P. N. Lebedev Physical Institute of the USSR Academy of Sciences

D. V. Skobeltsyn and I. M. Frank

Introduction

The P. N. Lebedev Physical Institute of the USSR Academy of Sciences traces its origin to the oldest center of research in experimental physics in our country.

In 1725, simultaneously with the Academy of Sciences, its Physical Cabinet was founded; it existed for almost two centuries and in 1912 was reorganized into a physical laboratory. Already after the Great October Revolution, in 1921, the laboratory was transformed into the physics division of the Physico-Mathematical Institute of the Academy. From the end of 1932 this division was headed by S. I. Vavilov. In the summer of 1934, by decision of the government, the Institute, together with the Academy of Sciences of the USSR, was transferred from Leningrad to Moscow. At the same time the physics division was separated into an independent institute and received its present name.

Thus, in 1934 the physical laboratory (division) of the Academy was transformed into the P. N. Lebedev Physical Institute (FIAN), with the organizational structure that, to a certain extent, has been preserved to the present day.

The first director of the Institute, who headed it from 1934 to 1951, was S. I. Vavilov.

After the death of S. I. Vavilov, D. V. Skobeltsyn was elected director of the Institute.

The prehistory of the prerevolutionary period (as well as the postrevolutionary period of the history of FIAN up to 1945) is set forth in S. I. Vavilov’s book The Physical Cabinet—Physical Laboratory—Physical Institute of the USSR Academy of Sciences over 220 Years*.^1

Already during the brief Leningrad period in the history of FIAN, a group of young physicists formed by S. I. Vavilov carried out a number of works whose significance became fully clear only later and which influenced the entire subsequent development of the Institute.

Special mention should be made of the work, carried out under the direct supervision of S. I. Vavilov, on the study of the luminescence of solutions of uranium salts. This work, as is known, led to the discovery

* The beginning of the history, as already indicated, goes back to the first decades of the eighteenth century and to the scientific activity of many outstanding scholars that took place in the “Physical Cabinet” of the Academy (M. V. Lomonosov, L. Euler, D. Bernoulli, V. V. Petrov, E. H. Lenz, B. S. Jacobi, G. I. Wild, and others), and later in its “Physical Laboratory” (B. V. Golitsyn, P. P. Lazarev).

of the Vavilov–Cherenkov effect. One should also mention work on the study of electrical breakdown in gases² and the beginning of work in nuclear physics.

Among S. I. Vavilov’s young collaborators of that time, who subsequently became leading workers of the Physical Institute of the Academy of Sciences, one may name B. M. Vul, L. V. Groshev, N. A. Dobrotin, I. M. Frank, and P. A. Cherenkov.

Under the direction of S. I. Vavilov, the P. N. Lebedev Physical Institute of the Academy of Sciences of the USSR was created and grew; it immediately became a leading scientific center in Moscow and in the country. Outstanding physicists, who by that time had already created major schools of their own, were drawn into it.

From this time on, L. I. Mandelstam and N. D. Papaleksi, as well as L. I. Mandelstam’s closest collaborators—G. S. Landsberg and I. E. Tamm—concentrated their scientific activity mainly at the Physical Institute of the Academy of Sciences. Students of younger generations also came with them. Among the latter were M. A. Leontovich, as well as M. A. Levitkovsky, S. M. Rytov, M. I. Filippov, and, later, S. E. Khaikin*).

A laboratory of oscillations was created (at present named after L. I. Mandelstam and N. D. Papaleksi), which at that time concentrated its research in two principal directions—the problems of the propagation of electromagnetic waves and the problems of nonlinear oscillations.

Under the leadership of G. S. Landsberg, the laboratory of physical optics began its research activity; its subject matter, in the field of problems of light scattering and its applications to molecular analysis and the study of the structure of liquids, produced varied results and developed successfully, preserving its basic orientation up to the present time.

Together with the laboratory of spectral analysis, formed later and directed by S. L. Mandelstam, there arose a leading research center of all-Union importance in the field of optics and spectral analysis.

New forces joined the luminescence laboratory headed by S. I. Vavilov: V. L. Levshin, M. A. Konstantinova, L. A. Tumerman, and V. V. Antonov-Romanovsky continued (or began) their fruitful research activity there.

The main direction of their work at that time was the investigation of the nature of crystalline phosphors and their applications, molecular luminescence, and luminescence analysis.

The luminescence laboratory, whose subject matter later expanded considerably, also became a leading and unifying all-Union center of research work in this field of physics.

Under the leadership of I. E. Tamm, a Theoretical Department was created and developed successfully; it worked on a wide range of problems in theoretical physics, and in particular on the theory of the atomic nucleus and cosmic rays. This department soon acquired leading importance not only within the Institute, but also beyond its limits.

Outstanding physicists took part in the work of the department at various times. Among them were V. A. Fock, D. I. Blokhintsev, S. Z. Belenky, K. V. Nikolsky, and Yu. B. Rumer. A. D. Sakharov began his scientific work as a graduate student in the theoretical department.

*) For several years A. A. Andronov and G. S. Gorelik also worked at the Physical Institute of the Academy of Sciences.

Among the staff members of the Theoretical Department who began their activity in it if not from the moment of its formation, then in the very first years of its existence, and who are now its leading workers, one may name V. L. Ginzburg, M. A. Markov, and E. L. Feinberg.

At FIAN an acoustics laboratory was organized, at first under the direction of S. N. Rzhevkin, and then, from 1940, of N. N. Andreev. Later its staff included L. M. Brekhovskikh, L. D. Rozenberg, and Yu. M. Sukharevskii.

In 1954 this laboratory was separated into an independent Acoustics Institute of the Academy of Sciences of the USSR.

Alongside the laboratories listed above, at the head of which, from the very beginning, stood major scientists who had already made their way in science, the young groups created by S. I. Vavilov also developed and strengthened successfully. A small nuclear laboratory began its work. The group of physicists working in it was soon joined by V. I. Veksler and S. N. Vernov.

We shall speak below about the postwar development of this group, which has outstanding achievements and has grown to the size of four laboratories, comprising about half of FIAN in its present composition.

The laboratory of dielectric physics, headed by B. M. Vul, also continued its work successfully. This “cell,” which had arisen back in the Leningrad period of FIAN, subsequently grew into a strong collective, which also plays a leading role in this field and has discoveries of great significance to its credit.

The Institute lived through the difficult years of the Great Patriotic War in Kazan, contributing its share in strenuous work to the cause of helping the army and the defense industry of our country.

Many staff members—and, first of all, the younger generation of research workers and graduate students, as well as the numerous students of Moscow University assigned to the Institute—volunteered for the Soviet Army and the people’s militia. Talented research workers of the Institute’s oscillations laboratory who voluntarily went to the front gave their lives on the fronts of the Patriotic War: M. A. Divils’kovskii and M. I. Filippov, and the graduate student M. L. Kotlyarevskii. The collective of the Institute will always honor the bright memory of comrades who fell in the struggle against fascism.

S. I. Vavilov concluded his small book mentioned above, written in the historic days of the final victory over fascism, with the words*:

“These days will in many respects determine the future development of all mankind. Together with the entire Soviet people, we hope to become participants in a new, as yet unseen rise of socialist construction and cultural flourishing of our Motherland. Just as in the years of war, in the years of peace physicists are ready to apply their knowledge, skill, and patriotism for the benefit of their native people and of all mankind.”

The collective of the Physical Institute is happy that it has indeed become an active participant in this unprecedented growth and rise of our science and culture, in which the development of physics has played a very important role. Now, in the days of the fortieth anniversary of the Great October Revolution, as in former years, the collective of the Institute’s workers is making every effort to solve with honor the numerous and responsible tasks that our Socialist Motherland sets before us.

* See ¹, p. 70.

Since the time when S. I. Vavilov completed his survey, 12 years have passed, and on the eve of the 40th anniversary of October we are once again summing up the results of our work.

The changes that have taken place in the Institute are very great. In the postwar years our science and technology solved the grand problem of obtaining atomic energy. To one degree or another, all branches of the exact sciences and technology took part in solving the diverse tasks connected with this problem. However, first and foremost it required an entirely different scope and level of work in the field of nuclear physics and related disciplines. The Physical Institute of the Academy of Sciences did not stand aside from this.

