PHYSICISTS—LAUREATES OF THE STALIN PRIZE

On the 10th Anniversary of the Establishment of the Stalin Prizes

V. V. Shepel

The Soviet government and the Central Committee of our Party devote enormous attention to the development of science in our country and show constant concern for scientists. The broad scope of scientific research in the USSR is conditioned by the very nature of the Soviet social system: the foundation for the development of our state is the highest achievement of science—the Marxist-Leninist doctrine. Only under the conditions of a socialist state can scientists create for the people, for its welfare and prosperity. The goal of serving the people, set before our scientists by the great luminary of science—Comrade Stalin—inspires them to new creative successes and calls forth a surge of creative forces.

A vivid manifestation of the Party’s and government’s concern for our scientists is the establishment, in commemoration of Comrade Stalin’s sixtieth birthday, of the Stalin Prizes for outstanding scientific works, inventions, and fundamental improvements in methods of production. Over the past 10 years, 28 scientific works in the field of the physical sciences and 30 inventions carried out by physicists have been awarded the Stalin Prize.

The Stalin Prizes have been awarded to the most outstanding investigations in the field of the structure of matter and cosmic rays.

Of greatest interest in this field is the work of A. I. Alikhanov and A. I. Alikhanyan, which led to the discovery of new particles—varitrons. As a result of the investigation of cosmic rays on Mount Aragats, at an altitude of 3250 m, with the aid of a special instrument they had constructed, called a magnetic mass spectrometer for cosmic rays, the Alikhanovs discovered in the composition of the radiation particles possessing various masses, including masses greater than that of the meson and even greater than that of the proton.

These investigations indisputably proved the presence, in the composition of cosmic rays at an altitude of 3250 m, of particles both negative and positive in charge, as well as

positive, with masses 200, 350, 500, 950, 3400, 8000, and 20,000 times greater than the mass of the electron, which were named barytrons.

The existence of barytrons, i.e. of an entire system of new particles, compels us to view many phenomena in cosmic rays in a new way and, in particular, changes our views on the nature of the hard component and on the mechanism of its origin.

Investigations have shown that in the hard component barytrons constitute a noticeable fraction, and that the conception of the hard component as homogeneous is incorrect. The supposition also arises that mesons of different masses appear as a result of the gradual transformation of heavy barytrons into lighter ones. The existence of barytrons also compels a reconsideration of views on the nature of nuclear forces. It is appropriate to recall in this connection that the discovery of a new type of elementary particles has always been an enormous event for physics, giving impetus to the discovery and development of new domains of physical knowledge.

A. I. Alikhanov and A. I. Alikhanyan were also awarded the Stalin Prize in 1941 for outstanding investigations on radioactivity.

In the field of cosmic rays, the Stalin Prizes this year have recognized the work of Prof. S. N. Vernov and, in 1946, the work of Prof. A. P. Zhdanov.

S. N. Vernov is a pioneer in the study of cosmic rays in the very upper layers of the atmosphere. The importance of such research follows from the fact that one of the most urgent and at the same time most difficult problems is the study of the nature and properties of the primary cosmic radiation entering the Earth’s atmosphere from the depths of cosmic space.

On the path toward studying these phenomena there are great experimental difficulties, since cosmic radiation, penetrating through the thickness of the atmosphere, undergoes transformations accompanied by a number of complex phenomena that have not yet been fully explained.

S. N. Vernov, together with a group of scientific workers, carried out on a broad scale a many-sided study of cosmic radiation in the upper layers of the atmosphere; for this purpose original apparatus was created, capable of operating under conditions of variable temperatures and of automatically transmitting readings to observers on the ground.

These works yielded very substantial and varied material on primary cosmic radiation. Thus, it was established that primary cosmic radiation causes “special” shower processes of an “explosive” character, the nature of which still remains unknown. A careful study of the “special” showers showed that electrons and photons are born in their composition—a phenomenon which, apparently, makes it possible to approach the disclosure of the source of the “soft” component of cosmic radiation predominating in the atmosphere. The question of the origin of this component until the most recent time

remained unclear. Later, S. N. Vernov studied the angular distribution of various components of cosmic radiation in the stratosphere. Analysis of these data leads to the conclusion that both positive and negative particles exist in the primary radiation.

Professor A. P. Zhdanov is responsible for a most interesting discovery of a new type of splitting of atomic nuclei, caused in some cases by cosmic rays.

