by Tatyana ROGANOVA, Dr. Sc. (Phys. & Math.), Head of the Laboratory of the Research Institute of Nuclear Physics named after D. Skobeltsyn, Lomonosov Moscow State University

July 11, 2010, is a day of the 100th birthday of a prominent Russian physicist Academician Sergei Vernov (1910-1982). His name is inseparable from the studies of almost all aspects of cosmic rays and the theory of elementary particles, plasma phenomena, astrophysics and geophysics.

BEGINNING

Sergei Vernov was born on July 11, 1910, in the town of Sestroretsk, Leningrad Region. His father was a post office clerk, mother taught maths. In 1926, Vernov graduated from the Unified Labor School in Leningrad. There is a record in the protocol of the Examination Board that he "has big potential both in mathematics and in the humanities" and was "acknowledged by all teachers as the best student of the final class". That very year he entered Mechanical School and a year later became a student of the Department of Physics and Mathematics at the Leningrad Polytechnical Institute.

Concurrently with studies, Vernov worked at the Institute of Radium, which predetermined his future life: in 1931, after graduation, Vernov became a post-graduate student of a nuclear research center, where he started activities connected with studies of cosmic rays, to which he dedicated his whole life.

"FLYING LABORATORY"

In early 1930s, there was almost no information on cosmic rays. Scientists only knew that they represent a complex mixture of extremely high-energy particles (as compared with radiation of radioactive substances). It was assumed that the major part of cosmic rays formed in the atmosphere under the effect of a certain primary component. Moreover, very few foreign experiments with a simple device-ionization chamber-showed: intensity of cosmic rays increases with the altitude.

Vernov tried to minimize the effect of the atmosphere on the primary component in order to get closer to the understanding of its nature; he established the first in the world "flying laboratory" furnished with equipment for automatic altitude measurements of cosmic rays to be transmitted to the Earth over the radio. He used the idea of a stratospheric radio-sounding apparatus, designed by the famous Soviet radiologist professor Pavel Molchanov from Leningrad, which was launched for the first time in 1930. Results obtained by Sergei Vernov due to this method formed a basis for his thesis for degree of candidate. The main thing was that radio enabled to keep the equipment "safe", which opened up new opportunities in the field of experimental activity, i.e. experiments could be carried out in any region of the country, in the mountains and in the ocean.

In 1935, Vernov started work for degree of doctor at the USSR AS Institute of Physics named after P. Le-bedev (FIAN): by that time he had moved from Leningrad to Moscow. There, headed by Academician Sergei Vavilov, founder of the Soviet scientific school of physical optics, President of the USSR AS in 1945-1951, and a well-known expert in high-energy physics Academician Dmitry Skobeltsyn*, Vernov "polished" his style that combined challenging experiments and deep theoretical analysis.

In 1936-1938, Sergei Vernov studied latitudinal effect of cosmic rays in stratosphere in Leningrad, Yerevan and near the equator, organized a marine expedition to the Indian Ocean to launch sounding balloons. The achieved results exceeded all expectations: density of cosmic particles near the equator is approximately 4 times less as compared with high latitudes; they are not neutral but have an electric charge, which results in their deflection by the Earth's magnetic field. In 1939

* See: M. Panasyuk, Ye. Romanovsky, "From Hypotheses to Discoveries", Science in Russia, No. 6, 1995.-Ed.

Vernov defended his thesis for degree of doctor-the first one on this subject at the Institute of Physics.

ASSAULTING THE STRATOSPHERE

In 1943, Vernov began to work full time at Lomonosov Moscow State University. First at the Department of Atomic Nucleus and Radioactive Radiations and then at the Research Institute of Nuclear Physics set up at the Moscow State University in 1946, where he soon became Deputy Director for scientific work and resumed broad-scale stratosphere studies interrupted by the Great Patriotic War.

Starting from 1944, Eastern Pamir served as an Alpine proving ground for studies of cosmic radiation. FIAN employees organized the first expedition there. By win-ter 1947, there was constructed a big modern building of a scientific station intended for all-year-round opera-tion in the Chechekty canyon. It was there that scientists made significant discoveries that shed light on the nature of electron-nuclear showers and a nuclear-cascade process. But many things were still unknown.

Thus, in the 1940s, specialists believed that cosmic rays consisted of electrons and positrons. Vernov actively sup-ported this hypothesis as it explained high-altitude vari-ations, latitudinal effect and absence of azimuthal asym-metry near the equator that was proved, in particular, by the experiment of American physicists Thomas John and John Barry in 1939. But there also existed other points of view. For example, astrophysicist Mark Shane (USA) insisted that there were no high-energy electrons in cos-mic rays. In order to find a decisive answer to the ques-tion of the charge, Vernov in 1944 organized the second marine expedition to the equatorial latitudes of the Indian Ocean on the research vessel "Vityaz". The experiments carried out there proved that the data of some authors on the absence of the so-called east-west asymmetry were incorrect. In fact, it exists, and particles of cosmic rays are positively charged. It proved their pro-ton nature and became decisive for Vernov.

