Bibliography

H. PETTERSSON und G. KIRSCH. Atomzertrümmerung. Verwandlung der Elemente durch Bestrahlung mit α-Teilchen. Pp. VIII + 247. Akademische Verlagsgesellschaft, Leipzig 1926.

Peterson and Kirsch. Destruction of Atoms.

It is already more than seven years since Rutherford’s first successful experiments on the artificial transmutation of elements were published. In our time, when the pace of development in physics has become quite dizzying, when entire fields grow up within a few months, one might have expected that over so long a period as seven years an enormous literature would have accumulated. Meanwhile, in actual fact, the number of works devoted to the artificial destruction of elements barely reaches three or four dozen, and, in essence, one may quite rightly say that on the whole globe there are only two places where these investigations are being carried out with any degree of systematic regularity. These two places are Rutherford’s Cavendish Laboratory in Cambridge and the laboratory of the authors of the book under review at the Vienna Radium Institute. Such slowness in the development and elaboration of one of the most important problems of modern physics is, of course, due to the great experimental difficulties that must be overcome in work in this field. The authors consider that the task of the book under review is to facilitate the work of investigators by giving a detailed description of the experimental technique, chiefly of those methods that have been developed at the Vienna Radium Institute.

The principal results obtained in both laboratories may be summarized as follows: 1. The reality of the phenomenon first observed by Rutherford in the “bombardment” of nitrogen atoms by fast α-particles has been proved beyond any doubt. 2. Likewise beyond any doubt the nature of the products of destruction has been established, or, more precisely, it has been proved that in destruction it is precisely hydrogen nuclei that are emitted. In this respect the experiments of the authors’ collaborator, G. Stetter, are especially clear and convincing; he succeeded in constructing a special “mass spectroscope” for H-particles, analogous to Aston’s “mass spectrograph.” 3. A method of observation has been developed—especially high-aperture optics, methods for preparing especially sensitive scintillating screens have been devised and used, as have arrangements for photographing (!) scintillations. 4. Methods have been developed for observing the products of destruction emitted at right angles to the direction of the stream of α-particles and “retrograde” particles, i.e., particles emitted at an angle of 180°. Both methods, developed quite independently in Cambridge and in Vienna, have considerably expanded the possibilities of observation, since they make it possible to detect also such products of disintegration whose range is less than the range of the incident α-particles. 5. A long series of elements has been investigated, and it has been established in which of them α-particles cause disintegration of the nucleus. 6. A long series of works has been devoted to establishing the nature of the particles of long range emitted by radium C and thorium C. 7. Finally, especially in the Cambridge laboratory, detailed study is being made of

scattering of α-particles by heavy and light elements is one of the few methods for studying the structure of the nucleus and the laws of the forces acting in its immediate vicinity. In particular, Bieler’s experiments (1924) and the later experiments of Rutherford and Chadwick (1925) showed that, in the scattering of fast α-particles by light atoms, considerable deviations from the simple Coulomb law of interaction are observed. Bieler could interpret his results only by assuming that, at a certain distance, an attractive force, inversely proportional to the fourth power of the distance, is added to the repulsive force acting between the nucleus and the α-particle. Peterson indicated that the occurrence of this additional force can be explained without abandoning the elementary Coulomb law, by assuming that at close range a polarization of the nucleus by the strong field of the α-particle is revealed. Proceeding from the same assumption, Debye (Phys. Zs. 1926) was able satisfactorily to interpret the anomalies observed by Rutherford and Chadwick.

The book under review has the following contents: I. Preliminary history of the problem. II. Investigations (α-rays, H-rays). III. Destruction of atoms. IV. New investigations on collisions of nuclei. V. Properties of H-rays. VI. The question of regulating radioactive processes. VII. Theoretical considerations. VIII. Methodology. IX. Index of the literature. The book gives a complete picture of the present state of the question. It goes without saying that the authors dwell with particular fullness on the work of their own laboratory, although the Cambridge work is also given the attention corresponding to its exceptional importance. On a whole series of questions there still remain substantial disagreements between the two laboratories; such are the question of α-particles of abnormally long range (pp. 72–83), and also the question of the disintegration of the carbon nucleus and of certain other elements. These disagreements are not surprising, since the matter almost always concerns observations of exceptional difficulty.

Physicists interested in this field will undoubtedly be very grateful to the authors for compiling this interesting and complete survey. The numerous and detailed indications concerning experimental technique will be of great service to investigators working also in adjacent fields.

E. Shpolsky.