[en] Neutron inelastic scattering from thulium-169 has been studied for states above 100 keV via the (n,n'γ) reaction at incident energies in the 0.2- to 1.0-MeV range. A high-resolution Ge spectrometer in conjunction with the time-of-flight technique was utilized. Thirty-six gamma-ray transitions from 16 levels were observed. Gamma-ray angular distributions were measured at E_n=750 keV and excitation functions at 125 degrees were measured in 50 keV steps over the range of incident energies. Differential gamma-ray production cross sections and gamma-ray branching ratios were obtained. Inferred neutron inelastic level cross sections of the four lowest ground-state rotational band (K^π=1/2⁺) members are compared to the sum of calculated compound nucleus and direct interaction cross sections. For the remaining levels, measurements are compared to compound nucleus calculations only. The comparison shows generally good agreement particularly near threshold

[en] We have measured the brightness of the Flight Path 12 upstream/back-scattering partially coupled cold hydrogen moderator at LANSCE. This measurement was performed in the neutron energy range of 0.8-76.9 meV by using a time-of-flight technique in conjunction with a two-pinhole collimator system. Cold neutrons were observed with a redundant ⁶Li-loaded glass scintillation detector having an efficiency of close to unity. The detector viewed an area of 0.93 cm² on the center of the 12x12 cm² moderator surface. A maximum brightness of 1.25x10⁸ neutrons s^-1 sr^-1 cm^-2 meV^-1 μA^-1 was measured at 3.3-meV neutron energy. Statistical and systematic errors of the measurement are 3% and 7%, respectively. The measured brightness is compared to the result of a model calculation and there is a significant disagreement, by a factor of 1.5 at the peak. The performance of the m=3 supermirror neutron guide system on Flight Path 12 was also studied with the two pinhole-detector system

[en] Neutron inelastic scattering from thulium-169 has been studied for states above 100 keV via the $\text{(n,n′γ)}$ reaction at incident energies in the 0.2- to 1.0-MeV range. A high-resolution Ge spectrometer in conjunction with the time-of-flight technique was utilized. Thirty-six gamma-ray transitions from 16 levels were observed. Gamma-ray angular distributions were measured at $\text{E}{}_{\mathrm{n}}\text{=750}$ keV and excitation functions at 125 degrees were measured in 50 keV steps over the range of incident energies. Differential gamma-ray production cross sections and gamma-ray branching ratios were obtained. Inferred neutron inelastic level cross sections of the four lowest ground-state rotational band $\text{(K}{}^{\mathrm{\pi }}\text{=1/2}{}^{\mathrm{+}}\text{)}$ members are compared to the sum of calculated compound nucleus and direct interaction cross sections. For the remaining levels, measurements are compared to compound nucleus calculations only. The comparison shows generally good agreement particularly near threshold.

[en] The absolute differential cross sections for the ³He(γ,n)pp reaction were measured as a function of outgoing neutron scattering angle and energy at the incident γ-ray energies of 12.8, 13.5, and 14.7 MeV to within a precision better than ±6%. Both the absolute cross sections and the neutron energy distributions at each incident γ-ray energy agree with the state-of-the-art theoretical results when the Coulomb interaction in the final state is included.

[en] We describe the design, construction, and performance of a set of saddle coils used to maintain the spin of a polarized proton target in the transverse direction with respect to the incident gamma-ray beam direction. The transverse coil assembly consists of two racetrack shaped coils formed from a single strand of thin NbTi superconducting wire. Four layers of NbTi per saddle coil were wet wound in a racetrack shape and then installed on a cylindrical support tube and epoxyed to prevent them from moving when the coils were energized. As expected from our model calculation, a set of two saddle coils produced 0.36 T in the middle of the coils with a 25 A current at 4 K, which is 63% of the critical current of the wire. The measured homogeneity of the field over the target volume has a maximum variation from the average value of 0.6%.

[en] 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 (π NN) coupling constant (line integral)_π^l

[en] High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPD Gamma experiment, a search for the small parity-violating γ-ray asymmetry A_Y in polarized cold neutron capture on parahydrogen, is one example. For the NPD Gamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized ³He neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 ± 0.5% for neutron energies from 3 to 20 meV over the full phase space of the beam. Systematic effects that the rf spin rotator introduces to the NPD Gamma experiment are considered

[en] The neutron beta-decay lifetime plays an important role both in understanding weak interactions within the framework of the Standard Model and in theoretical predictions of the primordial abundance of ⁴He in Big Bang Nucleosynthesis. In previous work, we successfully demonstrated the trapping of ultracold neutrons in a conservative potential magnetic trap. A major upgrade of the apparatus is nearing completion at the National Institute of Standards and Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89 nm neutrons is incident on a superfluid ⁴He target within the minimum field region of an Ioffe-type magnetic trap. A fraction of the neutrons is downscattered in the helium to energies <200neV, and those in the appropriate spin state become trapped. The inverse process is suppressed by the low phonon density of helium at temperatures less than 200 mK, allowing the neutron to travel undisturbed. When the neutron decays the energetic electron ionizes the helium, producing scintillation light that is detected using photomultiplier tubes. Statistical limitations of the previous apparatus will be alleviated by significant increases in field strength and trap volume resulting in twenty times more trapped neutrons.

[en] The NPDGamma experiment will measure with a high precision, 5x10-9, the small parity-violating gamma-ray asymmetry, Aγ, in polarized cold neutron capture in a para-hydrogen target to determine unambiguously the weak pion-nucleon coupling constant H_π¹. For the experiment the collaboration has built a new high-flux pulsed cold neutron beam line at LANSCE. In 2004, we first commissioned the beam line and then the apparatus with exception of the hydrogen target. The sensitivity of the apparatus was tested by measuring Aγ on Al, B, Cl, Cu, and In. The Cl has a well-known large parity-violating gamma-ray asymmetry that was used to verify the performance of the apparatus. The other nuclei that were studied during the commissioning run are present in materials used for construction of the experiment and are, therefore, possible sources of the false asymmetries since backgrounds are expected to be about 10% of the signal from the neutron capture on hydrogen. We measured Aγ≅0 for these nuclei except for Cl. We report the status of the experiment and preliminary results of the 2004 commissioning run

[en] Parity-odd asymmetries in the electromagnetic decays of compound nuclei can sometimes be amplified above values expected from simple dimensional estimates by the complexity of compound nuclear states. Using a statistical approach, we estimate the root-mean-square of the distribution of expected parity-odd correlations s(vector sign)_n·k(vector sign)_γ, where s(vector sign)_n is the neutron spin and k(vector sign)_γ is the momentum of the γ, in the integrated γ spectrum from the capture of cold polarized neutrons on Al, Cu, and In. We present measurements of the asymmetries in these and other nuclei. Based on our calculations, large enhancements of asymmetries were not predicted for the studied nuclei and the statistical estimates are consistent with our measured upper bounds on the asymmetries