In the experiment "Neutrino-4" on the search for a sterile neutrino, the effect of oscillations was found at a confidence level of 3 standard deviations. In order to significantly increase the accuracy of the experiment, a second neutrino laboratory is created at the SM-3 reactor (Dimitrovgrad, Russia) and a new neutrino detector is developed. The scintillation-type detector consists of 4 modules having a multi-sectional structure with a horizontal arrangement of 100 sections with PMTs located on both sides of the section. The possibility of increasing the accuracy of the experiment by a factor of 2.7 is shown, which will make it possible to achieve a confidence level of more than 5 standard deviations and answer the question of the existence of a sterile neutrino.

The new physical effects of T-odd asymmetry of the emission of light charged particles (LCPs) during the ternary fission of some heavy nuclei by cold polarized neutrons have been experimentally studied. The coefficients of triple scalar and vector correlation of the pulses of light particles and fission fragments (TRI effect) and the fivefold correlation of the same vectors (ROT effect) have been measured. These effects are believed to be caused by the rotation of polarized fissioning system around its polarization direction. The treatment of the experimental data for LCPs in the framework of this hypothesis leads to a good agreement between the calculation results and experimental data. The calculated value of the angle of rotation of the fission axis in the ternary fission of the polarized fissioning 236U* compound nucleus was used to process the results of measuring the ROT effect for γ photons from binary-fission fragments of the same nucleus. A satisfactory description of these experimental data is obtained which serves a convincing confirmation of the rotation hypothesis.

The main results of studying the properties of “instantaneous” neutrons and γ photons during the fission of 233, 235 U( n th , f ) and 239 Pu( n th , f ) nuclei and spontaneous fission of 252 Cf, which were performed on the WWR-M reactor at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences, are presented. Along with obtaining the main characteristics of the instantaneous radiation from fission fragments, these studies were also aimed at gaining deeper insight into such exotic processes as the emission of break neutrons and γ photons from a fissioning nucleus near the break point. These investigations were performed on different experimental setups using different analytical methods. This approach allowed us not only to find but also to reduce to minimum possible systematic effects. The yields of break neutrons were found to be about (5–7) × 10 −2 of the total number of neutrons per 233, 235 U( n, f ) fission event and approximately twice as much for 239 Pu( n, f ) and 252 Cf. The coefficient of T -odd asymmetry for γ photons is in agreement with the estimate obtained on the assumption that the observed effect is mainly related to the γ photons emitted by excited fragments with highly oriented angular momenta. This fact gave grounds to conclude that the desired break γ photons cannot be reliably selected (within the obtained experimental accuracy) against the much larger background of γ photons from fission fragments.

Prospects for further studies of TRI and ROT effects of T-odd asymmetry in the emission of light particles in the ternary and binary fission of heavy nuclei that is induced by slow polarized neutrons are considered with a view to studying the mechanism for the formation of these effects and using them to get new information about fission dynamics. It is planned to investigate the dependence of the corresponding T-odd-asymmetry coefficients on the main characteristics of the fission reaction.

Conditions for formation of angular and energy distributions of light particles emitted in ternary fission of 233, 235U, 239Pu, and 245Cm nuclei induced by cold polarized neutrons have been studied in the course of investigating T-odd asymmetry in emission of these particles with respect to the plane formed by the fission axis and the polarization axis of the fissioning nucleus. The results obtained lead to the conclusion that in ternary fission charged particles are emitted by the fissioning nuclear system rotating around the polarization direction.

A new approach for describing fission is briefly presented. It is similar to the convenient theory of nuclear reactions, involves the helicity representation for exit fission channels, and combines the multimode fission representation with the A. Bohr's concept of transition states. This approach provides formulas for partial and differential fission cross sections. The formulas are applied to analyze the angular anisotropy of fragments from the fission of aligned U-235 nuclei induced by resonant neutrons. The P-even forward-backward and right-left angular correlations or P-odd correlations caused by the interference of s- and p-wave neutron resonances are also analyzed.