V. A. Vesna

Investigation of P-odd correlations in the capture of thermal polarized neutrons involving emission of secondary charged particles (technical issues)

Abstract An installation for measuring parity violation in reactions with polarized neutrons involving the emission of secondary charged particles is described. The main part of the experimental setup is a multisection proportional chamber operated in the current mode. The 6Li(n,α)3H and 10B(n,α)7Li reactions are studied. The P-odd asymmetry was measured with an accuracy of δ ∼ 5 × 10−8.

Discovery of a P-odd effect in triton emission from the reaction 6Li(n, α)3H

The results of measuring the P-odd asymmetry (Sn · Pt) for triton emission from the reaction 6Li(n, α)3H are presented. Here, Sn is the neutron spin and Pt is the triton momentum. Three series of measurements were performed, one at the Petersburg Nuclear Physics Institute (Gatchina, Russia) in a vertical neutron beam from the PWR reactor and two in the PF1B beam from the reactor at the Institute Laue-Langevin (Grenoble, France). On the basis of all three experiments, the P-odd asymmetry coefficient was found to be αPN = −(8.6 ± 2.0) × 10−8. The results of zero experiments and calculations give every reason to believe that the above P-odd asymmetry is due to the reaction being studied.

A search for P-odd and P-even correlations in the 35Cl(n,p)35S reaction

The experiment of the forward-backward asymmetry α FB in the 35 Cl(n,p) 35 S reaction has been carried out with resonance neutrons up to 1 keV. Starting from the theoretical background the cross section and the asymmetry coefficients have been calculated and analyzed together with the experimental values of the p-odd (α PN ) and left-right (α LR ) asymmetry observed in the capture reaction of polarized thermal neutrons.

New version of the integrated method for measuring small effects in experiments on beams extracted from a nuclear reactor at the effect sign switching frequency above the fundamental frequencies of the reactor power fluctuation spectrum

The principles of construction and the results of testing of a system for measuring P-odd asymmetries in nuclear reactions with polarized cold neutrons by the integrated method of recording events at the neutron polarization switching frequency above the fundamental frequencies of the reactor power fluctuation spectrum are presented. It is shown experimentally that if the signal under investigation is characterized by the spectral density of power decreasing with increasing frequency, switching of the equipment at a higher frequency decreases the measuring error. The dependence of the error of measurements of P-odd asymmetry in the emission of γ quanta in the 10B(n, α)7Li* ⟹ γ ⟹ 7Li(g.s.) reaction on the neutron polarization switching frequency is derived. The system described here is implemented experimentally for the first time.

Search for P -ODD Asymmetry in the Radiative Cross-Section of the Interaction of Neutrons with Lead Nuclei ¶

The P-odd effect in the radiation cross section of capture of longitudinally polarized neutrons in a sample of natural lead is measured. The experiment was performed at PF1B facility at the Institut Max von Laue-Paul Langevin. The neutron polarization Pn was 92%, the total flux of polarized neutrons was ∼3 × 1010 n/s, and the mean neutron wavelength was λ = 4.7 Å. Taking into account “0-test” we estimated the asymmetry: aγ(natPb) = (2.3 ± 3.5) × 10−7, i.e., αγ ≤ 8.1 × 10−7 at 90% confidence level.

A method to measure neutron polarization using P-even asymmetry of γ-quantum emission in the neutron-nuclear interaction

A new method to measure polarization of cold/thermal neutrons using P-even asymmetry in nuclear reactions induced by polarized neutrons is proposed. A scheme profiting from a large correlation of the neutron spin and the circular γ-quantum polarization in the reaction (n, γ) of polarized neutrons with nuclei is analyzed. This method could be used, for instance, to measure the neutron-beam polarization in experiments with frequently varying configuration. We show that high accuracy and reliability of measurements could be expected.

Recent results of measurements of the 14N(n,p)14C, 35Cl(n,p)35S, 36Cl(n,p)36S, and 36Cl(n,α)33P reaction cross sections

Experiments are reported for measuring the cross section of the 14N(n,p)14C reaction over the neutron energy range from thermal energy to 150 keV at the IBR‐30 pulsed booster at JNR, Dubna and the WWR‐M reactor at INR, Kiev. The reaction cross section values were found for the thermal energy and for the neutron energies of 24 keV, 54 keV, 144 keV. The 36Cl(n,p)36S cross section was measured for the neutron energies from thermal energy to approximately 800 keV at the neutron source of LANSCE, Los Alamos. The contributions of the 36Cl(n,p)36S and 36Cl(n,α)33P reactions to resonances at 0.9 keV and 1.3 keV were identified. Also, at the WWR‐M reactor of PINR, Gatchina, preliminary measurements of the 36Cl(n,p)36S cross section at the thermal neutron energy were conducted. The 35Cl(n,p)35S reaction cross section was measured at the IBR‐30 pulsed booster.