The Institute took an active part in solving many scientific problems necessary for the development of a number of other branches of technology as well. In turn, the rapid progress of technology in our country could not fail to exert a decisive influence on the development of the Institute. The character of scientific work also changed in the sense that the scientific worker ceased to be a scholar working, in most cases, alone, sometimes with the help of a laboratory assistant or a skilled mechanic*). As a rule, scientific problems are now solved by a collective consisting of scientific workers, engineers, and technicians. In addition, for successful work extensive production workshops are necessary, capable of rapidly manufacturing complex experimental apparatus.

All this required considerable growth of the Institute. The number of employees of the Institute has increased since 1945 by more than 7 times. The large new building that the Institute received in 1951 has now already become cramped.

The composition of the staff has also changed substantially.

Over the past years our collective has suffered many grievous losses. In 1944 L. I. Mandelstam died—the founder of the laboratory of oscillations and the head of a large school of Moscow physicists; in 1947 N. D. Papaleksi, who headed the laboratory of oscillations, passed away. In 1951 S. I. Vavilov died—the founder and first director of our Institute. In 1957 we lost G. S. Landsberg—the head of the Institute’s optical laboratory (now the laboratory named after him).

At the same time the Institute was continually replenished with young people. A number of young scientists returned after demobilization from the Army. Many young people who had fought in the ranks of the Soviet Army began scientific work for the first time in the postwar years. It is precisely this generation of scientists, together with the small older generation, that has now become the principal driving force in science.

Of the total number of 20 doctors and 100 candidates of science now working at the Institute, the majority are alumni of the Institute who began their scientific work there.

In speaking of the Institute’s activity, one cannot fail to say a few words about its library. This is, undoubtedly, our oldest physics library.

The book and journal holdings of the library have been continuously replenished throughout all the years of its existence. As a result, it now possesses unique sets of scientific journals in physics over many years. Among the books there are rare books of the 16th, 17th, and 18th centuries. At present, under the experienced direction of G. O. Vreden-Kobetskaya, the library has collected about 200,000 volumes of books and journals. The library subscribes annually to about 500 titles of foreign and Soviet journals. It issues annually more than 90 thousand books and journals to its numerous readers, whose number has exceeded 2000. Extensive bibliographic work is being carried out.

*) Such assistants rendered invaluable help to scientists. One of them—A. M. Rogovtsev, who began his activity back under P. N. Lebedev, still works at the Institute.

GENERAL OVERVIEW OF THE SUBJECT MATTER AND SOME RESULTS OF THE INSTITUTE’S WORK

Before proceeding to a brief survey of the work of the individual laboratories of FIAN, it may be appropriate to characterize certain features of the development, over the last ten to twenty years, of its subject matter as a whole, in the light of the evolution that has marked this epoch in the history of world physics. At the same time, it is natural to single out certain most important achievements—“special points” in the overall result of the Institute’s work.

FIAN, as an independent “head” institute, was organized at the beginning of the thirties of our century. Its emergence thus coincided in time with the beginning of a new era in the development of the problems of the forefront of the newest physics. To this time belong the discovery of new elementary particles—the neutron, the positron, and then the meson. These discoveries led physics to key positions on the paths into an entirely new domain of phenomena of elementary-particle physics, all the originality of which has been revealed only in the very recent period.

Even then it became clear that, for successful progress along these new paths into the still unexplored regions of the microworld, it was necessary to bring in the corresponding powerful means, quite unusual for the physics of the preceding period, which could equip researchers with the technique for obtaining high-energy particles. At that time accelerators of charged particles, in particular cyclotrons, were already beginning to be introduced into physics; however, the range of their application was limited by certain energy bounds, still wholly insufficient, which made it impossible with their aid even to approach the energies of particles of cosmic radiation.

In 1944 V. I. Veksler, who at that time was directing a number of works on the study of cosmic rays, put forward ideas that formed the basis of the newest cyclic accelerators. V. I. Veksler’s discovery (and, somewhat later, that of McMillan in the USA) of the principle of autophasing made it possible to overcome the barrier established by nature for the acceleration of “heavy” particles—protons and deuterons—by the ordinary method: an electric field of constant frequency, owing to a peculiar “resonance” effect in the constant magnetic field of the cyclotron. Substantially limited on the side of high energies was also the field of application of the electronic accelerators then realized—the betatrons.

As a result of V. I. Veksler’s work, the possibility opened up of rapid upward movement along the energy scale. For this it was necessary to bring in extremely complex and bulky technical means and the cooperation, in their creation, of outstanding engineers of various specialties.

Thanks to the support of the Soviet Government, at FIAN, under the general direction of V. I. Veksler and on the basis of the principles discovered by him,3 the construction of a number of electron accelerators—synchrotrons—was carried out, leading in recent times to the construction (already outside FIAN, in the town of Dubna) of a unique ring proton accelerator (synchrophasotron), transferred to the Joint Institute for Nuclear Research. As is known, in April 1957 this accelerator produced particles with the record energy of about 10 billion electron-volts, i.e., with an energy of the order of the mean energy of primary cosmic rays—a thousand times greater than that which had been accessible for an ordinary cyclotron. The construction of the synchrophasotron in Dubna was preceded by the creation of a model (for 180 MeV protons), which was built, put into operation, and studied at FIAN.4 The introduction into physics of unique particle accelerators has had, as is known, a revolutionizing influence on the state of science in the field of elementary-particle physics.

The implementation of construction of accelerators of this kind had a very strong influence also on the development of FIAN. Laboratories with bulky industrial-type installations arose. A strong school was created for developing problems of accelerator technology. Beginning in 1949, using a new and highly complex technical base, work under the direction of V. I. Veksler has been carried out on the study of photonuclear interactions in various energy ranges.

Progress in developing problems of elementary-particle physics had been prepared by the study of cosmic-ray phenomena (c. r.).

A large cycle of work at FIAN, covering the period from the beginning of the Institute’s activity, led to a reconsideration and solution of the question of the nature of the predominant component of primary cosmic radiation and of the phenomena caused by it in the atmosphere.

In the postwar period the laboratory headed by N. A. Dobrotin has been conducting, on a broad front, observations of cosmic radiation in the stratosphere, at mountain altitudes, and at sea level.

All these successfully developing works have in recent times been directed toward a common goal—the elucidation of the mechanism of elementary nuclear interactions in the region of ultrahigh energies. This is a region of energies several orders of magnitude higher than the mean energy of primary cosmic rays, or even the energy that can be attained in any foreseeable future by means of accelerators.

Investigations carried out by the group of S. N. Vernov (in particular, in the equatorial expedition of 1949—N. L. Grigorov et al.)^5, which studied phenomena in the stratosphere, by the end of the 1940s had with certainty confirmed the hypothesis of the proton nature of the predominant component of primary c. r. This hypothesis, advanced by Schein in the USA, seemed to be in contradiction with what was known about the “soft component” of c. r. and especially about the nature of extensive air showers (Auger showers).

At the same time, observations made in the Pamirs (in 1945–1946) led to the discovery of a new phenomenon, subsequently studied in detail, of special mixed showers, called by the authors of these works “electron–nuclear showers.”^6 Thereby a mechanism was uncovered which represents the initial link in the chain of c. r. phenomena developing in the atmosphere; this made it possible to remove the above-mentioned contradiction by connecting the picture of these phenomena with the proton, or nuclear, nature of the primary radiation, which generates “electron–nuclear” showers in the upper layers of the stratosphere.

What had previously been regarded as the main essence of the phenomenon of extensive air showers—electromagnetic cascade processes—actually proved to characterize only its external aspect. As was established, at the basis of c. r. phenomena and, in particular, of atmospheric showers lie nuclear interactions in the high-energy region of such particles as protons, mesons, etc., and a distinctive nuclear-cascade process (G. T. Zatsepin).^7 The picture constructed as a result of many years’ work by a large collective^8 now permits certain conclusions to be drawn about the mechanism of elementary nuclear interactions in the energy region exceeding \(10^{11}\)—\(10^{13}\) eV. Thus, for example, the lower limit of the effective interaction cross section, the characteristic of the angular distribution of particles in their multiple production in elementary acts of nuclear collisions, and the “degree of inelasticity” of collisions have been indicated.^9

Thus, firmly grounded experimental positions have been created for the critical consideration of models of the mechanism of multiple-

...of particle production (in particular such as those proposed by Fermi and Landau). The results of experimental investigations also suggest certain new hypotheses and ideas for interpreting such models.

Recently, investigations by the photographic-emulsion method, aimed at solving the same problems, have also been carried out successfully.

The problems of elementary-particle physics and nuclear interactions were also the main subject of the work of the Institute’s theoretical department (especially in the postwar period).