In this work A. P. Zhdanov used a method, improved by him, of thick-layer photographic plates. This method was first proposed by the Leningrad physicist Prof. L. V. Mysovskii in 1927; subsequently it was developed by A. P. Zhdanov and at present is one of the most important experimental methods of nuclear physics.

In 1942 in Kazan, A. P. Zhdanov discovered on his plates a large number of traces of the action of cosmic rays. In these photographs by A. P. Zhdanov one can see how, from the nuclei of atoms—for example, the nuclei of silver and bromine (which are part of the photographic layer)—under the action of fast cosmic particles, a large number of particles fly out, equal to the number of protons in the given nucleus. A careful study of these photographs led A. P. Zhdanov to the conclusion that in his experiments there occurs a complete disintegration of atomic nuclei into their constituent particles under the action of cosmic rays.

A fundamental discovery in the field of nuclear physics belongs to the young Soviet physicists K. A. Petrzhak and G. N. Flerov. These scientists were the first to observe the spontaneous division of uranium nuclei. For this purpose they employed very bold techniques and developed a method that made it possible to observe the phenomenon itself and to estimate the order of magnitude of the half-life period. Petrzhak and Flerov used a special ionization chamber consisting of many plates, with a total surface area of about 1000 cm², coated with uranium oxide. The large surface was needed in order to observe the appearance of fragments in as large a quantity of uranium as possible.

The authors came to the conclusion that the time during which half of the uranium taken will spontaneously divide is equal to \(10^{14}—10^{15}\) years.

Last year Prof. G. D. Latyshev was awarded the Stalin Prize for experimental investigations in the physics of the atomic nucleus.

G. D. Latyshev and his coworkers developed a precise experimental technique that made it possible to discover new facts in the study of gamma rays.

The discovery made by G. D. Latyshev consists in the detection of so-called monoenergetic (monochromatic) positrons during the internal conversion of gamma rays. For the energy of positrons of internal conversion one usually obtains a continuous spectrum. Studying this spectrum, G. D. Latyshev discovered,

that sharp peaks, belonging to positrons with a definite energy, are superimposed on the ordinary continuous spectrum of positrons. This is explained by the fact that, in the case of internal conversion of gamma rays occurring in an atom in which electrons are absent from one of the shells, the electron formed during conversion is captured by one of these free shells, while the positron is emitted, carrying away a definite energy.

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A number of works in the field of optics have been awarded Stalin Prizes, including outstanding theoretical and experimental studies and important achievements in technical optics.

In tsarist Russia there was no optical industry, nor were there special optical institutes. Russia used chiefly imported optical instruments. In 1918 the State Optical Institute was founded, becoming a center of scientific research and scientific-technical work in the field of optics. Major works in optics were undertaken after the Great October Socialist Revolution also at the Physical Institute of the Academy of Sciences.

At the present time our country fully supplies itself with the most precise optical instruments and apparatus.

The works of a number of opticians have been awarded Stalin Prizes.

The President of the Academy of Sciences of the USSR, Academician S. I. Vavilov, has twice been awarded the Stalin Prize for scientific research in optics. Academician Vavilov’s scientific works relate chiefly to problems of physical optics, especially to the field of fluorescence. This branch of physics had been little studied, and Academician Vavilov, who has been engaged in the study of fluorescence for more than 20 years, is responsible for a large number of experimental and theoretical investigations in this field.

S. I. Vavilov established a law according to which the yield of fluorescence does not depend on wavelength. This law makes it possible to reveal the mechanism of excitation of a molecule under luminescence. It also finds practical application in laboratories for measuring the intensity of light, especially in the ultraviolet region of the spectrum. Furthermore, the phenomenon known as concentration quenching of fluorescence has long been known: beginning with a certain concentration, the brightness of fluorescence decreases with further increase in the concentration of the fluorescent substance. There had been no theory of this phenomenon. In his recent works Vavilov gave a theoretical solution to this question. He established the existence of two kinds of concentration quenching of fluorescence, distinct in their nature, in connection with the mechanisms—different in the two cases—of energy transfer from one molecule to another.

Of great importance are the works of S. I. Vavilov devoted to the study of the polarization of fluorescence in solutions. It turned out that the fluorescence light emitted by complex dye molecules exhibits a definite percentage of polarization. Vavilov further showed that this polarization depends substantially on the wavelength of the exciting light, and at certain wavelengths even changes its sign. The dependence of the degree of polarization of fluorescence on wavelength thus forms a spectrum that is extremely characteristic of the fluorescing molecule and makes it possible to judge the peculiarities of its structure.

