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One of the applications of neutron spectroscopy for applied purposes is a nondestructive determination of the isotopic composition of samples under study. The method is based on the registration of neutron resonances and the measurement of the yield of reaction products in the resonances. The resonance energies are known practically for all stable nuclei and the set of energies does not coincide completely for any pair of isotopes. It allows determining the isotope composition. These measurements have been performed for a number of targets at the IREN Facility.

The yield of delayed neutrons, vd, from thermal-neutron-induced fission of 245Cm is measured. Experiments aimed at studying the properties of delayed neutrons from the fission of some reactor isotopes and initiated in 1997 were continued at the upgraded Isomer-M facility by a method according to which a periodic irradiation of a sample with a pulsed neutron beam from the IBR-2 reactor was accompanied by recording emitted neutrons in the intervals between the pulses. The accuracy of the resulting total delayed-neutron yield vd = (0.64 ± 0.02)% is two times higher than that in previous measurements. This work was performed at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (JINR, Dubna).

The delayed-neutron yield from thermal-neutron-induced fission of the 237Np nucleus was measured using a sample periodically exposed to a pulsed neutron beam with subsequent detection of neutrons during the time intervals between pulses. The experiment was realized on an Isomer-M setup mounted in the IBR-2 pulsed reactor channel equipped with a mirror neutron guide. The setup and the experimental procedure are described, the background sources are thoroughly analyzed, and the experimental data are presented. The total delayed-neutron yield from 237Np fission induced by thermal neutrons is ν d = 0.0110 ± 0.0009. This study was performed at the Frank Laboratory of Neutron Physics (JINR, Dubna).

The effect of parity violation in the interaction of thermal neutrons with lead was discovered in a number of studies. According to the existing theory, this effect is explained by the mixing of compound states characterized by different parities (s-and p-wave resonances). In view of the absence of a p-wave resonance in the region of thermal neutron energies, it is of importance to reveal a level below the neutron binding energy, a so-called negative resonance. The energy dependence of the cross section for radiative neutron capture on lead was measured in the present study, and it is shown that, for the 207Pb isotope, the results of this measurement deviate from the \({1 \mathord{\left/ {\vphantom {1 {\sqrt E }}} \right. \kern-\nulldelimiterspace} {\sqrt E }}\) law, thereby suggesting the presence of a strong negative resonance. The parameters of this resonance are estimated.

The low-energy-gamma-ray spectra from neutron resonance capture with natural samples of Sb, Tb, Ho, and Ta were measured using the HPGe detector at the IBR-30 pulsed reactor at the JINR, Dubna. The resonance-spin-memory effect in the spectra from the odd-odd compound nuclei of 122Sb, 169Tb, and 166Ho was found to be quite distinct. For the 182Ta compound nucleus, it proved to be rather weak.

Three interference asymmetry effects in the angular distributions of fragments originating from 233U fission induced by resonance neutrons were measured. The energy dependences of the asymmetry factors being studied show sizable irregularities that are associated, according to modern theory, with the interference of s and p resonances at the stage of a compound nucleus. The basic features of weak p-wave resonances in the low-energy region were obtained from a global theoretical analysis of the asymmetry factors as functions of energy. The first estimates of nuclear matrix elements of weak interaction were derived for a few p-wave resonances.