The works of I. E. Tamm on the theory of exchange nuclear forces are widely known.

The task of constructing a quantum theory applicable to questions of the physics of meson interactions led I. E. Tamm to formulate the fundamental principles of an approximate method, now widely cited in the world literature as the Tamm—Dancoff method.^10

A series of works by I. E. Tamm and S. Z. Belen’kii, as well as by S. Z. Belen’kii and his students, on the theory of cascade processes in cosmic rays^11 (and, more recently, on the theory of multiple particle production in high-energy nuclear collisions) constitutes a substantial contribution to world science.

One may note one feature characteristic of the physics of our time in general, which could not fail to manifest itself in the postwar years in the general direction of the research program of such a many-sided institute as FIAN. This feature is the complexity of many particularly urgent problems, which touch in one way or another upon different, sometimes quite remote, fields of science, and whose solution requires the coordinated efforts of specialists of various profiles.

An example of such an interrelation of different aspects of phenomena—in the present case we have in mind optics, on the one hand, and nuclear physics, on the other—may be the discovery of the remarkable effect that is one of the Institute’s most outstanding achievements. We have in mind the Vavilov—Cherenkov effect, which has already been mentioned.^12

The history of the discovery of the phenomenon itself, and then (two decades later) of its applications, is highly noteworthy.

As is well known, it is a matter of the radiation of a charged particle in interaction with a medium in which it moves uniformly with a velocity exceeding the phase velocity of light in that medium.

We have already mentioned the work of the Leningrad period in the history of FIAN that led to this discovery, whose significance was not understood at once, and which was made as the result of studying phenomena that seemed to be of interest only to specialists concerned with a narrow range of problems of luminescence.

The nature of the phenomenon was revealed only several years later by I. E. Tamm and I. M. Frank.^13 This proved possible as a result of the combination of ideas and methods for interpreting phenomena characteristic, on the one hand, of optics and, on the other, of nuclear physics.

By the work of Tamm—Frank and by many subsequent works, the fundamental and very broad significance of the phenomenon was revealed in all its fullness, both in its optical aspect and from the point of view of the problems of the physics of “radioactive”—nuclear—radiations. It also became clear that this phenomenon had often been observed earlier as well, but had not been identified as a special one, and that the theoretical scheme for its interpretation could have been found in some works of earlier times (Lord Kelvin, Sommerfeld). However, only about 20 years after the discovery of the effect did its practical value for experimental nuclear physics become fully clear.

In recent years, close to our own time, the newest technical means of amplifying photocurrents have made it possible to use the Vavilov–Cherenkov effect to solve one of the fundamental problems in the study of elementary particles investigated with modern accelerators. At present, so-called Cherenkov counters have become widely used; they make it possible, from the radiation in the corresponding medium, to determine the velocity of a particle accelerated in an accelerator to moderately relativistic speeds. By this method the particle’s velocity can be determined independently of its mass, which in appropriate cases makes it possible to obtain an additional independent parameter necessary for identifying the particle. The use of this feature played a substantial role, for example, in the experiments that led to the discovery of the antiproton.

Ultrarelativistic particles, whose clusters form the so-called “wide” atmospheric showers of cosmic rays, can be detected from flashes of light caused by Vavilov–Cherenkov radiation even in a gas—atmospheric air—which opens new possibilities for studying them.

Work in this direction is still unique. At the Lebedev Physical Institute, observations of this kind were carried out by A. E. Chudakov. He also proposed the ideas of a method which will probably make it possible to use Vavilov–Cherenkov radiation to realize a kind of energy “integrator” for determining the total energy carried by shower streams of many particles, which may prove very important for solving experimental problems in the physics of particles of “superhigh” energies.

In the work of the Lebedev Physical Institute one can cite many other examples of similar problems of a complex character. We shall return to this later.

In surveying the development of individual laboratories of the Lebedev Physical Institute, one cannot fail to note (at least by the example of some of them) another feature as well, one characteristic of the physics of our time. This feature is the close interconnection with technology—or, better said, the interdependence of science and technology. It is appropriate to emphasize the two-sided character of this interconnection or interdependence.

The history of the work of the Oscillations Laboratory of the Lebedev Physical Institute, which has great achievements to its credit, may probably serve as a vivid example of such a combination of elements of technology and physics, connected with their mutual penetration and fertilization.

On the basis of the very rich classical heritage left by the founders of the laboratory—L. I. Mandelstam and N. D. Papaleksi—and of the scientific traditions they created, the laboratory was able, during the last few years, to reorganize its subject matter, developing new directions in its work and making a substantially new contribution to the history of our science.

One of these directions—radio astronomy—arose historically as a result of the consistent development of a set of problems that had occupied a significant place among the questions worked on by the laboratory even in the prewar period of its existence, namely problems of radio-wave propagation.

In the postwar period the newest technical means made it possible to approach these problems using new and distinctive cosmic sources of radio emission, namely, above all, the radio emission of the Sun. Work in this direction, begun on the initiative and under the direction of N. D. Papaleksi, from 1948 continued under the direction of S. E. Khaikin^14, and then, from 1953, of V. V. Vitkevich; moreover, in its further development it was for the most part ...

purely radio-astronomical orientation. Thus there arose at FIAN, for the first time in the USSR, a new group of radio astronomers, devoting its investigations to the study of cosmic objects from the standpoint of the radiophysical processes occurring in them.

Somewhat more will be said about these works below.

On the basis of the old oscillations laboratory of FIAN, A. M. Prokhorov created a young collective developing another major complex problem—radio spectroscopy, in which the physics of quanta and radio engineering are combined in a highly distinctive way.

A major achievement is the work based on an idea put forward as early as 1954–1955. We have in mind the so-called molecular generator, the scheme and theory of which were given by N. G. Basov and A. M. Prokhorov¹⁵ even before the publication of Townes’s analogous work in the USA. This generator is a peculiar self-oscillating system with feedback, based on quantum effects, consisting of a molecular beam and a resonator through whose cavity this beam passes.

The frequency of the system generating radio waves, as it turns out, is determined with a very high degree of accuracy by the period of oscillation of self-excited gas molecules. In the several such systems already implemented, the line of the so-called “inversion” spectrum of NH$_3$ molecules*) is used. Thus, we are dealing with a peculiar kind of “clock,” the role of whose “pendulum,” roughly speaking, is performed by the nitrogen atom in the ammonia molecule, interacting with “quanta of radio radiation.”

It has now been shown that by this method one can realize a time “standard” with an absolute stability (reproducibility) of the order of $10^{-9}$.

At FIAN, and subsequently, according to the schemes developed there, at a number of other institutes of the USSR, several such instruments have been built. Until recently, similar equipment existed only in the USA. The possibility thus opened up of realizing atomic clocks with an accuracy of the order of $10^{-9}$ is significant for a variety of applications. Along with the solution of broad problems of a theoretical character (such as, for example, the possibility of verifying certain conclusions of the general theory of relativity), great prospects also arise for applications in the field of technology. Thus, here too we have a vivid example of the interconnection of science and technology discussed above.

The methods of radio spectroscopy equip the research physicist with new powerful means of investigation, having manifold applications in various areas of the science of matter.

By way of illustration one may cite the list of topics represented in FIAN’s works that are carried out using this method: such are molecular spectroscopy (the fine and hyperfine structure of rotational spectra of molecules and, in particular, the spectra of the internal rotation of molecules), magnetic and electric (multipole) moments of atomic nuclei, valence states of activators in phosphors, the study of free radicals, and so on.

In a short time the oscillations laboratory of FIAN substantially altered and reoriented its subject matter in accordance with those shifts and at those rates that are characteristic of the evolution of physics in recent decades.

Still more radical changes of subject matter, as well as of method, are characteristic of the group of nuclear laboratories, as we have already

*) The use of ND$_3$ is also envisaged.

noted above. Here—in the field of elementary-particle problems—we are dealing with the front line of science, which in recent times has shifted in such a way that, as science progressed, it became necessary to deal with new objects of research—with a realm of qualitatively new phenomena.

The development of the group of the Institute’s laboratories engaged in research in the field of the solid state and optics was of a different character. In some cases here too, in recent times, there has been a radical change in the range of problems, caused by the emergence into the foreground of one or another circle of questions that had acquired sharply topical interest. An example of this may be the reorientation of significant efforts of the dielectric-physics group toward the study of semiconductors.

However, the fundamental foundations on which the development of many directions in the indicated field was built had already been laid by discoveries dating from the period preceding the founding of the Institute.