Another cycle of S. I. Vavilov’s work is devoted to the visual observation of quantum fluctuations of light. In this field, as in the field of the study of fluorescence, Vavilov is fully a pioneer. It should be noted that the very idea of establishing and studying quantum fluctuations of energy by means of direct visual perception is highly remarkable and bold.

With the aid of an ingenious and refined methodology, and on the basis of extensive experimental material, the discontinuous nature of light was undoubtedly proved. These works on the visual observation of quantum fluctuations also provide a new method for measuring the absorption of light in the ocular media of the living eye, which is of great importance for physiological optics and the theory of vision.

For all these investigations S. I. Vavilov was awarded the Stalin Prize in 1943.

In 1946 S. I. Vavilov, together with his collaborators—Professors P. N. Cherenkov, I. E. Tamm, and I. M. Frank—was awarded the first prize in physics for the discovery and investigation of a new phenomenon—a special type of luminescence arising in liquids when electrons move in them with a velocity exceeding the phase velocity of light in the given medium.

The great fundamental interest of this discovery consists in the following. All previously known cases of luminescence were connected with accelerations of electrons, and it was believed that uniform motion of electrons is not accompanied by radiation. The aforementioned scientists proved the presence of radiation from uniformly moving electrons under special conditions.

The central point of the theory of such luminescence, developed by Vavilov, Tamm, and Frank, is the assertion that luminescence is emitted by electrons moving with a constant velocity exceeding the phase velocity of visible light in the given medium. The boldness of this idea becomes especially clear if one takes into account that, with the advent of the theory of relativity, motion at velocities exceeding the speed of light was regarded as impossible. But in this connection, as the authors pointed out, the circumstance had not been taken into account that in material media the motion of electrons with a velocity exceeding the phase velocity ...

of light in the given medium (but remaining less than the speed of light in vacuum, i.e., not contradicting the theory of relativity). At such speeds the uniform motion of electrons is accompanied by radiation, which was experimentally discovered by Cherenkov. The mechanism by which this glow arises is analogous to the mechanism by which an acoustic wave arises when there is motion in air at supersonic speed.

Of great interest are the works in optics of the Stalin Prize laureate, Corresponding Member of the Academy of Sciences of the USSR I. V. Obreimov. For many years I. V. Obreimov worked on questions of the methodology of accurately determining the refractive indices and dispersion of optical glasses. As a result of the investigations carried out, he developed an original and very sensitive method for determining these quantities. The method is based on the use of liquids whose refractive index is very close to that of the glass immersed in them (immersion liquids), and on the phenomenon of diffraction. It is known that even very slight changes in the refractive index of glasses in many cases make it necessary to recalculate optical systems, which in turn introduces a number of changes into the manufacture of optical parts. This greatly complicates production. The application of Obreimov’s method makes it possible to exercise control over the optical constants of glass already in the process of melting it. It became possible, when necessary, to introduce changes into the composition of optical glass during manufacture and in this way to obtain optical glass with exceptionally constant properties.

In subsequent years I. V. Obreimov proposed and implemented a whole series of new applications of his method for solving problems from other fields of physics and technology. In particular, his method is successfully used for studying diffusion processes, for the precise measurement of temperatures (since the refractive index depends on temperature), and for controlling the course of chemical reactions at high pressures.

Professor of the Leningrad Physico-Technical Institute E. F. Gross was awarded the Stalin Prize for scientific investigations of the molecular scattering of light and of the microstructure of liquids and crystals.

Soon after the discovery of combination scattering by the Soviet physicists L. I. Mandelstam and G. S. Landsberg, E. F. Gross studied scattering in amorphous bodies, fused quartz, and glass. This work not only showed for the first time the presence of combination scattering in amorphous bodies, but also had great importance for understanding the structure of glasses and of amorphous bodies in general.

The further work of E. F. Gross concerned the experimental proof of the existence of scattering from elastic thermal waves in solid and liquid bodies. Theoretically, the existence of such a

the effect had been predicted considerably earlier by Academician Mandelstam, as well as by Brillouin. Despite the exceptionally great experimental difficulties, E. F. Gross succeeded, with undoubtedness (and contrary to the assertions of certain foreign physicists), in demonstrating the existence of the effect. Thus E. F. Gross is responsible for the experimental establishment of a new effect.