Further analysis of experiments under ≤10¹²eV enabled Vernov to obtain basic characteristics of interactions between cosmic rays and nuclei of air atoms, and led him to an important conclusion: in the processes of formation of pions* and splitting target nuclei into lighter fragments (protons, neutrons, alpha-particles), primary proton loses its energy only partially keeping, as Vernov used to say, "the lion's share" for itself. This unspent "energy" is taken away by one (leading) nucleone. Thus, he learned the nature of primary cosmic rays and main peculiarities of generation by them of secondary particles. The multi-year work conducted by the scientist had been widely acknowledged: in 1949 Vernov was awarded USSR State Prize and in 1953 he was elected Corresponding Member of the USSR Academy of Sciences.

* Pions-a group of particles of unstable hedrons.-Ed.

GIANT AIR SHOWERS

In late 1950s, Sergei Vernov designed a unique ShAL unit at the Moscow State University. For that time its measuring system occupied a huge area (about 3 km") and made it possible to register and study extensive air showers (hence the name), caused by superhigh-energy particles (5 • 10^l4-10¹⁷ eV). Measuring the energy spec-trum of primary cosmic rays in the said range, Vernov and his fellow employees found a break (at ~10¹⁵ eV) that most likely marked a transfer from the particles of galactic origin to more energetic ones coming from Metagalaxy. This result was registered as a scientific dis-covery confirmed in other experiments. However, its physical interpretation is still under question.

ShAL, made at the Moscow State University, was one of the most informative scientific units in the world. It was constantly updated, increasing its dimensions and number of measuring instruments. In addition to gas-discharge counters, they began to use scintillation and Cherenkov detectors*.

In search of the answer to the question of origin of high-energy cosmic rays and identification of their sources, in early 1970s scientists constructed one more big unit in the Lena River valley, 50 km away from Yakutsk, to register extensive air showers. It occupied an area of 20 km² and allowed to measure the primary energy spectrum under energies of up to 10²⁰ eV. This com-plex is still operating. Measurement of the angular dis-tribution of sources in galactic coordinates is one of the many "famous" results received here recently. Thus, it was established that an excess of extremely high-energy cosmic rays coincides with a plane of Hypergalaxy These data were also confirmed by experiments con-ducted on a 3,000 km² gigantic unit named after Pierre Auger located in Argentina.

Creation of technical devices to register extensive air showers through the Cherenkov light turned out to be a promising enterprise. In early 1990s, in Tunkinskaya Valley in Buryatia, 50 km away from Lake Baikal, there was launched Tunka-25 unit equipped with 25 integral detectors; it is used to measure the mass composition of primary cosmic rays in the energy range of 10¹⁵-10¹⁸ eV Tunka-133 unit furnished with 133 detectors was com-missioned in September 2009. Its area is 10 times as large as the area of its predecessor and it is able to regis-ter over 300 events with the energy exceeding 10¹⁷eV for a year of operation. Thus, the discovery made with ShAL unit laid foundation for a new fundamental ten-dency that has become fundamental in the astrophysics of cosmic rays.

IONIZATION CALORIMETERS

Sergei Vernov was always committed to non-trivial methods in science. In 1957, his colleagues Naum Grigorov, Vladimir Murzin and Ilya Rapoport presented the first in the world ionization calorimeter to register charged superhigh-energy particles and measure their

* Cherenkov detector-a special unit that registers radiation discov-ered in 1934 by the physicist Pavel Chevenkov, Nobel prizewinner in 1958. It occurs when a charged particle is moving in a transparent medium with a speed exceeding the speed of propagation of light in it. Cherenkov radiation (or Cherenkov light) is widely used in high-energy physics to register relativistic particles and measure their speed.-Ed.

spectra (today such devices make part of almost all units studying cosmic rays and accelerators). In 1965-1968, it was successfully tested in space at the time of launching four heavy satellites of Proton* series. Such equipment (over 101) had never been launched into orbit before. All devices were designed and manufactured in a very short period of time, which required enormous efforts of the Research Institute of Nuclear Physics, Moscow State University, which possessed a huge potential in this field. Vernov, Director of the institute at that time (from 1960), used all available financial and intellectual resources to accomplish this work. Satellites collected data on the spectrum of particles with energy of up to 10¹⁵ eV and dependence of proton-proton interaction section at the energy of up to 10¹¹ - 10¹⁵ eV, which are still often mentioned in scientific literature. Moreover, these mechanisms have produced a unique result, even though it is not yet proved or refuted, on the abrupt bend of the spectrum of protons at the energy of ~2 • 10¹² eV. Later on, in 1984-1986, scientists conducted measurements of the spectrum of protons, helium nuclei and heavier nuclei in the range of energies from 2 to 100 TeV on Sokol-1 and Sokol-2 satellites. These achievements have become possible thanks to Vernov too.

