Vol 86, No 5 (2023)

The reliability of data on (Y, 1n) and (y, 2n) reactions on 59Co from several experiments carried out using beams of bremsstrahlung was investigated using the experimental-theoretical method of evaluation of photoneutron partial reaction cross sections based on objective physical criteria. It was found out that partial reaction cross sections obtained using the corrections to the neutron yield cross section σ(y, xn) = σ(y, 1n) + σ(y, 2n) calculated via statistical theory do not satisfy physical criteria of reliability. In experiments under discussion the (y, 1n) reaction cross sections were significantly unreliably underestimated, but the (y, 2n) reaction cross sections were, vice versa, overestimated. Evidently, this is because of some shortcomings of the method used for obtaining the information on partial reaction cross sections with the aid of corrections calculated via statistical theory.

The influence of exclusive prefission neutron spectra, (n, xnf)1,…x
, on the observed spectra of prompt fission neutrons (PFN), the total kinetic energy (TKE) of fission fragments (products), and the average number of prompt fission neutrons is studied. The (n, xnf)1,…x  exclusive neutron spectra correspond to a self-consistent description of the fission reactions (neutron emission) 
235U(n, F)(235U(n, xn))) and 239Pu(n, F)(239Pu(n, xn))) for neutrons of energy extending up to 20 MeV. An extensive experimental database of PFN spectra made it possible to study in detail (confirm) an intricate dependence of the shape of observed PFN spectra on the fissility of 236U  and 240Pu compound nuclei. This effect is found to be correlated with the contributions of (n, xnf)) emissive fission reactions and with the competition of (n,nγ) and  (n, xn)  reactions. The exclusive prefission neutron spectra of (n, xnf)1,…x  reactions and the exclusive neutron spectra of (n, nγ) and (n, xn)1,…x reactions were calculated by means of the Hauser–Feshbach formalism simultaneously with the (n, F)- and  (n, хn)- cross sections. It is shown that the angular anisotropy of exclusive neutron spectra of (n, xnf) reactions has a substantial effect on the observed spectra of prompt fission neutrons and their average energies . The ratio of the average PFN energies
 for the forward and backward emission of prefission neutrons in the reactions235U(n, xnf) and 239Pu(n, xnf)  agrees with experimental data. Partial components associated with(n, f) and (n, xnf). reactions are singled out in the observed PFN spectra. The input values of model parameters are fixed in describing PFN spectra of thermal-neutron-induced fission reactions. The potential of the approach being considered for predictions of PFN spectra and their average energies in the reactions 238U(n, F) and 240Pu(n, F)  is demonstrated.

The results of calculations of nucleosynthesis of heavy elements during the explosion of a low-mass neutron star are presented. The low-mass neutron star is formed as a result of the exchange of matter in the last stages of the evolution of a close binary system of neutron stars with a large initial mass asymmetry. Two variants of the scenario, which use different approximations of the equation of state of neutron star matter: BSk22 and BSk25, are considered. Their usage lead to different expansion dynamics of the shells of a low-mass neutron star. It is shown that the character of shock wave propagation and the abundance of heavy elements formed in the inner layers of the outer crust with 0.29 < Ye < 0.45, for these two scenarios are different, although the composition of the outer crust before the explosion differs insignificantly. These differences in the scenarios result in a noticeable difference in the calculated abundances of heavy elements both in these layers and in the entire examined part of the outer crust.

An ionization loss simulation in several sequent gaps of the neutron detector is performed. It is based on the boron-10 rigid layer converter and gaseous chamber. It was shown that the distribution of ionization losses over gas gaps varies significantly depending on the incident neutron energy. The fact can be used to control the energy of the neutron flux using this detector.