Of great interest is the work of the president of the Armenian Academy of Sciences, V. A. Ambartsumian, awarded the Stalin Prize for the creation of a new theory of light scattering in turbid media. This work has not only important theoretical but also great applied significance, for example in the problem of underwater visibility, visibility in the presence of smoke or fog, the scattering of light in milk glasses, etc. The solution of this problem presents enormous difficulties, which were successfully overcome by the author.

In 1949, for important investigations in atmospheric optics, the Stalin Prize was awarded to Professor of the Zhukovsky Air Force Engineering Academy I. A. Khvostikov.

In the field of practical spectroscopy one should note the outstanding works of Academician G. S. Landsberg and of the group of his collaborators: S. L. Mandelstam, N. S. Sventitsky, L. M. Ivantsov, and V. F. Smirnov. G. S. Landsberg, together with his collaborators, was the first to develop a method for the broad application of spectral analysis to the needs of the Soviet metallurgical and metalworking industry. As a result of several years’ work, G. S. Landsberg succeeded in accomplishing a task of primary importance in the field of quality control of metallic alloys by means of spectral analysis. The cost of quantitative spectral analysis is approximately 7–10 times lower than that of chemical analysis, while the speed of spectral analysis is approximately 50 times greater than the speed of chemical analysis.

Important work was carried out by M. L. Veingerov, professor of the State Optical Institute. He developed an entirely new method of gas analysis; the method is based on the sounding of gases and vapors under the action of a stream of infrared rays interrupted at an acoustic frequency. With intermittent absorption of the radiation by the molecules, periodic heating and cooling of the gas occurs, which entails oscillations of its pressure, i.e., produces sound. The intensity of the sound depends on how strongly the infrared rays are absorbed by the gas. The sound is picked up by a microphone and produces a current; the current is amplified by a tube amplifier, rectified, and measured by a pointer galvanometer. The readings of the galvanometer are related to the composition of the gas mixture under investigation.

For rapid analysis of gas mixtures on this principle, optico-acoustic gas analyzers have been constructed; their further development is the spectrophone—an instrument intended for rapid quantitative analysis of multicomponent gas

mixtures, and also for the study of the infrared absorption spectra of gases.

E. M. Brumberg, a research worker at the State Optical Institute, developed and implemented a new, original method of microscopy by means of ultraviolet rays. The difficulty of studying many objects with a microscope (in particular, the overwhelming majority of biological objects) is due in many cases not so much to the insufficient resolving power of the microscope as to the insufficient contrast of the specimen in visible light. This deficiency, or complete absence of contrast, is caused by the absence in the specimen of absorption bands in the visible part of the spectrum. The same specimens, however, have strong absorption bands in the ultraviolet part of the spectrum. They therefore possess, invisible to the eye, a sharp and varied “coloration” in the ultraviolet. Proceeding from this, E. M. Brumberg first of all substantially improved ultraviolet microscopy by constructing a special reflecting objective. Further, by photographing the specimen at three wavelengths in the ultraviolet (with the aid of special filters developed by him), E. M. Brumberg then reproduces these photographs in conventional visible colors, thereby imparting rich contrast to the specimen.

Another method developed by Brumberg is a visual one. In the eyepiece of the ultraviolet microscope, in the plane of the real image of the specimen, a special fluorescent screen is placed, the fluorescence color of which depends sharply on the wavelength of the ultraviolet rays incident upon it. In view of the fact that the fluorescence color of pure substances does not depend on the wavelength of the exciting light, such a screen can be obtained only by mixing three fluorescent substances with fluorescence of the three primary colors and with selective absorption in the ultraviolet region. It is not difficult to see that on such a screen, when the specimen is illuminated simultaneously by the full ultraviolet spectrum (without a monochromator), we shall directly obtain color images similar to those obtained by means of color photography. The action of such a fluorescent screen has a close analogy with the action of the retina of the eye, which likewise analyzes the light flux incident upon it by means of three centers of color sensitivity.

The new method proposed by E. M. Brumberg is of the greatest interest for medicine, biology, botany, mineralogy, and metallography.

