The cross section for the neutron-induced fission of 237Np nuclei in the neutron energy range of 0.3–500 MeV has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute. The 237Np(n, f) fission cross section has been measured with respect to the 235U(n, f) fission cross section and fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The data obtained have been compared to the previous experimental results and to estimates from various evaluated data libraries.

The ^243 Am fission cross section was measured for incident neutron energies from 0.3 MeV to 500 MeV on the time-of-flight spectrometer of the neutron complex GNEIS at the NRC “Kurchatov Institute” – PNPI. Fission fragments were registered using position-sensitive low-pressure multiwire counters, which made it possible to simultaneously measure the angular distributions of fission fragments. As a result of processing these distributions, the energy dependence of the angular anisotropy of fission fragments of ^243 Am in a wide range of neutron energies was determined for the first time. The cross section of ^243 Am(n, f) was measured relative to the ^235 U(n, f) cross section. The obtained data are compared with the results of other experimental works. Theoretical estimates for the fission cross section and anisotropy of angular distribution of fission fragments for the ^243 Am(n, f) reaction are presented and discussed.

Analysis of the reliability of available experimental and evaluated data on cross sections for three (n, p) reactions leading to the formation of isotopes in isomeric metastable states is performed. This examination is motivated by recent measurements carried out with neutrons with energies of about 14 MeV at the NRC “Kurchatov Institute”. The possibility of using the TALYS-1.9 software package in order to evaluate cross sections of mentioned reactions is demonstrated.

The 236U fission cross section and the angular distributions of fragments from fission of 235U and 236U were measured for incident neutron energies from 0.3 to 500 MeV on the time-of-flight spectrometer of the neutron complex GNEIS at the NRC "Kurchatov Institute"-PNPI. Fission fragments were registered using position sensitive low-pressure multiwire counters. In the neutron energy range above 20 MeV, the angular distributions of 236U fission fragments were measured for the first time. The fission cross section of 236U(n, f ) was measured relative to the fission cross section of 235U(n, f ), which is an accepted international standard. The obtained data are compared with the results of other experimental works. Theoretical calculations of the fission cross section and the anisotropy of angular distribution of fission fragments for the 236U(n, f ) reaction performed within the framework of our approach are presented and discussed.

The cross section for the neutron-induced fission of 238U nuclei has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, in the neutron energy range of 0.3–500 MeV. Fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The cross section for 238U(n, f) fission has been measured with respect to the cross section for 235U(n, f) fission, which is an accepted international standard. Data on the energy dependence of the anisotropy of the angular distribution of fragments of neutron-induced 238U nuclei are also presented. The data obtained have been compared to previous experiments carried out using both similar and significantly different methods.

The $^{236}\mathrm{U}$ fission cross section and the angular distributions of fragments from fission of $^{235}\mathrm{U}$ and $^{236}\mathrm{U}$ were measured for incident neutron energies from 0.3 to 500 MeV on the time-of-flight spectrometer of the neutron complex GNEIS at the NRC ``Kurchatov Institute''--PNPI. Fission fragments were registered using position-sensitive low-pressure multiwire counters. In the neutron energy range above 20 MeV, the angular distributions of $^{236}\mathrm{U}$ fission fragments were measured for the first time. The fission cross section of $^{236}\mathrm{U}(n,f)$ was measured relative to the fission cross section of $^{235}\mathrm{U}(n,f)$, which is an accepted international standard. The obtained data are compared with the results of other experimental works. Theoretical calculations of the fission cross section and the anisotropy of angular distribution of fission fragments for the $^{236}\mathrm{U}(n,f)$ reaction performed within the framework of our approach are presented and discussed.

