[en] A proof-of-principle experiment using unpolarized low-energy neutron capture on polyethylene and an array of 12 CsI detectors operated in current mode has been performed to test the possibility of measuring at LANSCE the parity-violating asymmetry A_γ in the angular distribution of 2.23 MeV gamma rays from the n→+p→d+γ reaction. Results of this experiment including the current mode signal, electronic noise and detector sensitivity to magnetic fields are reported. The motivation and conceptual design for a new experiment aimed at a 10-fold improvement in the accuracy of A_γ are outlined

[en] The use of nuclear-spin polarized ³He as a spin filter for low energy neutron beams is discussed and many properties of these polarizers are described. We compare this technique to other methods for polarizing neutrons of energy 0.01-100 eV. The status of a joint IUCF/NIST project for constructing transmission polarizers using both Rb spin-exchange and metastability-exchange optical pumping is presented. (orig.)

[en] 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 ³He spin filter and a relative transmission measurement technique. ³He 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

[en] High accuracy, absolute measurements of the neutron total cross section for ³He are reported for incident neutron energies 0.1-400 eV. The measurements were performed at the LANSCE short-pulse neutron spallation source. Using the previously determined cross section for neutron elastic scattering, 3.367±0.019 b, we extract a new value for the energy dependence of the ³He(n,p)³He reaction cross section, σ_np=(849.77±0.14±1.02)E^-1/2-(1.253±0.00±_-0.049^+0.008)b, where the neutron energy is expressed in eV. The first uncertainty is statistical, the second systematic.

[en] Dense samples (10-100 bar cm) of nuclear spin polarized ³He are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high ³He polarizations (≅80%) at low pressures (few mbar). We describe a polarized ³He gas compressor system which accepts 0.26 bar l h^-1 of ³He gas polarized to 70% by a 4 W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5 bar cm target with final polarization of 55%. The spin relaxation rates of the system's components have been measured using nuclear magnetic resonance and a model of the ³He polarization loss based on the measured relaxation rates and the gas flow is in agreement with a ³He polarization measurement using neutron transmission

[en] The weak interaction between neutrons and protons has never been resolved experimentally. In analogy with the strong NN interaction, the weak NN interaction at low energy can be parametrized in terms of a meson exchange model with parity violating meson-nucleon couplings. Unlike the measured proton-proton weak interaction, the neutron-proton weak interaction is sensitive to the weak pion-nucleon coupling constant H_π¹. This coupling, which is responsible for the longest-ranged part of the weak NN interaction and is therefore an essential part of any description of weak interactions in nuclei, remains undetermined despite many years of effort. A measurement of the gamma ray directional asymmetry A_γ in the capture of polarized neutrons by parahydrogen has been proposed at Los Alamos National Laboratory. The goal of this experiment is to determine A_γ with a relative standard uncertainty of <5x10^-9, which is smaller than all modern predictions for the size of the asymmetry. The design of the experiment is presented, with an emphasis on the techniques used for controlling systematic errors

[en] A large area polarized ³He neutron spin filter has been developed and tested in long-term operation. The polarizer cells have area 50cm² and larger allowing access to a large area neutron beam. Polarization of ³He up to 57+/-1% was measured by monitoring the neutron transmission through the ³He. The polarization was maintained over the course of several weeks, but the maximum attainable polarization declined over the course of a year-long run as the cell degraded, possibly due to long-term exposure to the neutron beam at high temperatures. The resulting neutron polarization and transmission are velocity dependent and are optimized for 5A. Cell construction, polarizer design, performance, and polarimetry are described in this paper