In concluding this brief survey of work in optics, let us note a number of outstanding inventions in the field of optical instrument construction. Among these are: the construction by Acad. V. P. Linnik of interferometers used for monitoring the accuracy of surface finishing; the creation by D. D. Maksutov of new types of aberrational-

optical systems (meniscus systems); the creation, by groups of scientific workers of the State Optical Institute—A. I. Tudorovskii, G. G. Slyusarev, Volosov, Yakhontov, and others—of new types of aerial photographic lenses, which are of great importance for aerial photographic reconnaissance; the creation, by Academician A. A. Lebedev, V. N. Verner, and N. G. Zandin, of a domestically produced electron microscope, possessing a number of advantages over other known models.

In the field of radiophysics, Stalin Prizes were awarded to the works of Academicians L. I. Mandelstam and N. D. Papaleksi on questions of the theory of oscillations and the propagation of radio waves.

The propagation of radio waves over the surface of the Earth is one of the fundamental problems of radio engineering. However, despite all the importance of this problem, it had been very little developed. The reason for this, above all, was the absence of reliable experimental methods for investigating the central point of the whole problem—namely, the question of the velocity of propagation of radio waves over the surface of the Earth.

L. I. Mandelstam and N. D. Papaleksi proposed an original and precise method for the experimental study of radio-wave propagation—namely, the radio-interferometric method. This method made it possible, first of all, to clarify the question of the influence of the Earth on the velocity of propagation of radio waves. Numerous and precise experiments carried out under the direction of L. I. Mandelstam and N. D. Papaleksi gave an exhaustive answer to this question. The results they obtained made it necessary to abandon certain notions that had formerly been generally accepted.

At the same time, the results of the investigations of L. I. Mandelstam and N. D. Papaleksi enabled them to solve an important practical problem: the use of radio waves for measuring distances between two points on the surface of the Earth. For this purpose L. I. Mandelstam and N. D. Papaleksi applied the same radio-interferometric method. Under their direction, a radio rangefinder was developed.

A second work in the field of radiophysics awarded a Stalin Prize is the work of Academician V. A. Fock, “Diffraction of Radio Waves around the Earth’s Surface.” This work sums up V. A. Fock’s investigations on the theory of the propagation of radio waves near the Earth’s surface. They led to the clarification and completion of the theory of the “ground ray” and to the establishment of correct modern views on the propagation of waves near a flat Earth. However, the practical problems of radio engineering require that the curvature of the Earth be taken into account. Only Academician V. A. Fock succeeded in giving a complete and exhaustive solution of this problem in the work “Diffraction of Radio Waves around the Earth’s Surface.”

PHYSICISTS—LAUREATES OF THE STALIN PRIZE

For works in the physics of semiconductors and dielectrics, Stalin Prizes have been awarded to Academician A. F. Ioffe, Corresponding Member of the Academy of Sciences B. M. Vul, and also Corresponding Member A. V. Shubnikov.

Academician A. F. Ioffe is the founder and head of a scientific school in the field of semiconductors and dielectrics.

Combining theoretical research with technical applications, Acad. A. F. Ioffe and his collaborators succeeded in solving a number of most important problems. The general theory of the properties of semiconductors, developed as a result of studying the mechanism of conductivity, the photoelectric effect, contact potentials, and thermoelectromotive forces of an enormous number of semiconductors, made it possible to find ways of controlling the properties of semiconductors.

Academician A. F. Ioffe, or under his direction, developed: thallium-sulfide photocells with a blocking layer, which have found wide application in the motion-picture industry and other fields of automation; powerful rectifiers made of copper sulfide (sulfide rectifiers) for electric-welding apparatus; non-aging selenium rectifiers, etc.

In the field of theory, the mechanism of electrical conductivity and of the influence of impurities introduced into a semiconductor was clarified; the mechanism of phenomena at the boundary between semiconductors, determining rectification and the photoelectric effect in photocells with a blocking layer, was clarified. A detailed theory was created of current fluctuations in semiconductors, which lead to the appearance of interference and “noise”; the thermoelectric properties of a number of semiconductors were studied, and powerful thermoelements were created for the first time.

Of great interest are also the prize-winning works of Prof. B. M. Vul. He discovered new substances with high and ultrahigh dielectric permittivity. Dielectric permittivity, like every property of a substance, depends on its structure. Over the last decades the study of dielectric permittivity has acquired major practical significance, owing to the wide use of electrical-insulating materials. The development of electrical engineering and, in particular, radio engineering has posed the task of creating materials possessing special properties, in particular high dielectric permittivity.

