sigma_d\) Pu\(^{239}\) \(>\) \(\sigma_d\) U\(^{235}\)

REFERENCES

1. Gamov, Zeits. f. Phys. 52, 510 (1929); Condon and Gurney, Phys. Rev. 33, 127 (1929); Konopinski and Bethe, Phys. Rev. 54, 150 (1938); Weisskopf and Ewing, Phys. Rev. 57, 472 (1940).

2. Oppenheimer and Phillips, Phys. Rev. 48, 500 (1935).

3. For a more rigorous solution of the problem of energy redistribution in elastic collisions, see Condon and Breit, Phys. Rev. 49, 229 (1936).

4. See, for example, Goudsmit, Phys. Rev. 49, 406 (1936).

5. Siborg, Usp. fiz. nauk 28, 285 (1946).

6. See, for example, Bethe, Rev. Mod. Phys. 9, 69 (1937); Livingston and Bethe, Rev. Mod. Phys. 9, 244 (1937).

7. Jentschke and Prankl, Zeits. f. Phys. 119, 696 (1942); Jentschke, Zeits. f. Phys. 120, 165 (1943); Journ. Amer. Chem. Soc. 68, 2411 (1946).

8. Anderson, Fermi and Hanstein, Phys. Rev. 55, 797 (1939) \((\nu \simeq 2)\); Anderson, Fermi and Szillard, Phys. Rev. 56, 284 (1939) \((\nu \simeq 1.5)\); Bradt, Helv. Phys. Acta 12, 553 (1939) \((\nu = 2.95 \pm 0.5)\); Haenny and Rosenberg, C. R. 208, 893 (1939) \((\nu > 1)\); Hagiwara, Rev. Phys. Chem. Japan 13, 145 (1939) \((\nu = 2.6)\); Halban, Joliot and Kowarski, Nature 143, 470 (1939) \((\nu = 3.5 \pm 0.7)\); Turner, Phys. Rev. 57, 334 (1940) \((\nu = 2.6 \pm 0.6)\); Michiels, Parry and Thomson, Nature 143, 760 (1939) \((\nu > 1)\); Szillard and Zinn, Phys. Rev. 55, 619 (1939) \((\nu = 2.3)\); Zinn and Szillard, Phys. Rev. 56, 619 (1939) \((\nu = 2.3)\).

9. Farwell, Segre and Wiegand, Phys. Rev. 71, 327 (1947); Tsien San-Tsiang, Ho Zahwei, Chastel and Vigneron, Phys. Rev. 71, 382 (1947); Wollan, Moak and Sawyer, Phys. Rev. 72, 447 (1947).

10. Bohr, Nature 137, 344 (1936); Bory and Kalckar, UPhN 20, 317 (1938).

11. Breit and Wigner, Phys. Rev. 49, 519 (1936); Bethe and Placzek, Phys. Rev. 51, 450 (1937); Kapur and Peierls, Proc. Roy. Soc. 166, 277 (1938); Siegert, Phys. Rev. 53, 750 (1939); Breit, Phys. Rev. 64, 472 (1946).

