Izvestiâ Akademii nauk SSSR. Seriâ fizičeskaâ

The formation of high-excited states (Ex > 8 MeV) of neutron-rich isotopes of helium and lithium was studied in the absorption reactions of stopped pions by nuclei ⁹Be, ^10,11B and ^12,14C. For most nuclei, the results were obtained in several reaction channels at once. Candidates for cluster resonances and isobar-analog states have been observed.

Spectra of deuterons and tritons were measured at the absorption of stopped π — mesons on a “live” target (analog of the ²⁸Si target). It is shown that the application of this method makes it possible to identify “direct” mechanisms of the formation of deuterons and tritons. An estimate of the proportion of these particles in total yields was obtained, which was ~ 30 %.

A variant of testing threshold SiO₂ aerogel Cherenkov detectors using cosmic radiation is described. The implementation requires a minimum amount of additional electronics and does not involve massive absorber layers (e. g., lead). The method makes it possible to accurately determine efficiency of detectors under study and to study operation of detectors in different energy ranges for relativistic charged particles. Good agreement between the results of the simulation and measurements was obtained.

To study the cluster structure in the reactions of interaction of fast neutrons with ⁹Be, the kinematics of the reactions n + ⁹Be → α + ⁶He and n + ⁹Be → ⁸Be + 2n → 2 α + 2n at energies of 1—3 MeV were simulated. The possibility of determining the characteristics of reaction channels under the interaction of a neutron with a ⁹Be nucleus by measuring the ionization losses of charged reaction fragments in a multilayer gas-filled charged particle detector with a beryllium converter has been demonstrated.

An experiment to determine the low-energy parameters of np interaction in the nd breakup reaction at a neutron energy of 5 MeV of the RADEX channel of the INR RAS is proposed. The energy of the virtual ¹S₀ state and the np scattering length can be obtained from the experimental dependence of the reaction yield on the relative energy of motion of the “breakup” neutron and proton in the kinematic region, where the np interaction in the final state is most pronounced. The reaction events were simulated, based on which the optimal conditions for the future experiment were selected.

The modern vertex detectors based on silicon sensors: track systems of the leading experiments at the Large Hadron Collider, as well as vertex detectors of the MPD and SPD experiments at the NICA collider have been discussed. The development of concepts for new detector complexes using thin silicon pixel detectors for precision identification of decay vertices of charmed hadrons was considered. Also, the results of work on the development of cooling systems for large area ultrathin silicon detector modules and the results of studies of properties and characteristics of silicon pixel sensors based on CMOS technology was presented in the context of rare hadron (containing heavy quarks) decays detection.

We consider the studies of theoretical groups of A. Bulgac (Washington University, Seattle) and J. Randrup [Lawrence Berkeley National Laboratory (LBNL)], demonstrated various approaches of correlations of angles between the spins of fragments of double spontaneous and low-energy fission. The idea of the theoretical group of J. Randrup (Lawrence Berkeley National Laboratory (LBNL)) about two-dimensional (2D) and three-dimensional (3D) spin was analyzed, results for ²³²Th(n, f), ²⁵²Cf(sf), ²³⁸U(n, f) compared to A. Bulgacs (Washington University, Seattle) group. The special geometry of the dividing nucleus is considered.

The authors consider the problem of describing theoretically the dynamics of nucleon clustering inside a fissile nucleus. The approach is based on the microscopic modeling of clustering as a new type of collective particle motion. The use of a dynamic clustering algorithm in the region of heavy nuclei requires effective multiparticle interaction to be developed for a distributed microscopic model. Calculations are performed for a double magic cluster that plays an important role in the formation of the second minimum of the fission barrier observed in the multimodal fission of heavy nuclei.

Equations of quantum hydrodynamics were obtained from the Schrödinger equation considering dissipation, which in the semiclassical limit are reduced to the traditional equations of hydrodynamics of an ideal fluid. An analytical solution to the hydrodynamic equations is found in the quantum shock wave approximation in one-dimensional and two-dimensional cases. The dissipative function can be found in the nonequilibrium approach. A comparison is made with experimental data to describe the emission of protons in collisions of medium-sized atomic nuclei of intermediate energies.

There are summarized modernization results of the BR-K1M (booster-reactor cascade) research nuclear facility. There are discussed research results of the facility start-up second stage, measuring and processing techniques, used to obtain the main characteristics of reactor active zone, operational parameters, and limit values for safe facility operation.

Using formulae for calculating the widths of spontaneous and thermal neutron-induced ternary fission of atomic nuclei with the light charged particles emission, based on the approach to ternary fission as a virtual process, as well as experimental energy distributions of α-particles, hydrogen isotopes and ⁶He nuclei in ternary fission of actinide nuclei, the probabilities of the third particles formation in the neck of the fissile nucleus, which turn out to be close to each other for (s, f) and (n_th, f) fission reactions of the corresponding nuclei, were estimated. It was shown, that the spontaneous and induced ternary fission of the actinide nuclei under consideration with the emission of light charged particles and nucleons comes from close configurations of the fissile nucleus, and the thermal neutron binding energy introduced into the compound fissile nucleus in reactions (n_th, f) goes into the deformation energy of the fissile nucleus, and not into the kinetic energy of the third particle.

Using the Quartus software environment, simulation of time measurements for a fast collision monitor of particle beams based on chevron MCP assemblies was carried out. The measurement algorithm is based on the delayed coincidence method. 4-channel electronics for a detector on microchannel plates (MCP) based on high-speed comparators and FPGA EPM240 from ALTERA have been created. The test prototype was tested using a 4-channel nanosecond pulse generator, with an adjustable delay between channels. When using these comparators and FPGAs, it is possible to determine the time of registration of particles by a detector with an error of 100 ps, while the calculated speed of the reading circuit coincides with the measured one and is no more than 10 ns for each event for a 4-channel system.

Total cross sections s_{d, xt} of reaction ⁹Be(d, xt) were measured in the range of deuteron energies 1.5—12 МeV with error 8.3 % using activation reaction ⁹Be + t → a + ⁸Li + 2.927 МeV (T_1/2 = 0.84 s, E_bмах = 13 МeV) by B. Ya. Guzhovskii’s method on electrostatic tandem accelerator EGP-10 (RFNC—VNIIEF). In 1 mm thick beryllium layer primary target and convertor functions were combined which was possible provided that the layer thickness was more than a sum of primary deuterons and secondary tritons paths. Justification of the method is presented. The absence of reliable data of mean energy of tritons produced in the reaction under investigation was the main problem in the activation cross sections acquisition. Obtaining of this value by measured tritons energy spectra was demonstrated. Spectrometric differential cross sections were obtained at the first time as well as total reaction cross sections. There is a good agreement between activation and spectrometric total cross sections.