The electrically insulating materials practically used until recently possess dielectric permittivity measured in a few units, and only in recent years has it been possible to introduce into practice materials whose dielectric permittivity amounts to several tens.

A considerable merit in the development of such materials and in introducing them into production belongs to B. M. Vul, who discovered that

barium titanate has an extremely high dielectric permittivity, reaching 2000 at room temperature.

B. M. Vul and his coworkers have studied the dependence of the dielectric permittivity of barium titanate on temperature over a wide range, including temperatures close to absolute zero; on pressure, up to 2000 atmospheres; and on the field strength and frequency of the applied electric field. Dielectric hysteresis, analogous to magnetic hysteresis in iron, has been found; it has been shown that barium titanate is a new type of the still very rare substances possessing spontaneous electric polarization and called Rochelle-salt—or ferroelectrics. Until now four ferroelectrics were known, of which Rochelle salt possesses spontaneous polarization only in the temperature interval from \(-20\) to \(+25^\circ\)C, while the other three do so only at temperatures below \(-150^\circ\)C. Barium titanate possesses spontaneous polarization over the entire temperature range below \(+80^\circ\)C. This property of barium titanate, in combination with its chemical stability, which distinguishes it from the previously known ferroelectrics, as well as the simple method of obtaining it, for the first time opens up the possibility of creating a new class of materials which, by their dielectric properties, are destined to occupy the same place among electrical insulating materials as iron, by its magnetic properties, occupies among metals.

Corresponding Member of the Academy of Sciences of the USSR A. V. Shubnikov has been awarded the title of Stalin Prize laureate for the discovery and investigation of a new type of piezoelectric. It is known that piezoelectrics are substances on whose surfaces charges appear under deformation. These include crystals of quartz, tourmaline, Rochelle salt, and others. Piezoelectric cells made from such crystals usually have small dimensions, which limits the range of their application. On the basis of theoretical investigations A. V. Shubnikov established the possibility of obtaining nonpolar piezoelectric textures. As is known, a texture is the preferential orientation of crystals in a polycrystalline aggregate. For the practical realization of these textures A. V. Shubnikov chose Rochelle salt. Upon rapid cooling of a melt, Rochelle salt forms a strong polycrystalline mass consisting of needle-like crystals. Owing to these properties, in order to obtain piezoelectric textures it proved possible to apply and work out in detail a simple method for orienting microscopic crystals. For this purpose the melt of Rochelle salt is applied to the surface of a solid body with the aid of an ordinary brush, in rectilinear strokes in one or in two opposite directions. The artificial piezoelectric made from Rochelle salt is a translucent porcelain-like mass, easily worked with a cutter, sandpaper, file, and so on. From it piezoelements can be made in the form of plates

of any thickness, and also in the form of articles of the most varied shape and size. If the texture is applied to the surface of a metallic object, then the latter itself can serve as one electrode of the element; the other electrode may be a metal foil or mesh glued to the free surface of the texture. Possessing a piezoelectric effect greater than that of quartz, the Rochelle-salt texture may find application in the most diverse fields of science and technology. Any mechanical vibrations can be converted, by means of a textured piezoelectric element, into electrical vibrations, which can be observed and recorded with the aid of appropriate electrical instruments.

On the other hand, an alternating electric voltage applied to the textured element causes in it, by virtue of the existence of the inverse piezoelectric effect, mechanical vibration. Hence the application of piezoelectric textures for obtaining ultrasounds and infrasounds suggests itself naturally—quite powerful ones, since the dimensions of the piezoelements can be very large.

Stalin Prizes were also awarded to a number of outstanding works in the field of molecular physics.

First of all, one should note the outstanding investigations of Soviet physicists in the field of low-temperature physics, carried out at the Institute of Physical Problems of the Academy of Sciences of the USSR.

Academician P. L. Kapitsa discovered and investigated new phenomena—the phenomena of superfluidity of liquid helium. He showed that helium II is a liquid possessing no viscosity, and, by analogy with the superconductivity of metals, called this property superfluidity. In the phenomenon of superconductivity we encounter the case where the carriers of electricity—electrons—can flow without resistance through the crystal lattice. In superfluidity we have atoms which can likewise move without friction in a definite direction relative to one another. Investigations showed that the viscosity of helium II does not exceed \(10^{-9}\) poise, i.e. it is 10 thousand times less than the viscosity of hydrogen in the gaseous state and ten million times less than the viscosity of water. It had already been known earlier that helium II in capillaries possesses an anomalously large thermal conductivity—approximately a million times greater than the thermal conductivity of copper. P. L. Kapitsa showed that the anomalously large thermal conductivity of helium II is due to its superfluidity. The high heat transfer in helium II is explained by quite peculiar convective flows not characteristic of other liquids.

