Seminar

In the memory of Yury S.Zamyatnin

On 15 January, Ivan Ruskov (Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences, JINR) delivered a lecture on "Neutron-nuclear data for RDS" at the seminar of the Department of Nuclear Physics of FLNP. He dedicated this lecture to the 104th anniversary of the birth of one of the outstanding experimental physicists, Doctor of Physical and Mathematical Sciences Yury S.Zamyatnin (1.01.1921 - 24.03.2008), in whose group he worked for ten years.

Yury S.Zamyatnin is a winner of the Stalin Prize (1953) for research in the field of nuclear physics related to the development and testing of the RDS-6s product, and of the Lenin Prize (1962). For research and the organization of a number of scientific areas for meeting tasks during the implementation of the USSR Atomic Project, he was awarded four Orders of the Red Banner of Labor. He worked at JINR since 1976 - first at FLNR, later, since 1984 - at FLNP.

At the beginning of his speech, I.Ruskov proposed organizing an information and discussion seminar dedicated to current tasks, problems, research in the field of neutron nuclear physics. Taking into account the opinion of Yury Zamyatnin on the importance of such seminars for investigations and their contribution to science, they should be called "Zamyatninki".

The speaker started his story about the history of the Atomic Project by mentioning its main executors - Academicians of the USSR Academy of Sciences G.N.Flerov and I.M.Frank, Corresponding Member M.G.Meshcheryakov and of course, the well-known key figures of the project.

Yury Zamyatin entered the Physics Department of Moscow State University in 1938. His course consisted of such smart students as A.D.Sakharov, E.I.Zababakhin, F.L.Shapiro, M.I.Podgoretsky, B.G.Erozolimsky that studied with him. During the war, having interrupted his studies, Yury Zamyatin worked as a draftsman-designer at a military plant during the evacuation. Returning to Moscow in 1944, he passed the exams for the fourth and fifth years of the university as an external student and became a student of a special course that trained the first group of nuclear physicists in 1945. While still a student, he started working at Laboratory No.2 of the USSR Academy of Sciences (later, Laboratory of Measuring Instruments of the USSR Academy of Sciences, National Research Centre "Kurchatov Institute").

The first turn in his fate occurred in 1948, when the Laboratory Directorate offered him to go to Arzamas-16 as a member of G.N.Flerov's group. He was to work in KB-11 (later, VNIIEF, Sarov), whose scientific leader was Yu.B.Khariton. The business trip lasted for 18 years. Having arrived in Arzamas as a junior researcher, three years later, Yury Zamyatin was already heading the department. And in the last years of his work in Arzamas, he was the scientific leader of a 500-member staff. From 1948 to 1966, under the supervision of Yu.B.Khariton, he was engaged in the tasks related to the implementation of the Soviet Atomic Project; he participated in estimating the critical mass of metallic plutonium in charges of atomic and hydrogen bombs.

D.V.Shirkov, Yu.S.Zamyatnin and E.K.Bonyushkin (RFNC, Arzamas-16). 1995. Photo by Yury Tumanov

Yury Zamyatin initiated the development and implementation of high-frequency linear accelerators into physical research practice. The pulsed mode of the accelerator allowed for measurements of neutron cross-sections using the time-of-flight technique and obtaining numerous nuclear-physical data. He supervised the first research in KB-11 on measuring the fission cross-sections of uranium-235 and plutonium-239 with thermal neutrons. In 1954-1955, together with his colleagues, he carried out rather delicate experiments on measuring the spectra and angular distributions of neutrons from the fission of uranium-235 with neutrons with an energy of 14 MeV at different angles to the direction of the scattering of fission fragments.

One of the major research areas at KB-11 in the mid-1950s was the investigation of gas-dynamic thermonuclear fusion (GDTF). It turned out that new measuring equipment was required that would be highly effective in registering relatively small neutron yields. In the first explosive experiment on GDTF, a new technique of registering small neutron yields proposed by Yu.S.Zamyatin and V.M.Gorbachev was used for the first time - the technique of protracted registration. It was based on the use of the effect of slowing down fast thermonuclear neutrons in a hydrogen-containing moderator and registering gamma quanta produced during the capture of slowed neutrons by hydrogen nuclei. With the help of this technique, quantitative results were obtained for the first time and the fundamental possibility of exciting a thermonuclear reaction due to the chemical energy of explosives.

Yury Zamyatin took an active part in the preparatory work to justify the charge scheme and directly in the measurements at the testing ground. The RDS-6s thermonuclear charge was tested on 12 August, 1953. It was important to confirm that it was a thermonuclear reaction. Yu.S.Zamyatin and a group of colleagues proposed a technique based on the dependence of the distribution of fission fragments using mass on the energy of the neutrons causing fission. Together with radiochemists, the yields of the fragments were analyzed and it was established that the bulk of the fission occurred due to thermonuclear neutrons, that is, the explosion was thermonuclear. This conclusion meant that the USSR was the first in the world to construct a hydrogen bomb that could be transported by plane.

In the late 1950s, there was increased interest in transuranic elements, caused by a discussion about the possibility of using them in nuclear charges. With the direct participation of Yury Zamyatin, in 1958-1960, the fission cross-sections of isotopes of a number of heavy elements were measured: thorium-230, plutonium-240, plutonium-241, americium-241 with neutrons with an energy of 2.5 and 14 MeV.

Throughout his scientific career, Yury Zamyatin dedicated much effort to systematizing experimental data on the nuclear characteristics of heavy nucleus isotopes that played a major role in the Atomic Project. Already in 1959, a group of employees, with the scientific support of Zamyatnin, prepared and published a reference book on elementary nuclear constants. It was the first attempt to develop a nuclear data bank at VNIIEF and the systematization of data almost immediately bore fruit. Yury Zamyatin, using a simple approximation prototype, obtained data on the constants of some nuclei that had not yet been obtained experimentally.

From 1966 to 1976, he worked at NIIAR (Dimitrovgrad, until 1972 - Melekess), where he played a key role in the organization and development of nuclear research, especially in the field of accumulation of transuranic elements and neutron spectrometry, influencing both fundamental research and practical applications of nuclear physics. In 1972, under his supervision, a department was established focusing on neutron spectrometry and fundamental research in nuclear physics. Yury Zamyatin improved the techniques of neutron spectrometry, using the horizontal channels of the reactor for detailed investigations of neutron interactions. Under his supervision, experiments were carried out to study ternary fission, deepening the understanding of fission processes and the behavior of fission fragments.

Ivan Ruskov demonstrated slides of several publications by Yury Zamyatin in the journal "Atomic Energy" and the investigations of V.M.Maslov (JIPNR, Minsk) in 2023 that included the results obtained by Yu.S.Zamyatnin and his colleagues in 1960. He also spoke about the development of research facilities at VNIIEF and the ENGRIN FLNP project to study prompt neutron emission in nuclear fission.

The memory of Yury Zamyatin lives not only in the hearts of his colleagues that knew him, but also in published nuclear data and experimental facilities developed by Zamyatnin, his colleagues and students.

Olga TARANTINA