Combinational scattering of light, for example, was discovered (independently of Raman) by L. I. Mandelstam and G. S. Landsberg as early as the end of the 1920s of this century.^16

On the basis of this discovery, the laboratory of FIAN, which for almost 25 years until his death was headed by G. S. Landsberg, carried out enormous work using also the possibilities of infrared spectroscopy. A vast amount of material has now been accumulated from experimental and theoretical research, as a result of which it has become possible to “throw a bridge” linking the sufficiently well-studied picture of the optical spectra of many organic substances with the structure of the complex molecules of these substances. This many-year work, which also has great practical significance, makes it possible to determine the structure of molecules and their characteristic parameters by deciphering spectroscopic data.

The development of the subject matter of the indicated laboratories proceeded mainly in the direction of its deepening and expansion.

At the present time technology sets physics (and, moreover, in its various fields and in various aspects) the task of obtaining new materials with predetermined specific properties, especially valuable for one or another branch of technology.

In some cases it proves possible to approach the solution of such tasks on the basis of theoretical considerations and models. An example may be the outstanding achievement of the laboratory headed by B. M. Vul—the discovery of special properties (dielectric and piezoelectric) of barium lead zirconate titanate and a number of other works that followed this discovery.^17

The luminescence laboratory has created an entire series of new phosphors necessary for solving extremely urgent problems of the latest technology.

Below we give a somewhat more detailed survey of the subject matter of the Institute’s laboratories, omitting what has already been said in the preceding general outline of its work.

Work in the field of theoretical physics. Above, mention has already been made of some of the largest achievements and of the general direction of the work of the theoretical department, headed since its foundation by I. E. Tamm.

In modern elementary-particle physics, in the search for a new theory, it is very important to have new ideas, new attempts at resolving difficulties.

A final judgment about their fruitfulness will be given in the future. One such attempt—the idea of nonlocal interactions, which later became popular and was developed in many countries—was put forward and developed by M. A. Markov1; another—the theory of particles with variable spin—was developed in the works of V. L. Ginzburg and I. E. Tamm and their collaborators. At the new stage of the theory, a major role was played by studies on the problems of so-called renormalizability and dispersion relations (E. S. Fradkin and V. Ya. Fainberg). Works on quasi-poles, on the theory of damping, and on variational methods of investigation belong to the same circle.

Among the works of recent years, carried out in contact with other laboratories, one may note: the development of the theory of multiple generation of particles and, in general, of the theory of processes at ultrahigh energies (S. Z. Belenkii and D. S. Chernavskii); the proposal of new ideas and the development of a theory of the origin of cosmic rays, which made it possible to establish a connection between these ideas and radio-astronomical data (V. L. Ginzburg)2.

Mention should also be made of work on the theory of variations of cosmic rays, on neutron physics, and on processes at high energies (E. L. Feinberg).

It is difficult to enumerate everything done by the theoretical department in close connection with the work of the various laboratories of the Institute.

We can only note very briefly that, in this same theoretical department, work has been carried out on the physics of the solid state and of low temperatures (the phenomenological theory of superconductivity, the thermodynamic theory of ferroelectrics, work on the electrical conductivity of metals, etc.—V. L. Ginzburg3), on the theory of interaction in a system of many particles and on the application of this theory to metals and plasma (V. P. Silin), on the statistical theory of many particles, on hydrodynamics (including the theory of the condensation shock—S. Z. Belenkii), and on magnetohydrodynamics.

All this shows that the work of the theoretical department, over the more than twenty years of its existence, was built on the principle of combining “abstract” questions of theory (mainly the theory of elementary particles) with broadly conceived investigations into the most diverse problems of physics, arising from friendly contact with the experimental laboratories of the Institute.

Work in the field of nuclear physics. As already mentioned above, the development of work on nuclear physics and cosmic rays began as early as 1933. Soon the direction of these investigations was headed by D. V. Skobeltsyn.

1. We have already spoken of the development of the work of FIAN on the study of cosmic rays and of its principal results. It was begun as early as 1934. At the same time, expeditionary work also unfolded (participation in the Elbrus expeditions).

During the war, the study of cosmic rays was suspended until 1944. In 1944 the first expedition to the Pamirs was carried out (3860 m above sea level), and in 1947 a permanent high-mountain scientific station was founded there. The principal leading core of the cosmic-ray laboratory is the group consisting of N. A. Dobrotin (head of the laboratory), N. G. Birger, S. N. Vernov, G. B. Zhdanov, G. T. Zatsepin, S. I. Nikolsky, I. L. Rozental, A. N. Charakhchyan, A. E. Chudakov, and others.

In 1945, work was begun—and until recently has been successfully developing—on the study of “wide” atmospheric showers over the entire energy range of the primary particles that produce them \((10^{13}—10^{17}\ \mathrm{eV})\)4.

At first these investigations were directed toward detecting extremely large showers (consisting of tens or on the order of a hundred million particles) and studying their peripheral structure. They led (by the beginning of the 1950s) to the establishment of a certain “record” in the observation of showers of extremely high energy. Only recently (in England and the USA) has it become possible to observe still more powerful showers; moreover, work oriented in this direction is now acquiring particular relevance from the standpoint of the cosmo-physical aspect of the problem.

The investigations of the Pamir station and at sea level in recent years have been devoted mainly to the study of the central regions—the trunks of the shower, where particles of especially high energy are concentrated. On a broad front, using for observations in the stratosphere the method of “teleobservation” with the transmission of signals by radio, as well as flights of an airplane with a Wilson chamber installed in it, and, in recent times, photographic emulsions as well, other investigations of electron-nuclear showers and the phenomena connected with them are being carried out at different altitudes.

Mention should be made of methodological developments that made it possible to develop many of the investigations mentioned above. This concerns the use in various physical instruments of gas-discharge lamps with a cold cathode (L. N. Korabelev). Initially these lamps were used to create compact and economical hodoscopes. But subsequently it proved possible to use them also for constructing various instruments serving to measure the intensity of radioactive radiations, counting circuits, amplitude analyzers, millisecond timers, various counting devices, etc. Many of these instruments have already been adopted by industry. In essence, L. N. Korabelev succeeded in creating a new direction in the use of “cold thyratrons.”

Another direction in the study of cosmic rays is being developed in the laboratory of A. I. Alikhanian (M. I. Daion, V. G. Kirillov-Ugryumov, and others), which joined the Institute in 1951. Here the mass spectrum of cosmic-ray particles is studied. A. I. Alikhanian’s laboratory conducts this work with the aid of the so-called magnetic mass spectrometer developed by him, relying mainly on the high-mountain station on Mount Aragats (Armenia).

In recent years the laboratory has devoted considerable effort to the development of a new method of investigation, in which the magnetic mass spectrometer is combined with a Wilson chamber containing absorber plates.

Having carried out a great deal of work to improve the apparatus, the laboratory began to obtain data on mesons with masses of about 950 and 550 electron masses. Of particular interest are indications of the existence of a particle with mass \(550 m_e\), not yet observed in experiments of other laboratories.

With the aid of the magnetic mass spectrometer, A. I. Alikhanian’s laboratory studied the momentum spectra of \(\mu\)- and \(\pi\)-mesons, protons, and electrons of cosmic rays.

1. The development of nuclear physics insistently required finding ways of artificially accelerating particles to relativistic energies.

We have already spoken^22 about the work of V. I. Veksler, who discovered the so-called principle of autophasing, which led to decisive success in this direction.

Veksler proposed several types of accelerators based on the use of this principle, which subsequently received the names: synchrotron, phasotron (synchrocyclotron), and microtron.

The first years of activity of the laboratory of accelerators and photonuclear reactions, headed by V. I. Veksler, were devoted entirely to the task—

...the practical realization of synchrotron-type accelerators. As early as 1947, a 30-million-electron-volt synchrotron and a betatron of 3 MeV were put into operation in the laboratory (the first in the USSR). The design of a second, more powerful, 250 MeV synchrotron also belongs to this same period of time*). This synchrotron was commissioned in 1949.

The development of the theory and of the problems of designing new accelerators proceeded successfully. In a comparatively short time various versions of cyclic accelerators were proposed and theoretically considered. At present the possibility of using a new, so-called coherent method of acceleration is being investigated ^23.

Since 1953 the laboratory has been carrying out theoretical and, more recently, experimental research on the realization of a new accelerator with a constant magnetic field—the so-called ring phasotron ^24. In all this extensive work the participants have included, and continue to include, besides V. I. Veksler, A. A. Kolomensky, V. A. Petukhov, V. E. Pisarev, M. S. Rabinovich, and P. A. Cherenkov.

