On 13 July 2019, a prominent theoretical physicist Academician Semyon Solomonovich Gershtein who greatly contributed to nuclear physics, particle physics and astrophysics turned 90.

Semyon Solomonovich was born in Harbin (Manchuria) in a family of Soviet citizens. In 1936, he moved to Moscow with the family. In 1937 – 1938, his parents were repressed (in 1955 – 1956 were fully discharged). Since he was 8 years old, he was brought up by his grandmother A. I. Mendelevich.

In 1946, Semyon Solomonovich graduated from the secondary school and was admitted to the MSU Physics Department. In 1951, he graduated from the university and was sent for work at the secondary school of the Belousovo village (Kaluga region) where he spent three years. In spite of a large amount of work at school, S. S. Gershtein passed exams on theoretical minimum assessed by L. D. Landau and was the last one to be examined personally by Landau. After the exam on theoretical minimum, L. D. Landau recommended Gershtein to Ya. B. Zeldovich jointly with whom Gershtein made his first publication.

Another joint result of S. S. Gershtein and Ya. B. Zeldovich that became widely famous was the discovery of the top limit for the sum of masses of stable neutrino made in 1966. This limit increased for several times the limits for masses of muon and later discovered τ-neutrino obtained in laboratory experiments. The opportunity to make such estimations stimulated the merge of cosmology and particle physics.

In spring 1955, when P. L. Kapitsa took the post of Director of the Institute of Physical Problems again, L. D. Landau managed to invite S. S. Gershtein for making a postgraduate degree. After the defence of the candidate’s dissertation in 1958, Semyon Solomonovich worked in the Leningrad Physical and Technical Institute for two years where he met his friends V. N. Gribov, Yu. V. Petrov and other colleagues. In the early 1960s, he moved to Dubna for work in the Laboratory of Theoretical Physics JINR on the invitation of A. A. Logunov and N. N. Bogoliubov. This move was mostly connected with the fact that several experiments on the fields of his research were being prepared in the Laboratory of Nuclear Problems. Continuing work started by A. D. Sakharov and Ya. B. Zeldovich, S. S. Gershtein developed a theory about mesomolecular processes and nuclear reactions of synthesis of isotopes of hydrogen caused by muons. Experimental research conducted in Dubna, PNPI, and other meson factories abroad confirmed his predictions. Several international conferences on mu-catalysis were held, and the “Muon Catalyzed Fusion” journal was issued.

One of the most fascinating mesoatomic processes considered by S. S. Gershtein was the fast transitions between levels of hyperfine structures of mesoatoms happening thanks to muon exchange after interaction of the mesoatom with the nucleus of the same isotope of hydrogen. The same strong influence of transitions of mesoatoms into the lower state of hyperfine structure on the possibility of µ- catalysis was discovered (Gershtein-Wolfenstein effect). Mesomolecular processes and the μ-capture became the objects of the doctoral dissertation of S. S. Gershtein opponents of which were Academicians A. D. Sakharov, B. M. Pontecorvom and A. M. Baldin.

In 1962, before neutral currents were discovered and neutrino experiments were conducted, Semyon Solomonovich jointly with R. A. Eramzhian and Nguyễn Văn Hiệu showed that it is possible to use the nuclei excitation in neutrino scattering to search for currents in the fields of average energies. This process became then the most incontrovertible proof of oscillations of solar neutrino and validity of the Standard Model of the Sun.

In 1964, S. S. Gershtein started his work in the Institute of High Energy Physics and took an active part in the development of the research programme for the constructed accelerator. Jointly with a team of experimentalists, he participated in the drafting of the programme of neutrino experiments, including experiments with photoemulsions, to search for short-living particles. On his initiative and according to his estimations, an intensive electron beam with the energy of 46 GeV was produced at the proton accelerator for the first time ever. It was impossible to achieve such energy at electron accelerators of those times, and S. S. Gershtein took part in experiments on photoscattering conducted jointly by the Lebedev Physical Institute, the Yerevan Physics Institute, and IHEP.

Later on, Semyon Solomonovich together with his students conducted a set of experiments on the production of charm quarks in neutrino experiments.

After the b-quark discovery, S. S. Gershtein with his students made a set of research in which they measured the mass spectrum, the length of life and the meson production cross-section consisting of a b-quark and a c-antiquark and its excitations that was later confirmed in experiments at FLNAL and LHC colliders. The latest measurements (2019) made by the CMS, LHCb and ATLAS teams at the LHC collider found out radial excitations of the meson mentioned earlier. The study of the hadron production consisting of heavy quarks allowed scientists to estimate characteristics of another object, a baryon with two heavy quarks. Predictions of the theory were confirmed in 2018 when the baryon with two charm quarks was observed for the first time.

Jointly with V. S. Imshennik and other colleagues, S. S. Gershtein studied the role of neutrino radiation in the thermonuclear explosion of supernovas of the SN1А type. He suggested an original mechanism of collective acceleration of solar cosmic rays and expressed an idea that gamma-ray bursts are connected with specific flashes of massive stars.

In recent years, Semyon Solomonovich considered some consequences of the field gravitation theory developed by A. A. Logunov.

S. S. Gershtein has been teaching physics for many years. In 1958 – 1959, he was a professor in the Leningrad Polytechnic Institute. In 1961 – 1962, he taught students in the Dubna branch of the MSU Physical Faculty. Since 1963, he has been delivering general courses on theoretical physics in MIPT. Among their students, there are prominent scientists who recall him with gratitude. Semyon Solomonovich is proud by merit that four his students from the Belousovo school became Doctors of Sciences, and more than ten of his students worked in the Institute of Physics and Power Engineering in Obninsk after the graduation from MEPhI. He has always actively supported young talented scientists and talented people at large. He established and was engaged in numerous new scientific branches of not only theoretical but also experimental physics.

S. S. Gershtein spent lots of time popularizing science. Being a member of the editorial staff of the encyclopedia “Physics of microworld” and an assistant editor of the Great Soviet Encyclopedia, he wrote more than a dozen articles for these issues. Nowadays, he is a member of the editorial staff of journals “Priroda” (lit. “Nature”), “Yadernaya physica” (lit. “Nuclear physics”), and “TMP”. He is a member of the RAS Division Office of Physical Sciences.

S. S. Gershtein is distinguished by his friendliness but an uncompromising attitude to various displays of malpractice in science and human relations. He has always denied the clannish approach to solving controversial issues, and he has never got tired to repeat that “the compelling stand is the only right one.”

Colleagues, students, and friends cordially congratulate Semyon Solomonovich on his jubilee and wish him good health and new creative achievements.

A. F. Andreev, S. P. Denisov, A. M. Zaitsev, S. V. Ivanov, A. K. Likhoded, V. A. Matveev, V. A. Petrov, V. A. Rubakov, A. N. Skrinsky, N. E. Tuirin