To investigate the previously reported low-temperature phase transition in rubidium borohydride (RbBH4) near 48.5K, we carried out neutron powder diffraction and vibrational spectroscopy measurements both above and below this temperature on an isotopically-enriched sample of Rb11BD4. Our diffraction data reflected an average cubic Fm3¯m structure with BD4− anion orientational disorder at all temperatures, with no hint of extra Bragg peaks due to long-range orientational order below the transition temperature as reported by others. These structural results and careful analysis of torsional vibrations in RbBD4 corroborate the results of prior neutron vibrational spectroscopy measurements suggesting that the low-temperature RbBH4 structure indeed possesses some orientational ordering of the BH4− anions, but of a shorter-ranged nature insensitive to powder diffraction methods.

Interpreting the spread in equivalent-dose estimates is an important aspect of optically stimulated luminescence (OSL) dating. Ideally, prior to age estimation, an assessment should be made of the likely spread in equivalent dose due to dose-rate heterogeneity in the sediment. Such a procedure would greatly increase the validity of OSL ages, particularly for sediments susceptible to partial bleaching, and for sediments with coarse or poorly sorted grain-size distributions. In this paper we take a step towards a general model of dose-rate heterogeneity by simulating the 40K-derived beta dose to quartz. We present an experimental simulation of the 40K beta dose, and compare the results with a Monte Carlo simulation of the same experiment. The experiment uses artificially produced 24Na to simulate the 40K beta dose to quartz, allowing a large, heterogeneous dose to be administered in a short period of time. The Monte Carlo simulation correctly predicts the shape of the equivalent-dose distribution, but underestimates the spread in dose received by different grains. The experimental set-up provides a new avenue of research into beta-dose heterogeneity.

The details of the rotational dynamics of borohydride ions in both the ordered and disordered crystal phases of NaBH4 and in the disordered crystal phase of KBH4 were determined by quasielastic neutron scattering (QNS). Model fits of the QNS data indicate that the BH4- tetrahedron in the ordered phase of NaBH4 rotates with a combination of 2-site and 3-site reorientations that preserve its crystallographic orientation. The QNS results for the disordered phases are well described by a model assuming nearest-neighbor BH4- jumps from one corner to another of a cube formed by eight hydrogen positions of half occupancy. Distinguishing between likely mechanisms for reorientation was made possible by collecting data at sufficiently high momentum transfer. The activation energies derived for the low-temperature and high-temperature phases of NaBH4 are 13.4 +/- 0.8 and 11.9 +/- 0.5 kJ/mol, respectively. We find an activation energy for KBH4 of 14.6 +/- 0.5 kJ/mol in the high-temperature phase. The torsional vibration bands of both borohydrides were also measured by inelastic neutron scattering.

Solvent extraction was used to prepare pure solutions of 237Np and 233Pa. Portions were used for liquid scintillation counting (disintegration rates) and γ-ray spectroscopy with HPGe detectors. X- and γ-ray intensities observed in the 237Np decay were verified, with a new result of 15.08±0.04% for the 29keV γ-ray (5σ higher than previous reports). K X- and γ-ray intensities observed in the 233Pa decay were verified with new results for the L X-ray intensities (∼55% total L intensity), approximately twice previously reported total intensity.

A stock solution of 238 Np was produced by the 237 Np(n,γ) reaction and was purified by solvent extraction. Three small portions were used to measure absolute activity by liquid scintillation counting, and two large portions were used to obtain γ-ray spectra with Ge detectors. Intensities for strong γ rays (e.g., 25.17±0.13% for 984.17 keV) agree within ∼1% with current evaluations, but several transitions previously assigned to and from the 968-keV level in 238 Pu are unlikely to be present. The β counting yielded a half-life of 2.1024±0.0005 days for 238 Np.