A detailed investigation of the superfluidity of helium II yielded rich experimental material, on the basis of which Academician L. D. Lan-

to develop a rigorous quantitative theory of this phenomenon. This work of L. D. Landau, like his work on the theory of superconductivity, was the culmination of his scientific investigations of phase transitions of the second kind, for which he was awarded the title of Stalin Prize laureate.

In contrast to phase transitions of the first kind—for example, the transition of water from the liquid state to the solid, or the transition of sulfur from rhombic to monoclinic—in which at the point of phase transition both states of the substance exist, in phase transitions of the second kind the substance is found in only one state. In phase transitions of the second kind there is a jump in heat capacity, the coefficient of thermal expansion, and the like, i.e., in the first derivatives of thermodynamic quantities.

The methods developed by L. D. Landau make it possible to determine the possibility of the existence of a phase transition of the second kind in particular concrete cases.

In his works on superconductivity, L. D. Landau gave a picture of the physical essence of the so-called intermediate state and developed its quantitative theory.

The greatest physicists working in the field of superconductivity did not succeed in detecting the lamellar structure experimentally, and only in the experiments of Prof. A. I. Shalnikov, thanks to an exceptionally delicate experiment, was it possible to observe it in the most direct way. A. I. Shalnikov put forward the assumption that at the surface of a narrow slit in a superconducting sphere the lamellar structure would not be expressed as strongly as at the outer surfaces of the superconductor, and consequently, by developing a micromethod for measuring magnetic fields in this slit, it would be possible directly to observe the inhomogeneities of the field caused by the lamellar structure.

Such an original micromethod for measuring the field was developed by Shalnikov. An idea of the difficulty of developing such a method may be obtained from the fact that the measuring device had to make it possible to measure the field in a gap of the order of 25 microns with a measuring device length of about 0.7 millimeter. With the aid of such a micromeasuring device, which could be moved in the slit of the superconducting sphere, A. I. Shalnikov discovered the existence of layers in the intermediate state, discovered the origination of the lamellar structure and its disappearance when the specimen was brought into the superconducting state by changing the temperature or changing the magnetic field.

The theory of the superfluidity of helium II, developed by L. D. Landau, led to the conclusion that helium II consists of two parts: “normal” and “superfluid.” From this it followed that in helium II there must exist two different velocities of sound. Doctor of Physico-Mathematical Sciences V. P. Peshkov discovered and comprehensively studied this new phenomenon—the so-called “second sound.”

According to V. P. Peshkov’s data, the velocity of second sound in helium II at \(1.32^\circ\) K is \(19.2\) m/sec, and at \(1.70^\circ\) K it is \(20.00\) m/sec, which gives good agreement with theory. The velocity of ordinary sound in helium II is about \(240\) m/sec. V. P. Peshkov’s investigations, awarded the Stalin Prize, most convincingly prove the existence in helium II of two liquids: an ordinary one and a superfluid one.

Of great interest are the works of Prof. N. N. Bogolyubov on statistical physics, summarized in the work Problems of Dynamical Theory in Statistical Physics.

In these works, concerning the derivation of kinetic equations and equations of thermodynamic statistics with account taken of the interaction of particles, N. N. Bogolyubov for the first time obtained kinetic equations on the basis of the mechanics of an ensemble of molecules, both for classical and for quantum systems. Various forms of these equations were established, having extensive applications in problems of statistical physics.

In the field of the study of solid-state physics, for the outstanding results achieved the Stalin Prize was awarded to the professors of Tomsk State University V. D. Kuznetsov and M. A. Bolshanina. Their works are summarized in the major three-volume work Physics of the Solid State.

Neither in Soviet nor in foreign literature on solid-state physics is there another such book in which the science of the plasticity and strength of crystalline solids, chiefly metals, is presented in such detail, scientifically and at the same time accessibly.

The book is permeated by a single idea and represents a synthesis of the enormous experimental and theoretical material accumulated by the authors over many years.

In the field of metal physics, the Stalin Prize was awarded to Prof. G. V. Kurdyumov for his investigations of martensitic transformations in alloys.

