MEETINGS AND CONFERENCES

SESSION OF THE USSR ACADEMY OF SCIENCES ON THE PEACEFUL USES OF ATOMIC ENERGY

From July 1 to 5, 1955, a session of the USSR Academy of Sciences devoted to the problems of the peaceful uses of atomic energy was held in Moscow.

More than 80 reports and communications were presented at the session. About 2,600 people took part in its work. Among the participants in the session was a large group of foreign scientists who had arrived at the invitation of the Presidium of the USSR Academy of Sciences from China, Poland, Czechoslovakia, Hungary, Bulgaria, Romania, the German Democratic Republic, the Korean People’s Democratic Republic, the Mongolian People’s Republic, India, Yugoslavia, Finland, Sweden, Japan, and other countries.

The plenary meeting of the session opened with a brief introductory address by the President of the USSR Academy of Sciences, A. N. Nesmeyanov. Four reports on problems of the greatest scientific importance were then heard: the report by V. S. Fursov, “Work of the USSR Academy of Sciences on uranium-graphite reactors”; the report by M. G. Meshcheryakov, “Investigation of nuclear processes at high energies in accelerators”; the report by A. P. Vinogradov, “Radiochemical investigations of the products of nuclear transformations under bombardment by high-energy particles”; and the report by V. A. Engel’gardt, “Results and prospects for the use of radioactive isotopes in biochemistry.”

Opening the session, A. N. Nesmeyanov first of all noted the enormous significance of the peaceful use of atomic energy for the further progress of mankind. Until now, people have made use, in essence, only of various forms of transformed solar energy. Now, however, the speaker declared, the time has come for humanity to create its own sun on Earth.

Since the proven reserves of nuclear fuel—uranium and thorium—exceed the reserves of coal and oil by a factor of 10–20 in energy terms, the broad use of atomic energy will free mankind from the impasse, which until recently seemed inevitable, associated with the limited and fairly rapid depletion of the reserves of carbonaceous fuel in the Earth’s crust. But still more remarkable possibilities are contained in the solution of the problem of the peaceful use of thermonuclear transformations, capable, for example, of making the hydrogen of water billions of times more concentrated a fuel than coal.

A. N. Nesmeyanov noted the enormous importance of the international exchange of experience accumulated in different countries in these fields of research, and, as an example of such exchange, pointed to the disinterested assistance rendered by the Soviet Union to China, Czechoslovakia, Poland, Romania, the GDR, Hungary, and Bulgaria in the development of atomic technology.

Having given a brief review of the achievements of Soviet scientists in the field of atomic power engineering and the use of radioactive isotopes, A. N. Nesmeyanov expressed the wish that the session would promote the broad use in science, technology, agriculture, and medicine of all the possibilities that nuclear science and industry already provide us today.

In conclusion, the President of the Academy of Sciences of the USSR expressed the hope that atomic and hydrogen weapons would be banned, and called upon the scientists of the entire world to engage in friendly joint work on the peaceful use of atomic energy.

In his report, V. S. Fursov gave a detailed account of the construction of the first Soviet atomic reactor, which at the same time proved to be the first atomic reactor in Europe.

The reactor was built with unenriched natural uranium. Graphite in the form of bricks (prisms) measuring \(100 \times 100 \times 600\) mm\(^3\) was used as the moderator. In the bricks forming the active zone, holes were drilled at a distance of 200 mm from one another for the uranium blocks (30–40 mm in diameter). The active zone—a sphere of radius 3 m—was surrounded on all sides by a graphite reflector 800 mm thick.

A steady chain reaction began in the 54th layer of graphite bricks inside the active zone. At that moment the reactor contained about 45 tons of natural uranium. Control of the course of the chain process was carried out by means of three cadmium rods.

Initially the reactor operated at a power of about 10 W. Later it was found that the boiler was completely explosion-safe, for with an increase in power the effective neutron multiplication factor in it rapidly decreased as a result of heating. This made it possible, even in the absence of a cooling system, to bring the boiler’s power for short periods up to several thousand kilowatts.

The creation of this reactor was a very difficult task. It is enough to point out, for example, that the physicists of Germany, on the basis of their measurements, came to the erroneous conclusion that it was impossible to build an atomic reactor using natural uranium and graphite, and, as is known, attempted to build a reactor using heavy water.

The start-up of the first nuclear reactor made it possible to carry out a number of extremely important studies to determine the temperature coefficient of reactivity of the boiler, the number of secondary neutrons arising per thermal neutron absorbed in the reactor substance, to study the resonance absorption of neutrons in uranium blocks, and so on.

The experience thus obtained made it possible to proceed to the construction of more powerful and more advanced reactors. Among such reactors is the RFT physicotechnical reactor, intended for physical experiments, the production of artificial radioactive isotopes, and the study of the construction of heat-releasing elements of power reactors.

The RFT reactor operates on uranium enriched with the fissionable isotope U\(^{235}\), and graphite; the cooling is water. The active zone is made in the form of a cylinder 1 m in diameter and height. The maximum power is 10,000 kW; in this case the flux of thermal neutrons at the center of the reactor is \(8 \cdot 10^{13}\) neutrons·cm\(^{-2}\)·sec\(^{-1}\).

The start-up of the RFT reactor made it possible to carry out a series of measurements of fission cross sections of various nuclei as a function of neutron energy, and also to study the behavior of various materials (uranium, graphite, steels, etc.) in strong fields of neutron and \(\gamma\)-radiation arising inside the reactor during its operation. The results of these studies were used, in particular, in designing the reactor of the industrial atomic power station of the Academy of Sciences of the USSR.

M. G. Meshcheryakov spoke about investigations of various nuclear processes with the aid of the synchrocyclotron of the Institute for Nuclear Problems of the Academy of Sciences of the USSR and the synchrotron of the P. N. Lebedev Physical Institute

MEETINGS AND CONFERENCES

of the Academy of Sciences of the USSR. Built under the direction of D. V. Efremov, M. G. Meshcheryakov, and A. L. Mints in 1949, the synchrocyclotron makes it possible to obtain protons with an energy of 680 MeV, charged \(\pi\)-mesons with an energy up to 400 MeV, and neutrons with an energy up to 600 MeV, as well as deuterons with an energy of 42 MeV and \(\alpha\)-particles with an energy of 840 MeV.