The construction in the laboratory of electron accelerators of 30 MeV and 250 MeV laid the foundation for the broad development of investigations into the nuclear interaction of high-energy photons. The study of this type of interaction is one of the most important problems of modern physics, since experiments with high-energy photons have the advantage that the properties of the electromagnetic field are well known, and therefore the theoretical interpretation of the results of these experiments is in many cases simpler and more definite than in the case of purely nuclear interactions.

In addition to experimental investigations, theoretical work is also being carried out on a very broad scale, under the direction of M. A. Markov.

The laboratory has conducted investigations along two main lines:

a) the study, by the method of photonuclear reactions, of phenomena of interest in connection with the problem of the structure of atomic nuclei, and

b) the study of the properties of the meson field and of nucleons by investigating the photoproduction of mesons and the processes of meson formation in photonuclear interactions.

In the first of the two main directions indicated, one may note the work on the photodisintegration of the light nuclei of deuterium and helium (by the Wilson-chamber method—A. N. Gorbunov). In the latter case, data were obtained on the role of the mechanism of the two-nucleon “quasideuteron” model, on the role of exchange forces, etc.

A large cycle of work ^25, carried out by the section headed by L. E. Lazareva, using the 30 MeV synchrotron, was devoted to the study of the complex of phenomena in the region of the so-called “giant resonance.” Substantial results were obtained, in particular, on revealing the role of the mechanism of the “direct” photoeffect, on the influence of the shell structure of nuclei, etc. The mechanism of photofission of uranium and thorium nuclei was investigated.

In the second of the above-mentioned directions, of particular interest are the studies of meson formation near the threshold of this process, carried out on the initiative of M. A. Markov and A. M. Baldin; the work on studying the spin-isotopic symmetry of the meson field and determining the sign of the meson charge of the neutron ^26 (photoproduction of \(\pi_0\)-mesons on deuterium nuclei) ^27; studies of the photoproduction of \(\pi\)-mesons; observations of the Compton effect on protons (V. I. Goldansky), and many other works.

*) A. P. Komar, P. A. Cherenkov, and M. S. Rabinovich took part in directing the work on the construction of this synchrotron.

3. Studies of nuclear reactions at low and intermediate energies up to 1945 were carried out at FIAN on a small scale.

Among the extensive investigations of the prewar period one should mention a cycle of works using the Wilson chamber method on the study of pair formation under the action of RaC $\gamma$-rays (L. V. Groshev and I. M. Frank).

The problem of atomic energy posed many new problems of considerable complexity for neutron physics. In connection with this, in the postwar years the atomic-nucleus laboratory headed by I. M. Frank carried out a number of theoretical and experimental works on questions of diffusion and absorption of neutrons, as well as their multiplication in fissile substances. Entirely different requirements had to be imposed on the accuracy of neutron measurements, which forced a substantial improvement of their methodology. To study questions necessary for understanding the physics of neutron processes in reactors and for measuring the parameters characterizing them, special subcritical models of uranium-graphite reactors were constructed. On these models, using the so-called prism method, an extensive series of works was carried out, which in many respects clarified the mechanism of neutron processes occurring in reactors, and the values of a number of essential parameters were obtained[^28].

Subsequently, special attention was paid to the study of the simplest nuclear reactions.

A new method was proposed[^29] and developed for neutron spectroscopy by slowing-down time in lead.

In contrast to the generally accepted method of neutron spectrometry by time of flight, the new method has a “luminosity” greater by 2–3 orders of magnitude and is convenient for measuring partial cross sections of reactions caused by neutrons[^30]. Although the resolving power of the spectrometer is not high, it depends only weakly on neutron energy. All this made it possible successfully to apply this method to the study of neutron reactions in the region of neutron energies, difficult to access for study, in the tens of kiloelectronvolts (F. L. Shapiro). With the aid of a pulsed neutron source, investigations of questions of neutron diffusion were also carried out by the so-called method of nonstationary diffusion[^31].

Another line of work was the study of nuclear reactions on light nuclei. In particular, the nuclear reaction of the deuteron with tritium was subjected to a very detailed investigation (E. M. Balabanov, I. Ya. Barit, L. N. Katsaurov, I. M. Frank, I. V. Shtranikh).

Considerable work was carried out in nuclear electronics and, in particular, on the creation of multichannel amplitude and time analyzers (I. V. Shtranikh).

Beginning in 1946, a cycle of works was carried out by the photoemulsion technique. The nuclear laboratory took an active part in the initial stage of work on organizing the production of domestic thick-layer plates.

Irradiation of photoemulsions at the phasotron of the Joint Institute for Nuclear Research (JINR) made it possible for the laboratory to study the fission of uranium nuclei at high excitation energies (fission by fast neutrons and by absorption of slow $\pi$-mesons)[^32]. Work is also being conducted at the JINR phasotron on the study of $\pi$-meson scattering.

An independent line of work consisted of investigations in the field of nuclear paramagnetism (K. V. Vladimirsky). The development of these works made it possible, for example, to create a very sensitive method for analyzing the composition of heavy water[^33].

In 1950 a laboratory of isotopes and radiations was organized, now headed by V. A. Korotkova. The laboratory was faced with ...

the task was set of introducing the methods of nuclear physics into technology and into various fields of scientific research.

Work on defectoscopy using radioactive radiations, the foundations of which had been laid during the war years, acquired in this laboratory an entirely different scope. Its practical significance was determined by the possibility of wide application of artificial radioactive substances as sources of radiation.

The absorption of $\beta$- and $\gamma$-rays and the reflection of $\beta$-rays were used in developing methods for the precise measurement of thicknesses, necessary for solving many technical problems (the thickness of cold and hot rolled products, the thickness of coatings, etc.). A number of instruments developed jointly with the Central Laboratory of Automation are being successfully used in industry.

At present the measurement of wear of machines by the method of labelled atoms is widely employed. The laboratory took an active part in the development of this method.

The laboratory is also engaged in improving methods for observing the absorption and scattering of beta and gamma radiation and methods for measuring small currents, necessary for solving practical problems.

A practicum on the physical foundations of the method of radioactive indicators has been organized at the laboratory; it trains scientific and engineering-technical workers of branch institutes and factories who are not specialists in nuclear physics. In the seven years of the laboratory’s existence, 500 people have been trained in the practicum. The number of consultations given by the laboratory staff is very large.

There is no doubt that, as a result of its work, the laboratory has contributed substantially to the introduction of the methods of nuclear physics into technology.

Work in the field of radiophysics. In the prewar period the study of the propagation of radio waves over the earth’s surface occupied the principal place in the work of the Physical Institute of the Academy of Sciences in this field*.5

At that time many of the basic features of the process of radio-wave propagation remained unclear, and there were disputes concerning the most fundamental characteristics—for example, the question of how the propagation velocity depends on the electrical properties of the Earth’s surface. It is easy to imagine how important all this was, if only for the problems of radio navigation. Proceeding from optical methods, L. I. Mandelstam and N. D. Papaleksi created a remarkable method for radio-interferometric measurement of distances, which, on the one hand, made it possible to investigate even very fine features of the phenomenon and, on the other, in the form of the radiodalnomer and other instruments, was widely introduced into practice and served as the beginning of a new field of radiophysics—radiogeodesy. On the basis of the theoretical, experimental, and design work carried out within the laboratory by Ya. L. Alpert, V. V. Migulin, P. A. Ryazin, E. Ya. Shchegolev, and others,[^35] and later by A. B. Melikyan, and also thanks to the study of the propagation of radio waves in various regions of our country, a number of important results were obtained, of great fundamental theoretical and practical significance.

Supplemented by the theoretical investigations of L. I. Mandelstam, M. A. Leontovich, V. A. Fock, E. L. Feinberg (FIAN), and G. A. Grinberg (LFTI), these works made it possible to create a clear picture of the entire process of radio-wave propagation.

Another direction of the laboratory’s work was research in the field of the theory of oscillations. Among these it is necessary to note the development of the theory

frequency stabilization of vacuum-tube oscillators and the theory of self-oscillations in nonlinear distributed systems (S. M. Rytov, A. M. Prokhorov).

The study of the properties of substances at ultrahigh frequencies by means of an original, so-called thermometric method of measuring losses was successfully pursued, even in the prewar period, by talented young staff members of the Institute, M. A. Divilskii and M. I. Filippov. Along with a number of methodological results, they obtained interesting data on the electrical and magnetic parameters of a number of substances. Work in this direction (studies of the properties of ferrites, etc.) continues even now (D. I. Mash).

