N. A. Gundorin

Observation of neutron standing waves at total reflection of polarized neutrons by precision gamma-spectroscopy

Abstract Total reflection of polarized neutrons from the layered structure glass/Fe/Gd was investigated by registering both the reflected neutrons and gamma-quanta from thermal neutron capture. The ratio of gamma counts measured at two polarization states of neutrons proves that over the surface of the Fe layer a neutron standing wave is formed.

Isotope-Identifying neutron reflectometry

The possibilities of an isotope-indentifying study of layered structures in different regimes of a neutron wave field are considered. The detection of specularly reflected neutrons and secondary radiation (caused by neutron capture) in the form of charged particles, γ quanta, and nuclear fission fragments, as well as neutrons spin-flipped in a noncollinear magnetic field and on nuclei of elements with spin, makes it possible to implement isotope-indentifying neutron reflectometry.

Nature of parity violation in neutron interaction with lead

AbstractThe 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

Measurement of delayed-neutron yield from 237Np fission induced by thermal neutrons

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A Hemispherical Fission Chamber for the Neutron-Flux Monitoring

law, thereby suggesting the presence of a strong negative resonance. The parameters of this resonance are estimated.

Measurements of the partial cross section for the reaction 48Ti(n, γ1)49Ti and estimation of the radiative strength functions for E1 and M1 transitions

The partial cross section for radiative neutron capture accompanied by gamma transitions to the ground state of the 59Ni nucleus was measured as a function of energy by a new neutron-spectrometry method that employed the shift of a primary gamma transition in response to a change in the energy of the captured neutron. The reaction 7Li(p, n)7Be was used as source of neutrons for the present measurements. The protons that induced this reaction were accelerated by a Van de Graaff electrostatic generator to energies exceeding the reaction threshold by 60 keV, in which case an appropriate geometry of the experiment permitted irradiation of the sample under study with neutrons whose energy ranged between 10 and 120 keV. The partial widths of some resonances and radiative strength function for hard primary M1 gamma transitions were determined in addition to the above cross sections.

Resonance-spin memory in low-energy-gamma-ray spectra from Sb, Tb, Ho, and Ta odd-odd compound nuclei

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 νd = 0.0110 ± 0.0009. This study was performed at the Frank Laboratory of Neutron Physics (JINR, Dubna).

keV – Neutron Spectrometry Method for Partial Cross Section Measurements

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).