DMITRY VLADIMIROVICH
SKOBELTSYN

DMITRY VLADIMIROVICH SKOBELTSYN

(On the sixtieth anniversary of his birth)

On November 24, 1952, sixty years had passed since the birth of Academician Dmitry Vladimirovich Skobeltsyn, one of the greatest scientists of our country.

For about thirty years D. V. Skobeltsyn has worked in the field of the physics of the atomic nucleus and cosmic rays. In 1923 he began work on studying the mechanism of interaction of hard gamma rays with matter by means of a Wilson chamber.

These works were among the first investigations in the field of nuclear physics in the Soviet Union.

The beginning of these works dates to a time when the question of the quantum nature of radiant energy was highly topical. In 1923, ideas about “atoms of light” were applied by Debye and Compton to the question of the mechanism of scattering of electromagnetic radiation of very short wavelength. The quantum nature of light scattering could be established by detecting and studying recoil electrons. This was done with complete clarity in the experiments of Dmitry Vladimirovich Skobeltsyn, in which recoil electrons from the hard gamma rays of radium were observed in a Wilson chamber.

Especially fruitful was the method introduced by D. V. Skobeltsyn for observing the tracks of fast charged particles in a Wilson chamber placed in a magnetic field. This method made it possible, from the curvature of the tracks, to measure the energy of recoil electrons and thereby made possible a more detailed quantitative investigation of the Compton effect for gamma rays. The results obtained by D. V. Skobeltsyn led to the development of a new method of gamma-ray spectroscopy. In particular, they proved very important for establishing the dependence of the photoelectric absorption of gamma rays on wavelength.

In 1928 D. V. Skobeltsyn carried out a careful study of the angular distribution of recoil electrons, which showed the inadequacy of the Dirac–Gordon formula and at the same time for the first time directly confirmed the Klein–Nishina–Tamm formula,

derived on the basis of the Dirac equation. In addition to the fundamental significance of this result, by which the question of the basic equation of relativistic quantum mechanics was resolved, the confirmation of the Klein–Nishina–Tamm formula provided a reliable basis for the above-mentioned method of gamma-ray spectroscopy. The Wilson chamber method with a magnetic field, developed by D. V. Skobeltsyn, became one of the principal methods of investigation in the physics of the atomic nucleus and of cosmic rays. This method subsequently led to a large number of important discoveries in the field of the atomic nucleus and cosmic rays.

In 1927–1929 D. V. Skobeltsyn made another important discovery. He was the first to succeed in photographing, in a Wilson chamber, the tracks of charged particles of cosmic rays and in establishing a number of their properties. He showed that these particles possess a unit charge and have enormous energy.

At the same time D. V. Skobeltsyn established the simultaneous entry into the Wilson chamber of several particles of cosmic rays. The study of this phenomenon led D. V. Skobeltsyn to the conclusion that there exists some new mechanism of interaction of high-energy radiation with the atoms of the absorbing medium, one not fitting within the framework of the ideas accepted at that time. Soon afterward, Blackett and Occhialini, using a new ingenious method of photographing cosmic-ray tracks in a Wilson chamber, were able to observe this phenomenon on a larger scale, obtaining striking pictures of the so-called “showers” of cosmic rays.

In subsequent years and at the present time D. V. Skobeltsyn has directed a broad range of research on the study of cosmic radiation. These works have established that the determining processes in the interaction of cosmic radiation with matter are nuclear processes, and not electromagnetic ones, as had earlier been supposed.

D. V. Skobeltsyn took a special interest in studies of the so-called extensive atmospheric showers, which arise when primary particles of cosmic rays, possessing ultrahigh energies, enter the Earth’s atmosphere. Previously it had seemed established that the process of development of atmospheric showers was wholly determined by well-studied phenomena, the theory of which is given by quantum electrodynamics. However, the works carried out under the direction of D. V. Skobeltsyn showed the erroneousness of the former point of view and culminated in the discovery of the nuclear-cascade process. The above-mentioned works of D. V. Skobeltsyn and his pupils on the nuclear interactions of high-energy particles with matter were awarded the Stalin Prize, First Class, in 1951.

All the works conducted by Dmitrii Vladimirovich are characterized by breadth and principledness, as well as by a rare combination of theory and experiment.

In addition to his scientific work, D. V. Skobeltsyn devotes much time to scientific-organizational and pedagogical activity. As director he heads a large staff of scientific workers at the P. N. Lebedev Physical Institute of the Academy of Sciences of the USSR, having succeeded in this post the remarkable Russian physicist Academician S. I. Vavilov. D. V. Skobeltsyn’s activity in the training of young physicist specialists at the M. V. Lomonosov Moscow State University is also broad in scope. With Dmitry Vladimirovich’s direct participation, a large number of physicists have been trained who are now actively working in the most diverse fields of knowledge.

The lectures delivered by Dmitry Vladimirovich at Moscow University and earlier at the Leningrad Polytechnic Institute, as well as his talks at conferences and numerous seminars, are distinguished by their depth and novelty of presentation.

Dmitry Vladimirovich also takes a broad part in the public and state life of our country. He is chairman of the Committee for the International Stalin Prizes “For Strengthening Peace Among Peoples,” carrying out in this post extensive work to spread among progressive mankind the ideas of the great Stalin on the struggle for peace.

Dmitry Vladimirovich is also a deputy of the Supreme Soviet of the RSFSR, actively fulfilling the functions of a people’s representative entrusted to him by the voters.

D. V. Skobeltsyn’s varied activity has been repeatedly recognized by our country. In 1952 Dmitry Vladimirovich was awarded the newly established medal named after Academician S. I. Vavilov. The Soviet government has many times recognized Dmitry Vladimirovich’s services to the Motherland, awarding him the Order of Lenin and two Orders of the Red Banner of Labor.

We wish Dmitry Vladimirovich many long years of health and strength, so that he may continue to carry out his work for the benefit of our Motherland as successfully and fruitfully as before.