From 1945 on, a group was formed in the laboratory for the study of the structure of the ionosphere and the propagation of radio waves in it (headed by Ya. L. Alpert). At present this work has been transferred to the Institute of Terrestrial Magnetism, the Ionosphere, and Radio-Wave Propagation of the Ministry of Communications.

In recent years a number of new directions have arisen. Work in theoretical radiophysics is concentrated chiefly on problems of statistical radiophysics. A general theory of electrical fluctuations was developed,^[36] encompassing, as limiting cases, the theory of thermal radiation and the theory of noise in electrical circuits. Recently a theory of thermal fluctuations in a dispersive medium was constructed, and on this basis a theory of Rayleigh scattering of light in such a medium was given. Work in this field is being carried out by the theoretical sector of the oscillations laboratory (S. M. Rytov).

From 1952 on, work in radiospectroscopy, of which we have already spoken, began to develop. In addition to what has already been said above, mention should be made of work on electron paramagnetic resonance.

In connection with the development of the “molecular generator,” methods were proposed for obtaining active molecules that initiate the oscillations of the generator. One of the proposed methods is currently being used to create low-noise amplifiers employing the phenomenon of paramagnetic resonance. A theory of the molecular amplifier was also developed. At present work is being completed on the creation of a model of an “atomic clock” (N. G. Basov, I. V. Shtranik).

In the postwar period, a new branch of astrophysics—radio astronomy, concerned with the radio emission of cosmic objects—began to develop rapidly in various countries. It turned out that radio astronomy opens up entirely new possibilities for studying processes on the Sun, the characteristics of individual cosmic bodies, nebulae, the Galaxy, and the Universe as a whole.

On the initiative of N. D. Papaleksi, the oscillations laboratory took part in an expedition to Brazil (1947) to observe the radio emission of the Sun during an eclipse.

Subsequently, radio telescopes for various wavelengths were built, and important studies were carried out on the propagation of radio waves in the atmosphere using extraterrestrial sources. In the radio-astronomy group of the Institute, headed by V. V. Vitkevich, A. E. Salomonovich, B. M. Chikachev, and others are working. The study of extraterrestrial emitters led to a number of interesting conclusions about the radio emission of the Moon (both at centimeter and millimeter wavelengths) and about the radio emission of the Sun. The study of the solar corona by the passage through it of the radio emission of the Crab Nebula showed that the Sun has a “supercorona” extending to a distance of many solar radii.^[37]

In the laboratory’s work on radio astronomy, considerable attention had to be devoted to designing various apparatus for different wavelengths.

waves. At present the construction of a unique radio telescope is being completed, and work is also under way on the construction of a large radio telescope in the form of a “cross” for the study of metagalaxy.

The Physics Institute was the first scientific institution in the Soviet Union to successfully develop radio-astronomical research, both experimental and theoretical (V. L. Ginzburg), and thereby substantially promoted the initiation of this work not only at the Pulkovo Observatory, where this work is being carried out under the direction of S. E. Khaikin, who moved there in 1953 from FIAN, but also in other institutes of the country.

Work in the field of luminescence and optics. As is known, the investigations of S. I. Vavilov and his school made a major contribution to the theory of luminescence and exerted a strong influence on the development of this field of physics.

The subject matter of the laboratory created by S. I. Vavilov and now bearing his name encompasses a wide range of questions connected with the luminescence of liquid and solid substances.

The leading scientific staff of the laboratory includes V. L. Levshin (head of the laboratory), M. N. Alentsev, V. V. Antonov-Romanovskii, M. D. Galanin, N. D. Zhevandrov, M. A. Konstantinova, Z. L. Morgenshtern, Z. A. Trapeznikova, L. A. Tumerman, S. A. Fridman, and A. A. Cherenev. At a certain stage E. I. Adirovich and D. I. Blokhintsev took part in the theoretical work.

The laboratory conducts research in almost all the principal areas of luminescence. At present, however, the greatest attention is devoted to the study of electroluminescence, scintillation emission, and cathodoluminescence, which have recently acquired especially important scientific and technical significance.

In the laboratory, various types of interactions of luminescing molecules with one another or with molecules of the medium in which they are located have been studied. A theory has been created for the resonant transfer of excitation energy in luminescing media and of the processes of migration quenching and depolarization at high concentrations of the luminescent substance ^38, ^39. At the same time, physicochemical interactions were also studied, leading to concentration quenching and to changes in the spectra of luminescent substances.

The conditions for the occurrence of mirror symmetry of absorption and emission spectra were clarified. By means of studies of polarization phenomena, the motions of molecular oscillators and their arrangement in crystals and molecules were investigated. Substantial data were obtained on the long-lasting emission of molecules in a biradical state ^40.

One of the most important characteristics of luminescence processes is the lifetime of the excited state. In this connection, the laboratory devoted much attention to the study of the lifetimes of excited states of molecules and the influence of various factors upon them. New methods were developed for investigating very short-lived emission processes of approximately \(10^{-9}\) sec ^41.

Another important section of the laboratory’s work was the study of the kinetics and energetics of the emission of crystal phosphors.

The recombination character of the emission was firmly established; the levels of localization of electrons and holes, the illuminating action of infrared rays and of the exciting light itself, and nonlinear excitation effects were studied; a number of data were obtained on the luminescence centers of phosphors.

The totality of these works made a major contribution to the development of the theory of the luminescence of crystal phosphors40, 41.

In a number of works the absolute luminescence yield in various crystals—scintillators—was determined, the process of energy transfer from the host substance to the luminescence center was studied, and ideas were obtained concerning the development of individual scintillations39.

The laboratory’s work is closely connected with industry. In 1937–1941, under the direction of S. I. Vavilov, the first luminescent light sources were developed and transferred to industry; they played a very large role in preparing the way for the ever-expanding production of luminescent lamps, which yield an enormous economic effect. The laboratory was the first to develop methods of quantitative luminescent analysis42.

Much attention was devoted to the development and study of phosphors that give a brief flash under the influence of an external action. These works also had not only theoretical but also applied significance. Recently the laboratory has developed a new type of phosphor of continuous action with artificial radioisotopes, several times superior in brightness and service life to the luminous compositions used earlier. The laboratory has also created a number of other luminophores important for various branches of technology and the national economy40, 41.

In the development of work on physical optics at the Institute, a major role belonged to L. I. Mandelstam, M. A. Leontovich, and G. S. Landsberg—the permanent head of the optical laboratory from the time of its formation in 1934.

Under G. S. Landsberg’s direction a large group of his students grew up. Many of them are at present leading members of the optical laboratory (P. A. Bazhulin, V. I. Malyshev, G. P. Mogulevich, M. M. Sushchinskii, I. L. Fabelinskii).

Investigations on the combination scattering of light became the basis for work on molecular spectroscopy and the study of the structure of molecules by optical methods (as we have already said).

In connection with this, it is necessary to note the following directions of work:

1. The development, in collaboration with the Institute of Organic Chemistry, of methods for the molecular analysis of petroleum and gasolines, which found broad practical application.

2. Investigations of intermolecular interactions and, first of all, of the hydrogen bond43. Work on the theory of characteristic spectra. At the same time, the large body of factual material on combination-scattering spectra obtained in the laboratory made it possible to broaden the concept of characteristicity and to identify characteristic structural elements of molecules, using for this purpose the whole set of parameters of the lines of combination scattering44.

Work on molecular optics was represented chiefly by studies of the molecular scattering of light in the condensed phase. The scattering of light, as was shown by L. I. Mandelstam (1918–1926), is directly connected with the propagation of ultrasonic waves in a substance45. Therefore, alongside the study of the spectral composition of scattered light (I. L. Fabelinskii46), the range of interests of the Optical Laboratory also included investigations of hypersonic and ultrasonic waves (P. A. Bazhulin)47, 48. Naturally, this range of questions required the study of the scattering of light both in solids and in liquids of various viscosity. A [[unclear: sentence continues on next page]]

the theory of light scattering in crystals, which proved to be in good agreement with experiment[^49]. From the fundamental point of view, studies of light scattering by nonuniformly heated media were of great significance. Taken together, these works led to a new understanding of the phenomenon of the scattering of high-frequency waves in matter.

In recent years, research in molecular optics has been extended to the phenomena of the optics of metals. Measurements of optical constants made it possible to determine the concentration of conduction electrons in silver and the upper limit for this quantity in tin and lead.

