L. N. Bondarenko

Neutron life time value measured by storing ultracold neutrons with detection of inelastically scattered neutrons

Abstract The neutron life time τ n was measured by storage of ultracold neutrons (UCN) in a material bottle covered with Fomblin oil. The inelastically scattered neutrons were detected by surrounding neutron counters monitoring the UCN losses due to upscattering at the bottle walls. Comparing traps with different surface to volume ratios the free neutron life time was deduced. Consistent results for different bottle temperatures yielded τ n sec =885.4±0.9 stat ±0.4 syst .

Analysis and correction of the measurement of the neutron lifetime

Corrections have been introduced into the result τβ = 885.4 ± 0.9stat ± 0.4syst s of our measurements of the neutron lifetime. The corrected value is τβ = 881.6 ± 0.8stat ± 1.9syst s.

Cooling and heating of ultracold neutrons during storage

The rare processes of weak heating and cooling of ultracold neutrons reflected from the surface of fluorosubstituted oil are studied. The probability of these processes is estimated at 10−6 per single reflection at energy transfer commensurate with the primary neutron energy. Weak heating and cooling are shown to be a manifestation of a more general phenomenon—quasielastic neutron reflection whose probability is dependent on temperature.

Angular correlation between the neutron spin and the antineutrino momentum in the neutron decay

Abstract The angular correlation between the neutron spin and antineutrino momentum in the beta decay of polarized neutrons has been measured accurately. The resulting coefficient B of the correlation is 0.995 ± 0.034.

A search for time-parity violation in the beta decay of polarized neutrons

Abstract The angular correlation between the directions of escape of an electron and neutrino and neutron spin in the beta decay of polarized neutrons is measured accurately. It is shown that time parity is not violated within the experimental error. The corresponding phase difference between the beta-decay constants gA and gV is θ = 178.7 ± 1.3 degrees.

Cold-neutron storage owing to diffusion reflection

Results are presented that were obtained from experiments devoted to storing very cold neutrons in vessels whose walls are made from structures involving a spatial inhomogeneity of the average Fermi potential. The possibility of storing neutrons owing to diffusion reflection from the walls is shown, and prospects of elaborating the method are discussed.

Flexible polyvinyl chloride neutron guides for transporting ultracold and very cold neutrons

The transmission of ultracold neutrons (UCNs) through flexible polyvinyl chloride (PVC) tubes with lengths of up to 3 m and an internal diameter of 6–8 mm has been studied. High UCN transmission is found even for arbitrarily bent tubes (single bend, double bend, triple bend, figure eight, etc.). The transmission can be improved significantly by coating the inner surface of the tube with a thin layer of liquid fluorine polymer. The prospects of these neutron guides in fundamental and applied research are discussed.

Storage of ultracold neutrons in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice

The possibility of attaining the calculated probabilities of the losses of ultracold neutrons (UCN) stored in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice is tested experimentally. It is found that UCN hitting the walls of a graphite vessel undergo additional inelastic scattering not predicted by the theory. It is shown that this scattering may be due to the presence of surface hydrogen that provides a channel of UCN leakage slightly varying with temperature. For vessels whose walls are coated with fluorine polymer oil, additional inelastic UCN scattering is also observed and is found to be efficiently suppressed with decreasing temperature. The experimentally observed and calculated values of the probabilities of UCN losses are shown to be in good agreement for vessels whose walls are made from heavy-water ice.

Measurement of cross sections for inelastic cold-neutron scattering in metals and polymers by the method of (n, γ) analysis

The results obtained by measuring the cross sections for the inelastic scattering of very cold neutrons for a number of metals and polymers by the method of a neutron-irradiation analysis are presented. The method is based on simultaneously measuring events of inelastic scattering and neutron capture in the sample under investigation via recording gamma radiation with a semiconductor germanium detector. Neutron capture by a nucleus of the sample is accompanied by the prompt radiation of gamma rays having a known spectrum. Upon inelastic scattering, a neutron acquires thermal energy. Upon leaving the sample, this neutron is absorbed in a special converter that contains the isotope 10B. The capture of the neutron by a 10B nucleus is followed by the emission of a 477-keV gamma ray. The probabilities of capture and inelastic scattering are proportional to the respective neutron-interaction cross sections, and the ratio of the recorded detector counts corresponding to events of the two types does not depend on the spectrum of the incident flux of very cold neutrons or on the trajectory of neutron motion in the sample. The sought inelastic-scattering cross section at a fixed sample temperature is calculated by using this ratio and the known cross section for neutron capture by the sample isotope having a known gamma-radiation spectrum.