The synchrotron put into operation in the same year under the direction of V. I. Veksler and A. P. Komar accelerates electrons to 250 MeV.

The work carried out on the synchrocyclotron falls into the following four groups:

1) study of the elastic scattering of protons by protons, neutrons by neutrons, and neutrons by protons,

2) study of the formation of charged and neutral \(\pi\)-mesons in collisions of nucleons with nucleons,

3) investigation of the interaction of \(\pi\)-mesons with nucleons,

4) investigation of the interaction of nucleons and \(\pi\)-mesons with atomic nuclei.

In the work on the synchrotron, the processes of formation of \(\pi\)-mesons and the splitting of atomic nuclei by high-energy \(\gamma\)-quanta were studied.

The data obtained confirmed the validity of the hypothesis of charge symmetry of nuclear forces (the equivalence of the nuclear interaction of any pair of nucleons) in the indicated region of high energies of the bombarding particles. It proved possible to extend the validity of this hypothesis also to the region of meson phenomena: observations showed that the probability of formation of \(\pi^+\)- and \(\pi^-\)-mesons in collisions of neutrons with protons is the same, while the formation of \(\pi^0\)-mesons is forbidden both in a collision of two neutrons and in a collision of two protons. It was established that the process of charge exchange of nucleons in collisions is often also accompanied by an exchange of spins. Determination of the proton radius from scattering experiments led to a value of \(5 \cdot 10^{-14}\) cm, which is almost three times smaller than the radius of action of nuclear forces in meson theories. Apparently, the energies of the bombarding particles proved sufficient for penetrating inside the meson cloud surrounding the proton and for investigating the structure of this elementary particle.

Measurements of the energy dependence of the cross sections for scattering of \(\pi\)-mesons by nucleons and for photoproduction of \(\pi\)-mesons on nucleons revealed a nonmonotonic character in the change of the cross sections with increasing energy and indicated the existence of a maximum near 300 MeV. It is possible that this testifies to the existence of short-lived excited nucleons with an energy approximately 300 MeV above the ground state of the proton.

The results obtained, together with data from experiments on powerful accelerators in the USA, make the very concept of the elementary nature of the proton and neutron increasingly conditional, and indicate that nucleons as well are complex structures with respect to formations.

A. P. Vinogradov gave a detailed account of the results of radiochemical studies of the products of various nuclear transformations arising when nuclei are bombarded by high-energy particles. Bombardment of U, Th, Bi, W, Ag, Cu nuclei with particles of energy up to 680 MeV and study of the products obtained in these reactions showed that, along with the fission of nuclei into fragments, reactions also occur as a result of which the bombarded nucleus emits a certain number of neutrons and protons, as well as light nuclei. Such a process was called the splitting of atomic nuclei. It is accompanied by the appearance of many radioisotopes, with a deficiency or excess of neutrons, previously unknown to radiochemists; the study of their properties and mutual transformations considerably enriches our ideas about the nature of atomic nuclei. The table presented in the report gave data on 18 new isotopes discovered in the course of the investigations described (\(\mathrm{Sr}^{82-83}\), \(\mathrm{Ag}^{103}\), \(\mathrm{Cd}^{104-105}\), \(\mathrm{Hg}^{191-193}\), etc.). Among them, the ma-

humanity possesses the capacity for \(K\)-capture and positron activity. The study of such nuclear phenomena has brought us close to understanding nuclear processes which, on an enormous scale, occur in cosmic space, and has paved the way to those grand generalizations that lead to the establishment of the structure of nuclei, the ways in which they are formed, and the reasons for their varying abundance in the universe.

A. E. Engельгардт spoke about work in the field of biological chemistry carried out with the aid of labeled atoms.

Using two processes as examples—alcoholic fermentation and the synthesis of urea—he characterized the enormous possibilities of the labeled-atom method as applied to biochemistry, and reminded the audience of a number of very major scientific achievements obtained along this path. Labeled atoms made it possible for the first time to establish the existence of continuous renewal in various tissues of the living organism, down to the bones of the skeleton, the dentin of the teeth, and reserve fat deposits. It turned out, for example, that liver fats are renewed by half within twenty-four hours, and the reserve fats of the organism within a week. The existence of continuous exchange of proteins in all organs and tissues has also been reliably established.

Next, studies were noted that are being conducted in three extremely important directions. The first of these is the study, with the aid of radioactive carbon \(C^{14}\), of the processes of photosynthesis, which are the key to increasing humanity’s food resources. Here, in particular, it was possible to establish that the primary photochemical act associated with the absorption of quanta of ultraviolet radiation from the Sun is not the splitting of molecules of carbon dioxide, but the splitting of water molecules. As a result, it turned out that the oxygen released by plants is borrowed not from \(CO_2\) molecules, but from \(H_2O\) molecules. As for the carbon nutrition of plants, it is carried out not only at the expense of carbon from the air, but also at the expense of soil carbon, which until recently seemed simply incredible.

The second direction is connected with the study of the intimate biochemical processes occurring in the central nervous system in its various functional states, such as rest and activity, excitation and inhibition. Work in this direction is being successfully carried out in Moscow, in Ukraine, in Leningrad, and in Minsk. The use of radiophosphorus has made it possible to reveal the nature of the relationships among the principal processes of energy metabolism and the formation of phosphoproteins—the most chemically mobile fraction of the proteins of brain tissue. The chemical transformations undergone by lipoid compounds and nucleic acids—extremely important constituent elements of brain cells—have been investigated. It has been established, in particular, that the breakdown and synthesis of proteins in brain cells proceed very actively during normal activity of the nervous system (moderate excitation) and are sharply inhibited during overexcitation.

The third direction is the study of the metabolism of the cells of a cancerous tumor, which is the most formidable and stubborn enemy of human health. Here, too, very valuable and encouraging results have been obtained.

The further work of the session proceeded separately in four divisions: the physical-mathematical, chemical, biological, and technical sciences.

At the meetings of the Division of Physical and Mathematical Sciences, 21 reports were heard.

A number of reports were devoted to the results of studying various processes occurring in lattices of uranium and graphite. These works are of great value for the design of uranium-graphite atomic reactors.

