In collaboration with colleagues from Japan During April and May 2025, MLIT Deputy Director Ochbadrakh Chuluunbaatar performed joint work with colleagues from the Institute of the Institute of Multidisciplinary Research for Advanced Materials (IMRAM) of Tohoku University in Sendai, Japan. Ochbadrakh Chuluunbaatar arrived at IMRAM at the invitation of Professor Takahashi Masahiko. In 2024, experiments to investigate the elastic and inelastic scattering of electrons by atoms (including the helium atom) into the back hemisphere were conducted at this institute. Electron energy absorption spectra measured at a scattering angle of 135° and an incident electron energy of 2 keV demonstrated that with a large transfer of energy and momentum, which occur under such kinematic conditions of the experiment, the nucleus moved, resulting in a significant change in the course of the differential cross-section curve as an electron scattering angle function. Calculations in the first Born approximation showed that the differential cross sections of inelastic scattering 11S-21S and 11S-21P, as well as of elastic scattering 11S-11S (only singlet states are considered), were several orders of magnitude smaller than the experimental results. Therefore, calculations in the second Born approximation were performed, and it turned out that such a two-step mechanism played a decisive role for an adequate description of the reactions under consideration. In the second Born approximation, elastic and inelastic electron scattering cross sections are expressed through nine-fold singular integrals. During his short time at this institute, Ochbadrakh Chuluunbaatar reduced the integrals to regular single and double integrals using various integral transformations, which enabled to calculate with high accuracy elastic and inelastic scattering cross sections that completely coincided with the experimental ones. All computations were conducted on the JINR “Govorun” supercomputer. The theoretical part of the work was described by BLTP Senior Researcher Yuri Popov. At present, part of the results has been submitted for publication to the Physical Review A scientific journal.