Studies in atomic spectroscopy were begun at the Institute in 1935. At first the direction of these works was questions of spectral analysis. These studies acquired especially important practical significance during the Great Patriotic War and in the years that followed. They were broadly developed in the laboratory of spectral analysis organized in 1944 (headed by S. L. Mandelstam). A number of practical methods and new instruments for spectral analysis were developed; among them one should mention the creation of new styloscopes, which played an important role in the work of defense plants (S. L. Mandelstam, L. M. Ivantsov, S. M. Raiskii), the development of an “evaporation method”[^50], which ensured a previously unattainable sensitivity of analyses and was applied to the analysis of uranium for purity and to other tasks, and the development of new, rapid and accurate, automated photoelectric installations.

A very extensive place in the work of the laboratory was occupied by the development of the physical foundations and theory of spectral analysis. These works made a serious contribution to the transformation of spectral analysis from an empirical method into an independent scientific discipline resting on a serious theoretical foundation and possessing a highly developed experimental technique[^51].

Another direction of the laboratory’s work is research in the spectroscopy of the gas discharge. In an extensive cycle of theoretical and experimental works, a new hydrodynamic theory of the spark discharge and original research methods were developed, which made it possible to obtain important information on the processes of excitation, ionization, and radiation of gases in the state of a high-temperature plasma[^52].

At present the principal direction of the work of the spectral-analysis laboratory has become research in atomic spectroscopy. Here one may note the development of approximate methods for calculating, with the aid of electronic computing machines, the wave functions of atoms, theoretical and experimental studies of the processes of collisions of atoms with slow electrons, questions of broadening of spectral lines, etc.[^53], which have already yielded a number of interesting results.

Extensive studies were carried out at the Institute in the spectroscopy of flames. Under the direction of N. N. Sobolev (flame-optics sector), optical methods were developed for measuring the temperature of heated gases and flames as applied to specific practically important objects[^54]. A systematic pyrometric study was made of a number of technical flames, including the plume of a liquid-propellant rocket engine. Simultaneously with the development of flame pyrometry, the shape and widths of spectral lines in flames and arcs were investigated[^55],[^56].

At present, in the flame-optics sector, studies are being conducted of physical processes in gas behind a shock wave and in arcs burning in noble gases.

D. V. SKOBELTSYN AND I. M. FRANK

Works in the field of semiconductors and dielectrics. During the initial period (beginning in 1933), the principal workers of the dielectrics laboratory were B. M. Vul, I. M. Goldman, and G. M. Kovalenko. Later, G. I. Skanavi, S. V. Bogdanov, and others also took part in the work of this laboratory.

In its first years the dielectrics laboratory carried out investigations of the electrical strength of gases at various pressures.

Alongside electrical phenomena in gases, solid dielectrics were also studied.

Investigations of solid, chiefly ceramic, dielectrics were undertaken during the years of the Patriotic War with the aim of developing ceramic capacitors. They culminated in the discovery, in 1944, of ferroelectric phenomena in barium titanate. These works were published in 1945–1957. Immediately thereafter the laboratory carried out a whole series of experimental studies in which the basic properties of barium titanate as a new ferroelectric were revealed and studied.

At the present time it has acquired major practical significance, and the laboratory, together with branch research institutes and industry, has carried out an enormous amount of work that made it possible to bring this discovery into practice.

The thermodynamic theory of ferroelectric phenomena in barium titanate was developed by V. L. Ginzburg^58. The laboratory’s work on titanates gave rise to the development of numerous investigations in this direction both in the USSR and abroad.

The works carried out in recent years under the direction of G. I. Skanavi* are aimed at studying the phenomena occurring in solid crystalline and amorphous dielectrics under the action of an electric field. In this work, research proceeded in the direction of investigating the physics of dielectric polarization, in particular the relaxation polarization of solid dielectrics^59,60, and also of studying electronic processes in crystalline dielectrics in strong fields, which ultimately lead to a breakdown of electrical strength.

Work on the study of electrets led to the discovery of a new class of electrets made of inorganic polycrystalline dielectrics, which possess very great stability and a large charge^61.

The investigation of relaxation polarization in solid dielectrics led to the discovery of a new class of solid dielectrics—strontium-bismuth titanates with very high dielectric permittivity (1000 and higher), not possessing ferroelectric properties. The work was based on the idea that the combination of an internal field favorable to polarization, created in the perovskite structure, with the relaxation polarizability of weakly bound ions leads to very high dielectric permittivity without ferroelectric properties^62. The new dielectrics have already found application in the manufacture of special capacitors.

With the aid of a specially developed refined technique, a number of regularities have been obtained that are of interest for the physics of electrical breakdown and electrical conductivity of crystals^63.

Recently, the laboratory has begun investigating the influence of various kinds of irradiation on the structure and properties of a dielectric.

Since 1950, investigations on dielectrics have also been extended to semiconductors, which, as is known, are dielectrics

* The group under his direction was separated into an independent laboratory in 1954.

with a small forbidden-band width. These works, under the direction of B. M. Vul, are now being carried out (in the Semiconductor Laboratory) by a group that includes E. I. Adirovich, A. V. Rzhanov, V. S. Vavilov, V. A. Chuenkov, and others.

After the successful completion of the methodological stage of the work in the laboratory, the first samples of point-contact (1950–1951) and then, in 1953, planar germanium diodes and triodes were created, and a comprehensive investigation of them was carried out. A theory of pulse propagation in semiconductor devices was developed, which is of considerable interest for the use of these devices in computing-and-solving devices[^64].

At present the laboratory is carrying out work on the study of the action of neutrons and fast electrons on germanium. In this field a number of interesting regularities have been established. They have made it possible to study the influence of various factors on the conversion of the energy of β-radiation into electrical energy, effected with the use of semiconductors[^65].

Similar investigations have also been carried out on irradiation with fast neutrons. Finally, in the field of photoelectric phenomena, the conversion of light energy into electrical energy by means of silicon photoelements is being studied.

Much attention is also being devoted to the study of recombination processes in the volume of a crystal and on its surface, which play an essential role in all electronic processes in semiconductors. The effective recombination cross sections for individual impurities and the influence of various factors on the rate of surface recombination are being studied[^66].

Among works of fundamental importance one should note the theory of electrical breakdown in semiconductors. Using the laboratory’s experimental investigations of ionization processes in semiconductors placed in strong electric fields, B. M. Vul showed that, in breakdown here, a process takes place completely analogous to that described by the theory of breakdown in gases[^67].

In the numerous staff of the P. N. Lebedev Physical Institute of the Academy of Sciences of the USSR there work scientists conducting research in the most diverse areas of physical science. The subject matter of the work covers the entire range from purely theoretical problems, developing the foundations of natural science, to problems of immediate applied significance. The survey given in the article, not claiming completeness, is inevitably more a list than an exposition of the essence of the numerous results obtained. In the list of references, too, it has been necessary to confine oneself to indicating only a comparatively small number of principal works. The number of works published annually by the Institute in recent years has reached several hundred, and it is impossible to give their complete list here.

The many-sidedness of the Institute’s subject matter is, evidently, a great strength. To some extent, the solution of any serious problem requires an integrated approach. At the same time, with the contemporary development of science, each individual worker can be useful only in solving a comparatively narrow range of problems. Therefore the joint work of specialists of different profiles opens up great possibilities for the Institute.

Together with the entire country, the P. N. Lebedev Physical Institute of the Academy of Sciences of the USSR has, over the past years, traversed a tremendous path of development. Исклю-

...the considerable opportunities for scientific work which the Institute now possesses impose great obligations. The staff of the Physics Institute understands its responsibility to the Socialist Motherland.

CITED LITERATURE

1. S. I. Vavilov, The Physics Cabinet—the Physics Laboratory—the Physics Institute of the Academy of Sciences of the USSR over 220 Years, Publishing House of the Academy of Sciences of the USSR, Moscow–Leningrad, 1945.

2. B. M. Vul and I. M. Tamm, JETP 4, 1613 (1934).

3. V. I. Veksler, A. A. Kolomenskii, V. A. Petukhov, and M. S. Rabinovich, Atomic Energy, Suppl. to No. 5, 1957.

4. V. A. Petukhov, M. S. Rabinovich, L. P. Zinov’ev, and I. S. Danilkin, Proc. CERN, No. 1, 513 (1956).

5. S. N. Vernov, N. L. Grigorov, N. A. Dobrotin, S. P. Sokolov, F. D. Savin, and A. I. Kurakin, DAN SSSR 68, 253 (1949).

6. G. T. Zatsepin, V. I. Veksler, N. A. Dobrotin, G. T. Zatsepin, L. V. Kurnosova, L. A. Lyubimov, I. L. Rozental’, L. Kh. Eidus, JETP 19, 826 (1949).