For the design of atomic reactors an extremely important quantity is the neutron multiplication factor \(k\). For an infinite multiplying medium its value is determined by the formula

\[ k_\infty = \nu_{эф}\varphi\theta, \]

where $\nu_{\mathrm{eff}}$ is the number of fast neutrons arising upon the capture of one thermal neutron, $\varphi$ is the probability that the neutron will slow down to thermal velocities without capture, and $\theta$ is the fraction of thermal neutrons captured by fissioning nuclei. The condition for the existence of an undamped chain process is $k>1$.

In the report by L. V. Groshev, E. L. Feinberg, and I. M. Frank, “Neutron multiplication in uranium–graphite systems,” a number of general considerations were presented as an introduction to experimental investigations of the physical characteristics of neutron multiplication processes in systems made of uranium and graphite. Theoretical data were given for calculating the quantities $k_{\infty}$ and $\theta$, as well as the parameter $\chi$, which determines the critical radius of the system. The effects of air gaps or a layer of water around the blocks, required for air or water cooling of the reactor, were considered, as were the temperature effects of the reactor.

Measurements of the indicated quantities were carried out on subcritical reactor models—prisms made of uranium and graphite. The main investigations were carried out on a prism measuring $180 \times 180 \times 420\ \text{cm}^3$, containing 20 t of graphite and up to 7 t of uranium in the form of blocks.

Detailed data on the results of the experimental determination of $\chi$, $\theta$, and $k$, as well as on the influence of air gaps and the water surroundings of uranium blocks, depending on the character of the uranium–graphite lattice, were given in the report by L. V. Groshev, O. I. Kozintsa, L. E. Lazareva, K. D. Tolstov, E. L. Feinberg, I. M. Frank, F. L. Shapiro, and I. V. Shtranikh, “Study of the parameters of uranium–graphite heterogeneous systems by the prism method.”

Experiments with the first uranium–graphite reactor of the Academy of Sciences of the USSR indicated the presence of a strong dependence between the multiplication factor and the reactor temperature. Knowledge of this dependence is especially important for power atomic reactors operating at comparatively high temperatures. In view of the difficulty of obtaining the necessary data theoretically, it was again necessary here to make use of uranium–graphite prisms. In the report by B. P. Adlyasevich, O. I. Kozintsa, K. D. Tolstov, I. M. Frank, F. L. Shapiro, and I. V. Shtranikh, “Measurement of temperature effects in uranium–graphite subcritical systems,” separate data were presented on the influence of temperature on the quantities $\nu$, $\varphi$, $\theta$, and $k$. The estimates given in the report of the temperature effect for $k_{\mathrm{eff}}$ for three low-power reactors—the Academy of Sciences of the USSR reactor, GLEEP, and the argon reactor—agree well, within the limits of accuracy, with experimentally measured data.

No less important for the design of atomic reactors is knowledge of the energy spectrum and the mean velocities of neutrons in various media. However, the theoretical calculation of these quantities proves to be very difficult even in the simplest case of a homogeneous moderator. Therefore, here too it is necessary to use purely experimental results. On the measurements of the mean velocities of neutrons in various media, a report was presented at the session by K. D. Tolstov, F. L. Shapiro, and I. V. Shtranikh. Experiments were carried out both with homogeneous neutron moderators (graphite, paraffin, water) and with heterogeneous moderators (uranium–graphite of various concentrations at different temperatures, copper–graphite and water–neutron-absorber blocks). The mean neutron velocity $v$ and the mean value of $\sqrt{v}$, the diffusion length, and the neutron diffusion coefficient at different temperatures were determined, as well as the temperature dependence of the so-called transport length of neutrons. It was found that in homogeneous media an equilibrium Maxwellian velocity spectrum is established, whereas in heterogeneous systems the spectrum differs from a Maxwellian one: with reduced mean values compared with a homogeneous system characterized by the same ratio of numbers

atoms of absorber and moderator. Measurements were also made of the spectra of neutrons emitted from the surfaces of the media studied.

The report by M. B. Egi azarov, V. S. Dikarev, and V. G. Maleev, “Measurement of the resonance absorption of neutrons in a uranium-graphite lattice,” was devoted to a very important effect—the capture of neutrons by \(U^{238}\) nuclei, not accompanied by fission (the determination of the quantity \(1-\varphi\)). Since this phenomenon has a resonance character, it substantially affects the course of the chain reaction in a boiler, reducing the fraction of neutrons participating in this reaction. Also important is the fact that, as a result of neutron capture by \(U^{238}\) nuclei, a new nuclear fuel—\(Pu^{239}\)—is formed. In the work of M. B. Egi azarov et al., carried out at the first reactor of the Academy of Sciences of the USSR, careful measurements were made of the magnitude of the resonance absorption of neutrons as a function of the design and dimensions of the uranium blocks. The semi-empirical formulas thus obtained for the dependence of the probability of resonance absorption on the block diameter and the lattice pitch make it possible to estimate this effect in the design of reactors.

The same effect, but as applied to reactors of another type (uranium—heavy water), was studied by N. A. Burgov on the experimental heavy-water reactor of the Academy of Sciences of the USSR. The results of the investigations were summarized in the report “Resonance absorption of neutrons in heterogeneous systems.” For a constant lattice with \(a=9\ \mathrm{cm}\) and radius of the uranium rods \(p=1.1\ \mathrm{cm}\) (the rods were covered with a layer of aluminum \(0.1\ \mathrm{cm}\) thick), the following was obtained:

\[ k_{\infty}=1.183\pm0.008 \quad \text{and} \quad \varphi=0.875\pm0.010 . \]

For the successful solution of many important problems, the creation of nuclear reactors with ordinary-water moderators proves to be extremely promising. Several reports at the session were devoted to the consideration of various types of such reactors.

In the report by S. M. Feinberg, “Certain questions in the theory of the uranium-water lattice,” the features of a reactor with a moderator of ordinary water under pressure, operating on thermal neutrons, were considered. The simplicity of the design and the broad use in thermal-power installations of a water coolant under pressure create great technical and economic prospects for the application of such reactors in peaceful power engineering. In the report by S. M. Feinberg, the results of theoretical and experimental studies of the features of the uranium-water lattice are given: a considerable contribution (in comparison with uranium-graphite lattices) of fission of \(U^{238}\) nuclei by fast neutrons is shown; the slowing-down length of the neutron (i.e., the path length traversed by the neutron in the course of slowing down to thermal velocities) and the multiplication coefficient are determined.