These works of G. V. Kurdyumov sum up twenty years of work by the author and the school he heads on the study of martensitic transformation in steel and other alloys. They give a profound theoretical analysis of the regularities of this process established by the author and set forth original conceptions of its nature.

The great interest shown by metallurgists in the question of the nature of the transformation of austenite into martensite is explained above all by the fact that this transformation lies at the basis of the hardening of steel. A number of phenomena accompanying the transformation of austenite into martensite forced one to think that this transformation represents a special process, not connected with the formation of nuclei and their subsequent growth. It was considered that the process of transformation of austenite into martensite is an athermal phenomenon and rather a purely mechanical one.

The investigations carried out by G. V. Kurdyumov led to fundamental changes in conceptions of the nature of these transformations. G. V. Kurdyumov and his coworkers made a very important discovery

“reversibility” of martensitic transformations. The microphotographs showed with great persuasiveness how, as the temperature is lowered, martensite needles grow, and how, as it is raised, they gradually disappear. Further, G. V. Kurdyumov showed that the established view of martensitic transformations in steels as proceeding instantaneously and independently of temperature is incorrect. In fact, already at temperatures of \(-50^\circ\) C the rate of transformation becomes measurable, decreasing sharply with further lowering of the temperature. At temperatures below \(-100^\circ\) C the isothermal transformation of austenite into martensite can be observed for hours.

The numerous experimental investigations of G. V. Kurdyumov in the field of martensitic transformations led him to create a new physical theory of these transformations: this theory regards martensitic transformations as phase transformations in a one-component system, similar to allotropic transformations in pure substances. From the new point of view, martensitic phases are regarded as low-temperature crystalline modifications of a solid solution, requiring the formation of nuclei and their growth.

The significance of G. V. Kurdyumov’s work is clear from the fact that it makes it possible to approach in a new way the technology of hardening and tempering steel and the methods of heat treatment (especially the so-called “cold treatment of steel”).

For scientific investigations on the theory of the liquid state, summarized in the monograph Kinetic Theory of Liquids (1945), the Stalin Prize was awarded to Corresponding Member of the Academy of Sciences Prof. Ya. I. Frenkel.

Prof. Ya. I. Frenkel’s book Kinetic Theory of Liquids is a compendium of all the author’s work in this field over a period of more than twenty years. The main idea of the book consists in considering thermal motion in solids and liquids.

The study of real crystals made it necessary to abandon the simplified conception of them as ideal crystalline lattices. Ya. I. Frenkel’s ideas helped to construct the theory of diffusion, electrical conductivity, and melting. Ya. I. Frenkel discovered in solids many properties that bring them closer to liquids.

Many physicists have been awarded the prize named after Comrade Stalin for outstanding inventions that played a major role in the defense of the country and in strengthening its economic might. Prof. A. P. Aleksandrov, V. R. Regel, and others were awarded the prize for the invention of a method for protecting ships; Prof. A. A. Gershun—for an invention in the field of camouflage; N. D. Smirnov, K. S. Vul’fson, V. L. Granovskii—for the invention of a new type of heat direction finder; Prof. S. Ya. Sokolov—for the invention of a method of ultrasonic flaw detection; Prof. P. V. Timofeev and his co-workers—for the creation of optical instruments; Prof. N. S. Akulov—for the application of the theory of ferromagnetism developed by him to the flaw detection of metals; Prof. T. P. Kravets and his co-workers—for

for the development of a new system and instruments for determining the sensitivity of photoemulsions; the research workers N. A. Tolstoy and P. P. Feofilov—for the creation of an instrument for studying rapidly occurring physical processes, and others.

In the present article the works of Stalin Prize laureates in the field of physics have been briefly reviewed. These works demonstrate the high level of Soviet science, capable of solving any scientific problems. Alongside the laureates there labors a vast army of Soviet scientists, engineers, technicians, and inventors, devoting their strength and knowledge to the great cause of building communism.

Never in the entire history of mankind has science played such an important role in the life of society as it does among us, in the country of victorious socialism. Only in a socialist state have the dreams of many great men of science come true—to create for the people, for their welfare and prosperity.

Any major tasks set before our scientists by the Bolshevik Party and the Soviet Government are successfully solved because unlimited possibilities for the development of science have been created in our country; because Soviet scientists are devoted to the cause of the Party; because they are an inseparable part of the Soviet people, its army of thought, its army of knowledge.