The cross section for the neutron-induced fission of 238U nuclei has been measured using the time-of-flight spectrometer of the GNEIS neutron complex at the Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, in the neutron energy range of 0.3–500 MeV. Fission fragments have been detected by low-pressure position-sensitive multiwire proportional counters. The cross section for 238U(n, f) fission has been measured with respect to the cross section for 235U(n, f) fission, which is an accepted international standard. Data on the energy dependence of the anisotropy of the angular distribution of fragments of neutron-induced 238U nuclei are also presented. The data obtained have been compared to previous experiments carried out using both similar and significantly different methods.

The quantum-mechanical solution to the problem of radiative recombination of an electron in a Coulomb field, obtained in the approximation of the smallness of the electron coupling with the radiation field, has been known for a long time. However, in astrophysics, the classical approach, which does not explicitly use this smallness, is sometimes used to describe similar processes in systems of magnetic monopoles or self-interacting dark matter particles. The importance of such problems is determined by the fact that recombination processes play a crucial role in the evolution of the large-scale structure of the Universe. Therefore, of particular interest is the fact that the classical and quantum expressions for the recombination cross section differ significantly in magnitude. It is shown that the applicability of quantum and classical approaches to radiative recombination is closely related to the radiated angular momentum and its quantization. For situations where the classical approach is not suitable, a semi-classical approach based on the angular momentum quantization is proposed, in some respects an alternative to the well-known semi-classical Kramers' approach.

In recent years, investigations of angular distributions of fragments in neutron-induced nuclear fission have been extended to intermediate energies, up to 200 MeV, as well as to a wide range of target isotopes. Using as an example the latest data obtained by our group for the reaction 237-Np(n,f), we discuss the specific features of fission fragment angular distribution and present a method for their simulation based on the code TALYS. It is shown that a simplified model reasonably describes energy dependence of the angular distribution in the whole range 1-200 MeV. The ways to improve the model are discussed along with the possibilities to use it for obtaining new information on fission and pre-equilibrium processes in neutron-nucleus interaction. We consider also the relevant problems of describing fission fragment angular distributions.

This work summarizes some results of a series of experiments aimed at the investigation of energy dependence of anisotropy of fission fragments (FFs) in (n, f) reactions for neutron energies from low to intermediate. Angular distributions of FFs from the neutron-induced fission of 239Pu, 237Np, and natPb have been measured in the energy range 1–200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the Petersburg Nuclear Physics Institute (Gatchina, Russia). The anisotropies of FFs deduced from the measured angular distributions are presented. In the neutron energy range above 20 MeV the results have been obtained for the first time in our works. The experimental data for FF anisotropy in 237Np(n, f) are compared with calculations based on "adapted" TALYS software.

Problems of describing experimental data on the angular distributions of fragments of nuclear fission induced by intermediate-energy neutrons are discussed. A way of calculating angular distributions based on using the TALYS program is proposed. The capabilities of the technique for obtaining new information on the fission process and reactions at intermediate energies are shown by the example of describing data obtained for the $${}^{{237}}{\text{Np}}$$ nucleus.

The measured angular distributions of fission fragments of 240Pu nuclei have been presented and theoretically analyzed. Measurements at energies above 10 MeV have been performed for the first time. A model description of the energy dependence of the angular anisotropy of fission fragments in the entire studied range of neutron energies has been proposed.

Angular distributions of fission fragments from the neutron-induced fission of Th, U, U, U, Pu, Np, Pb and Bi have been measured in the energy range 1‒200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron SC-1000 of the NRC KI PNPI (Gatchina, Russia). The data in the neutron energy range above 20 MeV for U, Pu, Np, Pb and Bi have been obtained for the first time. Recently, the list of nuclei to be studied within the framework of present investigation was filled with isotope Np. Neptunium is a major component of spent nuclear fuel, therefore an accurate knowledge of the fission cross-section and fragment properties is needed for waste transmutation and advanced nuclear facilities (reactors, ADS, etc.) studies. A description of the experimental equipment and measurement procedure is given. The underlying ideas of the theoretical approach developed for analysis of the obtained experimental data are discussed.