The method of measuring the fast-neutron multiplication coefficient in uranium-water lattices was described in detail in the report by G. A. Stolyarov, L. V. Komissarov, V. P. Katkov, and Yu. V. Nikolsky.

In the extremely interesting report by G. N. Flerov, “Work of the Academy of Sciences of the USSR on reactors with uranium-235, plutonium-239, and a hydrogen moderator,” data were presented on the investigation of small nuclear reactors with hydrogen-containing moderators (ordinary water, polyethylene) at various concentrations of nuclear fuel. The work was carried out with reactors of two types: in some, the active material was dissolved in water; in others, plates of the active material alternated with plates of the moderator. The active zone of solution reactors was made in the form of a sphere of aluminum or stainless steel, with a diameter from 15 to \(30\ \mathrm{cm}\). The reactors operated stably at a power of \(1\text{–}3\ \mathrm{W}\), producing neutron fluxes with an intensity up to \(10^{10}\text{–}10^{11}\ \text{neutrons/sec}\). In concentrated-

... reactors the active zone had a cylindrical shape; the power was briefly brought up to 50 W.

The experiments carried out confirmed the presence of a number of advantages in solution-type reactors. They are small in size, can easily be built, possess a rigid self-regulation that ensures complete explosion safety in operation, require considerably less concrete for biological shielding. Small reactors of this type can serve as excellent neutron sources for experimental purposes, as well as for the production of radioactive isotopes easily extracted by chemical methods directly from the aqueous solution. Solution reactors have no blocks, the instability of which strongly affects reactor operation; they make it possible to remove substantially more heat per unit weight of active material and to achieve large depths of “burnup” of fissile materials. As a result, such a type of reactor can be successfully used for power purposes.

G. I. Marchuk reported on approximate methods for calculating nuclear reactors of various types both in the presence and in the absence of hydrogen-containing moderators.

Another group of papers presented at the session concerned the study of the elementary act of interaction of neutrons with the nuclei of fissile isotopes.

In the paper by V. I. Kalashnikova, V. P. Zakharova, A. V. Krasnushkin, V. I. Lebedev, L. A. Mikazyan, P. E. Spivak and M. I. Pevzner, “Measurements of the Average Number of Neutrons Emitted in the Fission of Various Isotopes of Uranium and Plutonium,” an account was given of work to determine the value \(\nu\)—the average number of secondary neutrons arising in one fission event under the action of thermal neutrons. Measurements were made on the isotopes \(U^{233}\), \(U^{235}\), \(Pu^{239}\) and \(Pu^{241}\) by the method of simultaneous registration of fission events in the substance under study and of the neutrons emitted in this process. With an accuracy up to 4%, the values obtained for \(\nu\) are: for \(U^{233}\), 2.6; for \(U^{235}\), 2.5; for \(Pu^{239}\), 3.0; and for \(Pu^{241}\), 3.1. In these same experiments it was shown that the values of \(\nu\) depend on the excitation energy of the fissile nucleus and can increase appreciably with increasing excitation energy.

For the real chain process in a nuclear reactor, what is important is the effective number of secondary neutrons \(\nu_{\mathrm{eff}}\), i.e., the number of neutrons produced in a given medium per one absorbed thermal neutron. The dependence of \(\nu_{\mathrm{eff}}\) on the energy of the captured primary neutrons causing fission was discussed in the paper by S. Ya. Nikitin, S. I. Sukhoruchkin, K. G. Ignat’ev, N. D. Galanina, P. A. Krupchitskii and V. F. Belkin. The determination of the energy dependence of \(\nu_{\mathrm{eff}}\) was carried out on a 128-channel neutron selector with a pulsed cyclotron beam, by simultaneously observing two effects: neutron absorption and fission—in one and the same sample. For measurements with neutrons of intermediate energies, a neutron-energy “transformer” was used—an aluminum tank containing 100 liters of heavy water, into which a square lattice of boron rods was lowered. The spectrum of neutrons from the “transformer” lay in the range 0.5–1000 eV. The results obtained for \(U^{233}\), \(U^{235}\), and \(Pu^{239}\) testify to a strong dependence of \(\nu_{\mathrm{eff}}\) on the energy of the fission-producing neutrons.

A short communication by B. G. Erozolimskii was devoted to the same question; he described the results of measurements of \(\nu_{\mathrm{eff}}\) for \(U^{233}\), \(U^{235}\), and \(Pu^{239}\) in a neutron beam from the RFT reactor with energies in the range from 0.2 to 100 eV, carried out by B. G. Erozolimskii, P. E. Spivak, G. A. Dorofeev and V. N. Lavrenchenko.

Interesting data on the determination of neutron yields in the fission of uranium and thorium by high-energy \(\gamma\)-quanta were reported in the paper by L. E. Lazareva, B. I. Gavrilov, B. N. Valuev,

G. N. Zatsepin and V. S. Stavinskii. The source of $\gamma$-quanta was a 30 MeV synchrotron; the fast neutrons produced in photodisintegration were slowed in paraffin and registered by an ionization chamber with $\mathrm{BF}_3$ in the intervals between the synchrotron $\gamma$-pulses. The values obtained for $\nu$ were $\sim 6$ for uranium and $\sim 14$ for thorium (at $E_n \sim 20$ MeV).

Several works considered at the sessions of the physics-and-mathematics section were devoted to questions of nuclear spectroscopy.

Using a magnetic spectrometer with double focusing in direction, possessing good resolving power (peak half-width 7.5 keV) and considerable luminosity ($2 \cdot 10^{-4}$ of $4\pi$), L. L. Gol’din, E. F. Tret’yakov and G. I. Novikova studied the $\alpha$-spectra of a number of heavy isotopes: $\mathrm{U}^{233}$, $\mathrm{U}^{234}$, $\mathrm{Pu}^{238}$, $\mathrm{Pu}^{239}$, $\mathrm{Pu}^{240}$, $\mathrm{Am}^{241}$ and $\mathrm{Pa}^{231}$. The data obtained indicate the existence of a number of unknown earlier energy levels and otherwise are in good agreement with the data of other authors. On the basis of these data, schemes of the energy levels of the daughter nuclei $\mathrm{Th}^{229}$, $\mathrm{Np}^{237}$ and $\mathrm{Ac}^{227}$ have been constructed.

