Y. Masuda

Longitudinal asymmetry in a neutron radiative capture reaction of 139La

Abstract An asymmetry in the cross section for the neutron-induced reaction of 139 La was examined by a simultaneous measurement of the capture γ-ray and the neutron transmission. Sizable asymmetry was observed only in the p-wave resonance at E n = 0.734 eV. No significant asymmetry was observed in the other reactions. The asymmetry in the p-wave resonance was roughly constant as a function of E n . The average asymmetries in the resonance were A 1, γ = (9.5±0.3)% and A L,n = (9.7±0.5)% in the γ-ray and the transmission measurements, respectively.

Measurement of the parity violating asymmetry Aγ in n→+p→d+γ

The weak pion-nucleon coupling constant H{sub {pi}}{sup 1} remains poorly determined, despite many years of effort. The recent measurement of the {sup 133}Cs anapole moment has been interpreted to give a value of H{sub {pi}}{sup 1} almost an order of magnitude larger than the limit established in the {sup 18}F parity doublet experiments. A measurement of the gamma ray directional asymmetry A{sub {gamma}} for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine H{sub {pi}}{sup 1} independent of nuclear structure effects. However, since the predicted asymmetry is small, A{sub {gamma}} {approximately} 5 x 10{sup {minus}8}, systematic effects must be reduced to < 5 x 10{sup {minus}9}. The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors.

A measurement of the absolute neutron beam polarization produced by an optically pumped 3He neutron spin filter

Abstract The capability of performing accurate absolute measurements of neutron beam polarization opens a number of exciting opportunities in fundamental neutron physics and in neutron scattering. At the LANSCE pulsed neutron source we have measured the neutron beam polarization with an absolute accuracy of 0.3% in the neutron energy range from 40 meV to 10 eV using an optically pumped polarized 3 He spin filter and a relative transmission measurement technique. 3 He was polarized using the Rb spin-exchange method. We describe the measurement technique, present our results, and discuss some of the systematic effects associated with the method.

Parity non-conserving effect in the neutron radiative capture reaction

Helicity dependence was observed for the resonance of the neutron radiative capture reaction of139La using a polarized neutron beam. The polarized neutron beam was produced by a dynamically polarized proton filter. The neutron polarization was about 70 % throughout the measurement. The preliminary result of the asymmetry in theγ-ray count was (9.5±1.2) %. Experiments were also carried out for98Mo,108Pd and129Xe. Such a large asymmetry as that found in139La was not observed in these nuclei.

Polarized3He system for T- and P-violation neutron experiments

We have constructed an apparatus to polarize the3He nuclear spin, which will be used as a neutron spin analyzer in T- and P-violation neutron experiments. We report on principles and the present status of the method for the polarization of3He and the determination of its value.

Longitudinal asymmetry and γ-ray angular distribution in neutron-radiative-capture reactions

Abstract The parity-nonconserving effect was investigated in low-energy (n, γ) reactions for several nuclei with mass numbers of ~100. The longitudinal asymmetry ( A L ) was measured in p-wave resonances for 139 La and 81 Br taking into account the possible angular dependence within the framework of the sp mixing model. A L for 139 La was found to be independent of the γ-ray energy thresholds within the experimental errors. From these results the relation between a γ-ray detection experiment and a neutron-transmission experiment is discussed. A L was measured in the p-wave resonances for 81 Br, 93 Nb, 108 Pd, 111 Cd, 124 Sn and 139 La. The obtained nonzero values of A L are A L = (9.8 ± 0.3)%, (2.1 ± 0.1)% and −(1.3 +0.7 −0.4 % for 139 La( E p = 0.734 eV), 81 Br( E p = 0.88 eV) and 111 Cd( E p = 4.53 eV), respectively. A theoretical interpretation is discussed in terms of the interference between two amplitudes of the s- and p-wave incident neutrons.

Observation of parity-violating neutron spin rotation in the n-139La p-wave resonance

Abstract Parity-violating spin rotation of neutrons in a 139La target was observed in the vicinity of the 0.734 eV p-wave resonance. The measured angle of rotation, φpnc(E), shows a large enhancement around the resonance. The data are fitted with a theoretical function from the s-p mixing models of the parity-violation enhancement, yielding a parity mixing matrix element xW = 1.04 ± 0.40 meV which is in agreement with those previously obtained from the longitudinal asymmetry in the p-wave resonance cross section.

T-violation neutron experiment and polarized3He

An experimental scheme of the spin detailed balance in polarized neutron transmission through a polarized nuclear target is discussed for the T-violation test. The value of the spin detailed balance is estimated by using the data of the scattering amplitudes. The nuclear polarizations of proton,3He and139La are discussed for the T-violation experiment.

Precision Measurement of Parity Violation in Polarized Cold Neutron Capture on the Proton: the NPDγ Experiment

The NPDγ experiment at the Los Alamos Neutron Science Center (LANSCE) is dedicated to measure with high precision the parity violating asymmetry in the γ emission after capture of spin polarized cold neutrons in para‐hydrogen. The measurement will determine unambiguously the weak pion‐nucleon‐nucleon (πNN) coupling constant fπ1.The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is dedicated to measure with high precision the parity violating asymmetry in the

He3 polarization via optical pumping in a birefringent cell

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