"COSMOPHYSICAL" PHENOMENON

It is worth pointing out that Sergei Vernov strived to carry out experiments at the highest altitudes possible by all available technical means. In 1946, he formed a spe-cial group at the FIAN and managed to contact Sergei Korolev** who headed the cosmic program. As a result, first rockets launched from Kapustin Yar proving ground to the altitudes of 70 and 100 km carried the equipment for studies of cosmic rays beyond the atmosphere. Flights of vertical rockets to the altitudes of 100-150 km lasted not more than 10-15 minutes.

Alexander Chudakov (Academician from 1987), who participated in all these experiments, recollected: "Only highly purposeful style of work may explain the fact that in the period from 1947 to 1951 Vernov's small group could take part in ten successful rocket launches, having designed a special telemetering equipment to transmit and receive big volumes of information for a short flight, and solved numerous technical difficulties of placing and exploitation of gas-discharge counters, impulse and integrating ionization chambers with relevant electron-ics on board."

Vernov had surprising intuition. Soon after the first experiment in 1947, he made a conclusion that lifetime of particles splitting into electrons or photons must be less than 10^-9 sec. It should be mentioned that it was the year of the discovery of π^±-mesons and at least 4 years prior to the discovery of l°-mesons in the accelerator. But, unfortunately, "cosmophysical" results were not published in due time and in 1952 works were terminat-ed even though, as Chudakov said, "Sergei Nikolaevich was always instinctively sure that they were very impor-tant and had great future ahead." Nevertheless, in 1958, these works were briefly mentioned at the Second Conference on Peaceful Use of Atomic Energy in Geneva.

Intensive studies of radiation beyond the atmosphere coincided with the beginning of space era-launching of the first artificial satellite of the Earth on October 4, 1957***. As you know, it did not carry any scientific equip-ment on board. At that time Vernov was fully taken by ground and stratosphere studies, launching of a big ShAL unit at the Moscow State University, other pro-

* See: Yu. Markov, "Baikonur: 50 Years of Serving Mankind", Science in Russia, No. 2, 2005.-Ed.

** See: N. Koroleva, "His Name and Cosmos Are Inseparable", Science in Russia, No. 1, 2007.-Ed.

*** See: B. Chertok, "The First Artificial Satellite", Science in Russia, No. 5, 2007.-Ed.

jects. Eyewitnesses recollected that he, as a majority of people, was astonished by this unexpected event.

But his reaction was immediate: he understood very well prospects of studies conducted with such equipment and at once contacted Korolev persuading him to install two gas-discharge counters on the second already fully equipped satellite. Scientists had only 2 weeks before November 3, 1957 (date of launching) and counters were "tuned" already on the proving ground. Nevertheless, during the flight all gear operated in a normal mode and ensured necessary measurements, but could not "catch on" radiation belts of the Earth. According to Chudakov, "The main reason lay in the fact that the data obtained by the equipment was transmitted in the form of short "sessions" when flying over the USSR territory, while information from the zone of the equator and Southern hemisphere was not available. Moreover, the counters were screened by means of a thick substance and poorly could hardly sense small-energy electron flows in the polar area."

As a result, the first observation of the zone of high intensity (radiation belt) was carried out by American astrophysicist Van Allen in February-March 1958 during flights of American artificial satellites of the Earth Explorer-1 and Explorer-3. Soviet scientists could get information on the streams of particles over different parts of our planet, including Southern hemisphere, only with the launch of the third Soviet satellite on May 15, 1958. It carried a multi-purpose device of a new type designed on the basis of a scintillation counter, high sensitive of which to X-ray quanta with the energy of 30 keV made it possi-ble to find an external radiation belt of the Earth*. This discovery was registered in the State Register in 1960, and Vernov and Chudakov were awarded Lenin Prize.

Cosmophysical research works headed by Sergei Vernov till the end of his life produced both scientific and practical results. In 1968, he was elected Member of the USSR Academy of Sciences.

The scientist paid much attention to experiments at automatic interplanetary stations moving towards the Moon, Mars and Venus. So, in 1959, the gear installed on such stations showed that the Moon had no radiation belts, in 1967 scientists received information on their absence on the Venus, and only in 1971 small radiation variations were registered near the Mars.

In many cases experimental studies of space had an applied character. For example, during the flight of Elektron-1 satellite (1964), due to a powerful radiation, solar batteries soon lost a capacity to produce electric energy. Then scientists began to study effects of radiation and other factors on materials, elements, assemblies of space equipment and living organisms. This laid a foun-dation for space dosimetry, established by Vernov, who organized a material science group to develop an applied direction of this discipline at our institute.

For fifty years of active creative work, Vernov organized a vast scientific school. His associates and fellow employees highly appreciated his ability not to follow traditional ways and see new horizons, focus spiritual and material efforts on the most important things. This often resulted in a discovery of major scientific trends and in a solution of significant state goals. Among his apprentices are laureates of Lenin, State and Lomonosov prizes. He "brought up" over 20 doctors and more than 60 candi-dates of sciences. Many of them have already established their own scientific schools and trends.

* See: M. Panasyuk, "Breakthrough Into Outer Space", Science in Russia, No. 4, 2000.-Ed.