By studying with a $\beta$-spectrometer the electron spectra of $\mathrm{U}^{237}$, $\mathrm{Am}^{241}$ and $\mathrm{Am}^{242}_{m}$, S. A. Baranov and K. N. Shlyagin determined the energy levels of the nucleus $\mathrm{Np}^{237}$ and established a new decay scheme of the isomeric nucleus $\mathrm{Am}^{242}_{m}$, differing substantially from the data of Goldhaber and Hill, and also of Seaborg.

In the report by B. P. Ad’yasevich, L. V. Groshev and A. M. Demidov, “Spectra of $\gamma$-rays upon neutron capture in certain heavy nuclei,” the results of measurements of $\gamma$-spectra arising upon capture of thermal neutrons by the nuclei Cd, Sm, Hg and Pb, irradiated in the RFT reactor, were presented. For the measurements a magnetic spectrometer was used, determining the energy of $\gamma$-rays from the energy of recoil electrons (Compton electrons) produced by $\gamma$-rays in a thin radiator. The data obtained contain valuable information on the radiative properties of nuclei and on their excited levels (energy, spin, parity).

Yu. G. Abov described a high-luminosity neutron crystal spectrometer of the Academy of Sciences of the USSR, designed and built by him, with a bent quartz single crystal. The operating energy interval of the spectrometer is $\sim 2$ eV. In the spectrometer a new, more advanced type of crystal holder was used, making it possible to bend large plates of single crystals without the occurrence of harmful side effects.

In the report by V. S. Fursov it was noted that, under the influence of powerful fluxes of neutrons and $\gamma$-rays in an atomic reactor, the physical properties (volume, electrical conductivity, thermal conductivity, etc.) of the materials located in it change sharply. On changes in the properties of graphite taking place under the action of irradiation in reactors, a detailed communication was made by V. I. Klimenkov and Yu. N. Alekseenko. The authors carried out studies of the specific volume, electrical resistance, thermal conductivity and mechanical properties of graphite irradiated under various conditions. Using data from X-ray structural studies, the authors describe an attempt to give a mechanism of radiation damage to the crystal lattice of graphite, based on the displacement of graphite atoms from their normal positions in the lattice under the action of fast neutrons and the formation of a peculiar solid solution of carbon in the graphite lattice by atoms located in metastable interstitial positions.

E. K. Zavoiskii and B. V. Ershler reported on the phenomenon they had studied of a sharp increase in the rate of diffusion of silver in lithium upon irradiation of the latter with thermal neutrons. In the experiment described by them, irradiation with a neutron flux of density $10^{12}$ neutrons$\cdot\mathrm{cm}^{-2}\cdot\mathrm{sec}^{-1}$ proved, with respect to the increase in the diffusion rate, equivalent to raising the temperature from 16 to $140^\circ$C. In the authors’ opinion, the increase in the diffusion rate is connected with the growth in the number of defects in the lithium lattice under the influence

bombardment by He⁴ and H³ nuclei arising in the reactions Li⁶(n, α)H³ and Li⁷(n, 2α).

The production of atomic energy is accompanied by the appearance of radioactive radiations dangerous to health. Therefore, the urgent necessity arises of creating dosimetric instruments that monitor the magnitude of the radiation dose received by a person.

This question was the subject of the report by V. V. Antonov-Romanovsky and I. B. Keirim-Markus, M. S. Poroshina, and Z. A. Trapeznikova, “Dosimetry of Radioactive Radiations with the Aid of Flash Phosphors,” containing a description of a new individual method of luminescent dosimetric control (ILK).

The method of measuring dose with the ILK dosimeter is based on determining the brightness of the flash of a specially developed phosphor SrS–Eu, Sm, excited by γ-rays, under the action of infrared light. In addition to γ-rays, the ILK dosimeter is also suitable for dosimetry of β-rays of thermal neutrons. The range of determinable doses for γ-radiation lies in the interval from 0.005 to 1000 r. This makes it possible to use ILK dosimeters not only for individual monitoring, but also for monitoring doses received over the course of two weeks, and for emergency work. A check of the readings of one dosimeter takes no more than a minute. The method is simple and does not require the expenditure of special materials.

At the sessions of the Division of Chemical Sciences, 18 reports were heard, thematically falling into three groups:

1) the study of products of fission and splitting of atomic nuclei by particles of high energies;

2) investigation of the influence of nuclear radiations on various substances and on the course of chemical processes;

3) the use of labeled atoms for studying the structure of chemical compounds and the kinetics of chemical reactions.

The report by A. P. Vinogradov, I. P. Alimarin, V. I. Baranov, A. K. Lavrukhina, T. V. Baranova, F. I. Pavlotskaya, A. A. Bragin, and Yu. V. Yakovlev, “Radiochemical Study of the Fission of Bismuth, Thorium, and Uranium under the Action of Protons with an Energy of 480 MeV,” contains data from the isolation and identification, carried out in 1951–1952, of the fission products of the indicated elements. Targets of the substances under study were irradiated in the internal beam of the synchrocyclotron of the Institute of Nuclear Problems of the Academy of Sciences of the USSR for approximately an hour. Radioactive isotopes of 36 elements were isolated from the irradiated targets. Identification of the isotopes was carried out according to the magnitudes of half-life periods, the energy, and the nature of the radioactive radiations.

Among the fission products new radioactive isotopes were found. It was established that the distribution of fragment yields is not double-humped, but has a single symmetrical curve. The radioactive fragments obtained do not have the long decay chains observed for fission products at low energies, and exhibit, as a rule, positron activity and the ability for K-capture. It is evident that the fission reaction is accompanied by intensive emission of neutrons. The fission cross sections of U and Th are close to the geometrical ones, while the fission cross section of Bi is considerably smaller than the geometrical one and equals 0.7·10⁻²⁷ cm². It was also established that fission of the Bi nucleus occurs, on the average, after the emission of 2 protons and 16 neutrons, i.e., the fission mechanism proves to be explicitly emissive: fission is preceded by the emission of several nucleons (chiefly neutrons), until a nucleus arises with a parameter \(Z^2/A\), close to the critical one, which then undergoes fission.