7. G. T. Zatsepin, DAN SSSR 67, 993 (1949).

8. D. V. Skobel’tsyn, UFN 41, 331 (1950).

9. Materials of the III All-Union Conference on the Physics of Cosmic Rays, Izvestiya AN SSSR, XIX, Nos. 5–6, 1955; XX, No. 1, 1956.

10. I. E. Tamm, Journal of Physics 9, 445 (1945); UFN 56, 569 (1955).

11. S. Z. Belen’kii, a) Avalanche Processes in Cosmic Rays, Gostekhizdat, 1948; b) Izvestiya AN SSSR (phys. ser.) 19, 611 (1955).

12. P. A. Cherenkov, DAN 2, 451 (1934); S. I. Vavilov, DAN 2, 457 (1934); P. A. Cherenkov, Trudy FIAN 2, No. 4 (1944).

13. I. E. Tamm and I. M. Frank, DAN 14, 107 (1937); see also the review—B. M. Bolotovskii, UFN 62, 201 (1957).

14. S. E. Khaikin and B. M. Chikhachev, DAN 58, 1923 (1947).

15. N. G. Basov and A. M. Prokhorov, JETP 27, 431 (1954).

16. G. S. Landsberg and L. I. Mandel’shtam, Naturwissenschaften 16, issue 27, 557–558 (1928).

17. B. M. Vul, “Elektrichestvo,” No. 3, 12 (1946).

18. M. A. Markov, UFN 51, 317 (1953).

19. V. L. Ginzburg, UFN 62, 37 (1957).

20. V. L. Ginzburg, UFN 42, 169 (1950); 48, 25 (1952); JETP 31, 202, 541 (1956).

21. N. A. Dobrotin, Cosmic Rays, Gostekhizdat, 1954.

22. V. I. Veksler, DAN 43, 346 (1944); DAN 44, 393 (1944); Journal of Physics 9, 153 (1945).

23. V. I. Veksler, Atomic Energy, No. 5, 427 (1957).

24. A. A. Kolomenskii, V. A. Petukhov, M. S. Rabinovich, PTE, No. 2, 26 (1956).

25. L. E. Lazareva, B. S. Ratner, et al., Proceedings of the Session of the Academy of Sciences of the USSR on the Peaceful Uses of Atomic Energy in 1955, p. 306; JETP 33, 53 (1957); DAN 102, No. 2 (1955); 32, 27 (1957).

26. A. M. Baldin and V. V. Mikhailov, DAN 91, 479 (1953); Nuovo Chim. 3, No. IX, p. 4 (1955).

27. A. S. Belousov, A. V. Kurenko, E. I. Tamm, DAN 102, 921 (1955); M. I. Adamovich, V. I. Veksler, et al., Proc. CERN 2, p. 265 (1956); DAN 102, 715 (1955).

28. L. V. Groshev, O. I. Kozinets, L. E. Lazareva, K. D. Tolstov, E. L. Feinberg, I. M. Frank, F. L. Shapiro, and I. V. Shtranikh, Proceedings of the Session of the Academy of Sciences of the USSR on the Peaceful Uses of Atomic Energy, July 1–5, 1955, Reports at the Meetings of the Department of Physical and Mathematical Sciences.

29. L. E. Lazareva, E. L. Feinberg, and F. L. Shapiro, JETP 24, 381 (1955).

30. A. A. Berman, M. A. Isakov, I. D. Murin, F. L. Shapiro, I. V. Shtranikh, and M. V. Kazarnovskii, Report P-642 at the International Geneva Conference, 1955.

31. A. V. Antonov, A. I. Isakov, I. D. Murin, V. A. Neunokoev, I. M. Frank, F. L. Shapiro, I. V. Shtranikh, Report P-661 at the International Geneva Conference, 1955.

32. G. E. Belovitskii, T. A. Romanova, L. V. Sukhov, and I. M. Frank, JETP 29, 537, 1955.

33. K. V. Vladimirskii, M. I. Kats, and B. M. Stasovich, Report P-631 at the International Geneva Conference, 1955.

1. Mandelstam L. I. and Papaleksi N. D., Recent studies of the propagation of radio waves along the earth’s surface, OGIZ, 1945.
2. Al’pert Ya. L., Ginzburg V. L. and Feinberg E. L., Propagation of radio waves, Gostekhizdat, 1953.
3. Rytov S. M., Theory of electrical fluctuations, Publishing House of the Academy of Sciences of the USSR, 1955.
4. Vitkevich V. V., DAN 101, 429 (1955).
5. Vavilov S. I., The microstructure of light, Publishing House of the Academy of Sciences of the USSR, 1950, p. 43.
6. Galanin M. D., Resonance transfer of excitation energy in luminescing solutions, Doctoral dissertation, 1955.
7. Levshin V. L., Photoluminescence of liquid and solid substances, Gostekhizdat, 1951.
8. Antonov-Romanovskii V. V., Mechanism of luminescence of alkali-halide phosphors, Doctoral dissertation, Proceedings of FIAN, vol. 2, no. 2/3, 157 (1942).
9. Konstantinova M. A., Chemical fluorescent analysis, Doctoral dissertation, Proceedings of FIAN, vol. 2, no. 2/3, 1942.
10. Landsberg G. S., Izvestiya AN SSSR, ser. phys., no. 3, 373 (1938); no. 1, 5, 13 (1941).
11. Landsberg G. S., Bazhulina P. A. and Sushchinskii M. M., Basic parameters of the spectra of combination scattering of hydrocarbons, Publishing House of the Academy of Sciences of the USSR, 1956.
12. Mandelstam L. I., ZhRFKhO 58, 381 (1926).
13. Fabelinskii I. L., UFN 63, issue 2 (1957).
14. Bazhulina P. A., Absorption of ultrasonic waves in liquids, Doctoral dissertation, Proceedings of FIAN 5, 261 (1950).
15. Mandelstam L. I. and Leontovich M. A., ZhETF 7, 438 (1938).
16. Motulevich G. P., Izvestiya AN SSSR, ser. phys. 11, 390 (1947).
17. Mandelstam S. L., Semenov N. N. and Turovtseva Z. M., Journal of Analytical Chemistry XI, 9 (1956).
18. Mandelstam S. L., Introduction to spectral analysis, Gostekhizdat, 1946.
19. Drabkina S. O., ZhETF 21, 473 (1951); Gegechkori N. M., ZhETF 21, 493 (1951); Dolgov I. G. and Mandelstam S. L., ZhETF 24, 691 (1953); Mandelstam S. L. and Sukhodrev N. K., ZhETF 24, 701 (1953).
20. Mandelstam S. L. and Mazin M. A., Optics and Spectroscopy II, 276 (1957).
21. Sobolev N. N., Optical methods of measuring flame temperatures, Doctoral dissertation, Proceedings of FIAN VII, 161 (1956).
22. Sobolev N. N., Mezhericher E. M. and Rodin G. M., ZhETF 21, 350 (1956).
23. Kitaeva L. F. and Sobolev N. N., Optics and Spectroscopy 1, 302 (1951).
24. Vul B. M. and Goldman I. M., DAN 46, 154 (1954).
25. Ginzburg V. L., ZhETF 15, 739 (1945); 19, 36 (1949); UFN 38, 490 (1949).
26. Skanavi G. I., ZhETF, no. 5 (1947).
27. Skanavi G. I., Electricity, no. 8 (1947).
28. Gubin A. N. and Skanavi G. I., ZhETF 32, issue 1, 140 (1957).
29. Skanavi G. I. and Matveeva E. N., ZhETF 30, issue 6, 1047 (1956).
30. Konorova E. A. and Sorokina L. A., ZhETF 32, issue 1, 143 (1957).
31. Adirovich E. I. and Kolotilova V. G., DAN 105, 709 (1955).
32. Vavilov V. S., L. S. Smirnov et al., ZhETF 26, 1865 (1956).
33. Rzhanov A. V., ZhETF 26, 1389 (1956).
34. Vul B. M., ZhETF 26, 2403 (1956).

5. * From 1947 to 1954 the laboratory of oscillations was headed by M. A. Leontovich; at present it is directed by A. M. Prokhorov. ↩