12. Feshbach, Peaslee and Weisskopf, Phys. Rev. 71, 145 (1947).

13. Zinn, Phys. Rev. 71, 752 (1947).

14. Moyer, Petersen and Schmidt, Phys. Rev. 69, 666 (1946); Dempster, Phys. Rev. 71, 829 (1947).

15. Sturm, Phys. Rev. 71, 757 (1947).

16. Bohr and Wheeler, Phys. Rev. 56, 426 (1939).

17. Kiema, Phys. Rev. 72, 88 (1947).

18. Weisskopf and Ewing, Phys. Rev. 57, 472 (1940).

19. Diebner, Herrmann and Grassmann, Phys. Zeits. 440 (1942).

20. Volz, Zeits. f. Phys. 121, 201 (1943).

21. Wattenberg, Phys. Rev. 71, 497 (1947).

22. See, for example, Amaldi and Fermi, Usp. fiz. nauk 17, 313 (1937).

23. Bohm and Richman, Phys. Rev. 71, 567 (1947).

24. Sherr, Phys. Rev. 68, 240 (1945).

25. Sleator, Phys. Rev. 72, 207 (1947).

26. Ageno, Amaldi, Bociarelli and Trabacchi, Phys. Rev. 71, 20 (1947).

27. Bailey, Bennett, Bergstralh, Nickolls and Williams, Phys. Rev. 70, 583 (1946).

28. Aoki, Proc. Phys. Math. Soc. Japan 21, 232 (1939).

29. Good and Scharff-Goldhaber, Phys. Rev. 59, 917 (1941).

30. Leipunsky, J. Phys. USSR 3, 23f (1940).

31. Goloborodko and Leipunsky, DAN 26, 41 (1940).

1. Fisch, Phys. Rev. 70, 589 (1946).
2. Goloborodko and Leipunskii, DAN 30, 703 (1941).
3. Schultz and Goldhaber, Phys. Rev. 67, 202 (1945).
4. Manley, Haworth and Luebke, Phys. Rev. 61, 152 (1942).
5. Rarita and Schwinger, Phys. Rev. 59, 436 (1941).
6. Kikuchi and Aoki, Proc. Phys.-Math. Soc. Japan 21, 75 (1939).
7. Nuckolls, Bailey, Bennett, Bergstralh, Richards and Williams, Phys. Rev. 70, 805 (1946).
8. Zinn, Seely and Cohen, Phys. Rev. 56, 260 (1939).
9. Staub and Stephens, Phys. Rev. 55, 131 (1939); Staub and Tatel, Phys. Rev. 58, 820 (1940).
10. Hudspeth and Dunlap, Phys. Rev. 57, 971 (1940).
11. Hall and Koontz, Phys. Rev. 72, 126 (1947).
12. Motz and Schwinger, Phys. Rev. 58, 26 (1940).
13. Amaldi, Bocciarelli, Rasetti and Trabacchi, Phys. Rev. 56, 881 (1939).
14. Perfil’eva and Fedorov, ZhETF 7, 691 (1937).
15. Havens and Rainwater, Phys. Rev. 70, 154 (1946).
16. Fields, Russel, Sachs and Wattenberg, Phys. Rev. 71, 508 (1947).
17. Marschall, Phys. Rev. 70, 107 (1946).
18. Fermi, Sturm and Sachs, Phys. Rev. 71, 589 (1947).
19. Anderson, Fermi, Wattenberg, Weil and Zinn, Phys. Rev. 72, 16 (1947).
20. Barshall, Battat and Bright, Phys. Rev. 70, 458 (1946).
21. Leipunsky, J. Phys. USSR 3, 231 (1940).
22. Sutton, McDaniel, Anderson and Lavatelli, Phys. Rev. 71, 272 (1947).
23. See also Manley, Haworth and Luebke, Phys. Rev. 69, 407 (1946).
24. Rainwater and Havens, Phys. Rev. 70, 136 (1946).
25. Bacher, Baker and McDaniel, Phys. Rev. 69, 443 (1946).
26. Fermi, Marshall and Marshall, Phys. Rev. 72, 193 (1947).
27. Sherr, Phys. Rev. 61, 724 (1942).
28. Manley, Agnew, Barshall, Bright, Coon, Graves, Jorgensen and Waldman, Phys. Rev. 70, 612 (1946).
29. Barshall and Ladenburg, Phys. Rev. 61, 129 (1942); Barshall, Ladenburg and Van Voorhis, Phys. Rev. 59, 917 (1941).
30. Muehlhause and Goldhaber, Phys. Rev. 70, 85 (1946).
31. Barshall and Battat, Phys. Rev. 70, 245 (1946).
32. O’Neal and Goldhaber, Phys. Rev. 59, 102 (1941).
33. Manley, Haworth and Luebke, Phys. Rev. 59, 109 (1941).
34. Hincks, Phys. Rev. 70, 770 (1946).
35. Seren, Moger and Sturm, Phys. Rev. 70, 561 (1946).
36. Seren, Freidlander and Turkel, 71, 463 (1947).
37. Graves and Coon, Phys. Rev. 70, 101 (1946).
38. Rasetti, Phys. Rev. 58, 869 (1940).
39. Coltman and Goldhaber, Phys. Rev. 69, 411 (1946).
40. Little, Long and Mandeville, Phys. Rev. 69, 414 (1946).
41. Seagondollar and Barshall, Phys. Rev. 72, 439 (1947).
42. Leipunskii, Rozenkevich and Timoshuk, ZhETF 7, 33 (1937).
43. Huber, Helv. Phys. Acta. 14, 163 (1941).
44. Coltman, Phys. Rev. 59, 917 (1941).
45. Goloborodko, DAN 30, 307 (1941).
46. Goloborodko, ZhETF 10, 376 (1940).
47. Seidl, Harris and Dansdorf, Phys. Rev. 72, 168 (1947).
48. Rainwater, Havens, Wu and Dunning, Phys. Rev. 71, 65 (1947).