In the report by B. V. Kurchatov, R. N. Mekhedov, M. Ya. Kuznetsova, and L. N. Kurchatova, the fission products of tungsten nuclei by deuterons with an energy of 280 MeV were considered. The study of the fission products

showed that in these experiments, alongside the emission mechanism of fission, another mechanism also plays a significant role—fission from an excited level, especially important for nuclei of medium atomic weight. In this case, a strongly excited fissioning nucleus is formed with the production of excited fragments that subsequently emit several nucleons. The formation of nuclei \(\mathrm{Se}^{73}\) and \(\mathrm{Mo}^{90}\), which have a relatively high yield, has not yet received any explanation and requires further study.

In three other reports, the products of nuclear-reaction spallation occurring on various nuclei were considered. The investigations were carried out by radiochemical methods.

A. P. Vinogradov, I. P. Alimarin, V. I. Baranov, A. K. Lavrukhina, T. V. Baranova, and F. I. Pavlotskaya investigated the spallation products of Cu nuclei under bombardment by deuterons with an energy of 280 MeV and by protons of 480 and 680 MeV, and of Bi nuclei under bombardment by protons of 480 MeV.

A. N. Murin, B. K. Preobrazhenskii, I. A. Iutlandov, and M. A. Yakimov studied the products of spallation and fission reactions on Cu, La, and Bi nuclei under the action of protons with energies of 480 and 660 MeV. Reactions of the type \(\mathrm{Cu}^{63}(p; 3p, 5n)\mathrm{Co}^{55}\), \(\mathrm{Cu}^{65}(p; 4\alpha, 2p, n)\mathrm{Ca}^{47}\) were considered. The possibility of carrying out the reaction \(\mathrm{Bi}^{209}(p; 13n, 24n)\mathrm{Ce}^{134}\) was discussed.

B. V. Kurchatov, V. N. Mekhedov, N. I. Borisova, M. Ya. Kuznetsova, L. N. Kurchatova, and L. V. Chistiakov investigated the products of Ag spallation under bombardment by \(\alpha\)-particles with an energy of 550 MeV, deuterons of 280 MeV, and protons of 480 MeV. The emission of light nuclei \(\mathrm{C}^{11}\), \(\mathrm{Na}^{24}\), \(\mathrm{P}^{33}\), \(\mathrm{F}^{18}\), \(\mathrm{Be}^{7}\), \(\mathrm{Li}^{8}\), \(\mathrm{K}^{41}\), etc., was studied in detail. Possible mechanisms for the formation of the detected products are considered, and it is shown that their appearance may be regarded as the result of the successive development of two basic processes in a complex nucleus: an intranuclear cascade associated with the knocking out of fast particles, and the evaporation of nucleons from an excited nucleus.

Very interesting results, confirming the important conclusion on the existence of various mechanisms of the process of nuclear fission, were obtained in the work of N. A. Perfilov, N. S. Ivanova, O. V. Lozhkin, V. I. Ostroumov, and V. P. Shamov, “Fission Nuclear Reactions on \(\pi^{-}\)-Mesons and Fast Protons.” The recording of fission processes and the identification of the products formed were carried out by the method of thick-layer photographic plates. The substances studied (U, Bi, W) were introduced into the photographic layer either by soaking in aqueous solutions, or in the form of particles 3–5 \(\mu\) in size, insoluble during the subsequent treatment.

The mechanism of nuclear fission by slow \(\pi^{-}\)-mesons proved to be very similar to the mechanism of fission by fast nucleons: after capture into one of the Bohr orbits of the atom, a slow \(\pi^{-}\)-meson interacts with a pair of nucleons \((np)\) or \((pp)\), transferring to them the charge and energy connected with the rest mass. In this process two fast particles arise, with energies of the order of 70 MeV each, which collide with the nucleons of the nucleus and excite the nucleus, imparting to it an excitation energy of about 90 MeV. Thereafter fission proceeds as a process competing with nucleon evaporation. The authors note that some of the facts they discovered (for example, the increase in the number of asymmetric fissions with increasing excitation energy up to hundreds of electron-volts) are necessary for their explanation in the creation of a more complete and modern theory of atomic-nucleus fission.

In the report by G. M. Kukavadze, M. P. Anikina, L. L. Goldina, and B. V. Ershler, the results were presented of a mass-spectrometric analysis of Nd and Ce isotopes among the fission products of \(\mathrm{U}^{233}\), data on which have so far been few and inaccurate.

The action of radioactive radiation on various materials leads to a change in chemical properties, causes a restructuring of the molecular structure, inhibits some and accelerates other chemical processes.

In the report by V. L. Karpov, “The Effect of Nuclear Radiations on High-Polymer Substances,” it was shown that under the action of γ-radiation the molecules of polyethylene “cross-link” with one another, forming a very stable network, which leads to a sharp change in mechanical properties, solubility, etc. This process is analogous to the process of vulcanization of rubber and therefore has received the name “radiation vulcanization.” It proceeds very effectively: to produce cross-linking, the formation of a single “cross-linking” bond per molecule consisting of several thousand CH₂ units is sufficient. A detailed study of such processes may lead to the creation of high-polymer materials with entirely new service properties.

In the report by N. A. Bakh the influence of radiation on aqueous salt solutions was considered, and in the report by M. A. Proskurnina, V. D. Orekhov, and E. V. Barenko, on the course of oxidation–reduction reactions.

Radioactive and stable isotopes are a powerful tool for investigating the chemical structure and mechanism of chemical reactions. Without changing the mechanism by which a given process proceeds, they make it possible to judge it in considerably greater detail than do previously known analytical methods.

A survey of some possibilities of the isotope method was given in the detailed report by A. I. Brodskii, “Investigation of the Structure and Reactivity of Chemical Compounds by Means of Isotopes.” This same question, as applied to complex compounds, was analyzed in detail in the report by A. A. Grinberg, “Investigation of the Structure and Transformations of Complex Compounds by the Method of Labeled Atoms.” In the reports by G. P. Mikhailukhina and E. N. Guryanova, V. N. Vasil’eva and L. S. Kuzina, the use of labeled atoms for studying the mechanism of action of accelerators of the rubber-vulcanization process was considered; the role of these accelerators in the industrial production of rubber is very great.

An interesting communication on the use of organic coprecipitants in analytical chemistry was made by V. I. Kuznetsov. Organic coprecipitants, which have recently begun to be used, in particular, for extracting the products of nuclear reactions, possess substantial advantages over inorganic precipitants (high selectivity of action, ease of selection, wide range of choice). The report analyzed in detail various methods for the use of organic coprecipitants and indicated the prospects for their utilization.

A detailed analysis of the isotopic composition of natural lead and of its geochemical significance was made by A. P. Vinogradov.

S. T. Konobeevskii spoke about the phase diagrams of certain systems obtained on the basis of plutonium (Pu—Be, Pu—Pb, Pu—V, Pu—Cr, Pu—Fe, etc.).

Of the 20 reports heard at the sessions of the Department of Biological Sciences, half were devoted to analysis of the action of radiation on various biological structures (proteins, the nervous system, plants and animal organisms); the other half was connected with work on the use of labeled atoms for the analysis of physiological and biochemical processes.

In the report by L. A. Orbeli, “The Effect of Ionizing Radiations on the Animal Organism,” a number of general as well as methodological questions connected with the study of the influence of radiations on living organisms were considered.

The influence of ionizing radiations on the fertility of mice and the viability of their offspring was described in the report by N. I. Nuzhdin, N. I. Shapiro, O. N. Petrova, and O. N. Kitaeva. A detailed study of the sterilizing action of X-rays showed the presence of a clearly expressed sterilization effect that is transmitted by heredity.

In the report by E. Ya. Graevskii, work on protecting the animal organism from the damaging action of ionizing radiations was analyzed. In particular detail, the report considered the protective

action of carbon dioxide and bone-marrow emulsion. The data obtained are of undoubted practical interest.

A number of interesting data were contained in the report by P. F. Minaev, “On the local action of X-rays on various parts of the central nervous system of animals.” One of the conclusions of the report is the confirmation that the central nervous system, along with a high sensitivity to penetrating radiation, also possesses a high resistance to its effects.

In the report by A. M. Kuzin, “Biochemical foundations of the biological action of ionizing radiation,” the primary biochemical reactions occurring in the organism under the action of penetrating radiation were elucidated.

A. G. Pasynskii reported on studies of the effect of ionizing radiation on proteins and protein complexes.

A detailed analysis of the fate of various microorganisms in the course of cold, or “radiation,” sterilization of food products, pharmaceutical preparations, and surgical accessories was carried out in the report by M. N. Meisel, T. S. Remezova, R. D. Gal’tsova, G. A. Medvedeva, N. A. Pomoshnikova, M. N. Shal’nova, and V. A. Alekseeva. Irradiated microorganisms die not at once, but remain alive for some time and continue to carry out a number of biochemical processes. The damage received by microbes leads to their death only after some time. Microbes have structures, functions, and biochemical systems that are more or less resistant to radiation.

In the report by P. A. Vlasov and N. G. Zhezhelya it was shown that under the influence of small doses of radioactive irradiation, seeds of agricultural plants make fuller use of nutrients and exhibit an intensification of metabolism, which ultimately leads to an increase in crop yield and plant productivity.

Among the studies carried out with the aid of labeled atoms, the work of N. M. Sisakyan, “Application of C¹⁴ and P³² in the study of the synthetic functions of isolated chloroplasts,” is of greatest interest. Investigating, with the aid of radioactive carbon and phosphorus, the synthetic functions of chloroplasts, the author showed that, in addition to assimilating carbon dioxide from the air, they are capable of synthesizing and oxidizing fatty acids, and also of participating in protein synthesis.

In two reports—by E. A. Boichenko and N. I. Zakharova, “Application of C¹⁴ in the study of the primary products of photosynthesis,” and by O. V. Zalenskii, “On the distribution of carbon among organic substances formed with the participation of photosynthesis”—the latest achievements obtained thanks to isotope methods in such an important field of research as the problem of photosynthesis were elucidated. In particular, it was possible to identify the substance that is the primary acceptor of carbon dioxide and to show that assimilation of carbon dioxide begins with its addition to the iron of the acceptor molecule. It was also shown that the role of photosynthesis in the formation of organic substances differs in different plants, and also under different conditions of physiological activity.

I. M. Polyakov reported on highly interesting studies on the use of radioactive isotopes S³⁵ and P³² in studying the fertilization of plants.

Radioactive atoms make it possible to study in detail the processes by which living organisms assimilate nutrient substances, making it possible to find the most effective methods of fertilizing plants and feeding animals. Two reports at the session were devoted to this important problem—the report by F. V. Turchin, M. A. Guminskaya, and E. G. Plyshevskaya, “Study of nitrogen nutrition and metabolism of plants using the isotope N¹⁵,” and the report by B. N. Stepanenko, “Study of carbohydrate metabolism in the animal organism with the aid of radioactive carbon.”

In the report by Kh. S. Koshtoyants, T. M. Turpaeva, and D. E. Ryvkina, extremely interesting studies were described in detail on the biochemical basis of the processes of nervous excitation and inhibition with the aid of the radioactive isotopes Hg²⁰³ and P³². The nature of nervous excitation and inhibition is one of the most pressing problems of contemporary physiology and medicine. The participation in these processes of special chemically active substances, the so-called “mediators” of nervous excitation, has been established. The influence of the reactive groups of protein bodies and, in particular, their sulfhydryl groups on the development of processes in the nervous system was the subject of research by Kh. S. Koshtoyants. The data obtained expand our understanding of the mechanism of action of the nervous system.

At the meetings of the Division of Technical Sciences, 18 reports were presented.

In the report by A. M. Samarin and E. S. Kalinnikov, the study of the sources of contamination of steel by nonmetallic impurities, which sharply reduce its strength, wear resistance, corrosion resistance, and other properties, was described. With the aid of the radioactive isotope Ca⁴⁵, introduced into various refractory materials, the authors traced the influence of the refractory lining materials of casting ladles and troughs on contamination of ball-bearing steel. The results obtained make it possible to select optimal casting conditions that reduce the amount of nonmetallic impurities.