1. Barbre and Goldhaber, Phys. Rev. 71, 141 (1947).
2. Manley, Berger and Gillette, Phys. Rev. 69, 254 (1946).
3. Kikuchi, Aoki and Watatuki, Proc. Phys.-Math. Soc. Japan 21, 410 (1939).
4. Wu, Rainwater and Havens, Phys. Rev. 71, 174 (1947).
5. Hanstein, Phys. Rev. 53, 489 (1941).
6. Nix and Clement, Phys. Rev. 68, 159 (1945).
7. Louteijung, Ann. Phys. 41, 177 (1942).
8. Goloborodko and Leipunskii, DAN 25, 7 (1939).
9. Freidlander, Seren and Turkel, Phys. Rev. 72, 23 (1947).
10. Riezler, Ann. Phys. 41, 193 (1912).
11. Seren, Freidlander and Turkel, Phys. Rev. 71, 454 (1947).
12. Bomke and Reddemann, Zeits. f. Phys. 120, 56 (1942).
13. Havens, Wu, Rainwater and Meaker, Phys. Rev. 71, 165 (1947).
14. Borst, Ulrich, Osborne and Hasbronck, Phys. Rev. 70, 557 (1946).
15. Sturm, Phys. Rev. 71, 757 (1947).
16. Gehlen, Zeits. f. Phys. 121, 268 (1943).
17. Zinn, Phys. Rev. 71, 752 (1947).
18. Sawyer, Wollan, Bernstein and Peterson, Phys. Rev. 72, 109 (1947).
19. Seren, Engelkemеir, Freidlander and Turkel, Phys. Rev. 71, 09 (1947).
20. Feshbach, Peaslee and Weisskopf, Phys. Rev. 71, 564 (1947).
21. Jones, Phys. Rev. 72, 362 (1947).
22. Katcoff, Phys. Rev. 71, 826 (1947).
23. Sturm and Arnold, Phys. Rev. 71, 556 (1947).
24. Meitner, Arciv Math. Astron. Fysik 27, A, No. 17 (1940).
25. Seren, Freidlander and Turkel, Phys. Rev. 72, 163 (1947).
26. Inghram, Hess and Hayden, Phys. Rev. 71, 561 (1947).
27. Dunlap and Little, Phys. Rev. 60, 693 (1941).
28. Nonaka, Phys. Rev. 59, 681 (1941).
29. Maurer und Ramm, Zeits. f. Phys. 119, 602 (1942).
30. Borst and Floyd, Phys. Rev. 70, 107 (1946).
31. Houtermans und Bartz, Naturwiss. 30, 788 (1942).
32. Klema, Phys. Rev. 72, 89 (1947).
33. Frisch, Phys. Rev. 71, 479 (1947).
34. Kennedy, Seaborg, Segre and Wahl, Phys. Rev. 70, 555 (1946).
35. Bethe, Phys. Rev. 57, 1125 (1940); see also Present, Phys. Rev. 60, 28 (1941).
36. Lapp, Van Horn and Dempster, Phys. Rev. 71, 745 (1947).
37. Brill and Lichtenberger, Phys. Rev. 72, 585 (1947).
38. McDaniel, Sutton, Lavatelli and Anderson, Phys. Rev. 72, 729 (1947).