A. I. Osipov, L. A. Shvartsman, V. E. Iudin, and M. L. Sazonov used the isotope Co⁶⁰ to study the processes of mixing metal and slag in the bath of a 350-t open-hearth furnace at the Azovstal plant. The data obtained indicate the presence in the bath of counteractive convective flows with velocities up to 100 m/hour. A quantitative relationship was found between the rate of carbon oxidation and the values of the coefficients of turbulent diffusion, and other valuable results were obtained.

O. B. Travin and L. A. Shvartsman applied the isotope S³⁵ to a detailed study of the process of sulfur transfer from cast iron into slag. It was established, in particular, that the Si and Mn present in cast iron not only do not slow the desulfurization process, but under certain conditions can accelerate it.

Radioactive atoms are a remarkable means for studying the processes of diffusion and evaporation of various substances. The application of this method to determining the rate of evaporation and the diffusion coefficient in metals was the subject of reports at the session by A. N. Nesmeyanov, N. F. Lebedeva, V. I. Logacheva, and E. G. Chudinov. In the report by A. A. Zhukhovitskii, various methods for studying diffusion in metals were analyzed, and a number of experimentally verified methods were proposed—the “thin-layer method,” the “thick-layer method,” and the “imprint method”—whose accuracy is 5–10%.

The use of radioactive isotopes shortens the time required and greatly simplifies the procedure for studying the friction of various surfaces, selecting lubricating materials, and determining the wear resistance of machine parts. These problems were touched upon in the report by Yu. S. Zaslavskii, “Investigation of the Wear Properties of Oils and Fuels with the Aid of Radioactive Isotopes,” and in the report by E. P. Nadeinskaya, “Investigation of Wear of a Cutting Tool with the Aid of Radioactive Isotopes.” In the first work, the studies were carried out on single-cylinder carburetor four-stroke engines with a power of 3 h.p. at 2200 rpm, in which the upper piston compression ring contained either Fe⁵⁹ or Zn⁶⁵. Oils AS-5, AS-5 with 3% NAKS additive, SU, and SU with 2% additive “A” were investigated. To study the mechanism of action of anticorrosive additives, the isotopes S³⁵ and P³² were used. In the second work, the radioactive isotope W¹⁸⁷ was used. The data obtained are of great practical value and are important from the methodological standpoint.

Creation of stable counters for recording γ-radiation (scintillation, self-quenching, etc.) made it possible, in the γ-defectoscopy method, to replace X-ray film, which greatly reduces the duration of exposure, makes it possible to monitor moving objects, and eliminates the large expenditure of costly film. It is enough to point out, for example, that a counter detects such weak γ-radiation that, to be recorded on film, would have had to act continuously for two years. The design of a cobalt γ-defectoscope for inspecting products up to 300 mm thick and its operation under factory conditions were discussed in the report by I. G. Fakidov and A. A. Samokhvalov, “Ionization Methods in γ-Defectoscopy of Metals of Great Thickness.”

In the report by A. M. Bogachev, B. I. Verkhovskii, and A. N. Makarov, new types of radioactive thickness gauges were described—devices for contactless determination of the thickness and density of materials—created by the joint efforts of the Laboratory of Isotopes and Radiations of the P. N. Lebedev Physical Institute of the Academy of Sciences of the USSR and the Central Automation Laboratory of the Ministry of Ferrous Metallurgy of the USSR. The industrial installations developed for measurements in the ranges 0.005–0.150 mm, 0.05–1.0 mm, and 2–10 mm were used successfully for two years at the rolling mills of the Magnitogorsk Metallurgical Combine named after Stalin, the steel-rolling and wire-rope plant named after Molotov in Leningrad, and the Sinara New Pipe Plant. An installation for measuring the thickness of tin coating successfully serves the hot-tinning unit at the Zaporizhstal plant.

M. A. Styrikovich reported on a large cycle of work studying the carryover of salts with steam in steam boilers and the hydrodynamics of two-phase liquids with the aid of the radioactive isotopes S³⁵, P³³, Ca⁴⁵, Co⁶⁰, and others. These works have great practical significance for all steam-power installations, making it possible to find ways of combating contamination of steam-turbine blades, overheating of steam lines, and other harmful effects.

In conclusion, a number of reports were heard devoted to the application of radioactive methods in prospecting for mineral resources.

In the report by V. N. Dakhnov, a detailed review was given of the various methods of radioactive prospecting used in our country, and further possibilities were indicated for the use of these methods in the search for B, Cd, Mn, Co, Hg, W, and other materials.

F. A. Alekseev, A. P. Grumbkov, and Yu. E. Kirshfeldt reported on the use of radiometric methods for searching for oil deposits in the report “On the Question of the Possibility of Using Radiometric Methods for Searching for Oil Deposits”; A. I. Kholin, in the report “Separation of Oil-Bearing and Water-Bearing Beds in Cased Wells by Radioactive Methods of Investigation”; N. K. Kukharenko, V. P. Odinkov, and Yu. S. Shimelevich, in the report “Possibilities of Using the Sodium-Activation Method for Detecting Oil-Bearing and Water-Bearing Beds and Determining the Oil-Water Contact in a Cased Well Column.” The report by G. N. Flerov and F. A. Alekseev was devoted to the same topic; in it were analyzed the possibilities for further improvement of the radiometric methods employed (the creation of small-sized accelerating tubes for increasing the power of the neutron flux, the use of tritium for monitoring the movement of formation waters and C¹⁴ for monitoring the movement of oil, etc.).

In the report by B. G. Erozaimskii and L. F. Bespalov, improved apparatus was described for radiometric investigations in the petroleum industry. The basis of the improvement is the replacement of discharge counters by scintillation counters.

The participants in the session familiarized themselves with a powerful synchrotron and with one of the atomic boilers of the Academy of Sciences of the USSR. They also made an excursion to the Atomic

the atomic power station of the Academy of Sciences of the USSR and viewed the film The First in the World about its operation.

The first session of the Academy of Sciences of the USSR devoted to the peaceful uses of atomic energy, together with the materials presented by our scientists at the conference in Geneva, convincingly demonstrated the enormous scope of the work being carried out in this direction in the Soviet Union. The proceedings of this session, published as a separate five-volume edition, constitute a significant contribution to the cause of mastering atomic energy for the benefit of all mankind.

V. A. Leshkovtsev