The nanometer-sized metals attract much attention since their physical and chemical properties are substantially different from those of bulk metals. In this work, neutron powder diffraction experiments on the nanoparticles of palladium deuteride, which is the most popular metal hydride, have been performed at 300, 150, and 44 K to investigate the position of the deuterium atoms in the fcc lattice of Pd. The Rietveld analysis revealed that D atoms are located at the tetrahedral (T) sites in addition to the octahedral (O) sites. This is in contrast to the result that only the O sites are occupied in bulk Pd and in other transition metals with the fcc lattice at ambient pressure and temperature. We guess that the T site occupation is due to the change in potential energy caused by the surface and/or distortion effects of nanoparticles.
Single crystal neutron diffractometer is a powerful tool for elucidating the hydrogen and proton structures of biological macromolecules. We developed and employed a profile fitting method for the peak integration of neutron time-of-flight diffraction data collected by the IBARAKI Biological Crystal Diffractometer (iBIX) at the Japan Proton Accelerator Research Complex (J-PARC) for ribonuclease A single crystal. In order to determine proper fitting functions, four asymmetric functions were evaluated using strong intensity peaks. A Gaussian convolved with two back-to-back exponentials was selected as the most suitable fitting function, and a profile fitting algorithm for the integration method was developed. The intensity and structure refinement data statistics of the profile fitting method were compared to those of the summation integration method. It was demonstrated that the profile fitting method provides more accurate integrated intensities and model structures than the summation integration method at higher resolution shells. The integration component with the profile fitting method has already been implemented in the iBIX data processing software STARGazer and its user manual has been prepared.
Hydrogen is the most abundant element in the solar system and is considered to be one of the promising candidates of the light elements in the Earth’s core. However, the amount of hydrogen dissolved in the core and its process are still unknown because hydrogen cannot be detected by X ray and easily escapes from iron at ambient conditions. In this study, we have conducted high-pressure and high-temperature in-situ neutron diffraction experiments on the iron-hydrous mineral system using PLANET in J-PARC. We observed that the water, which was dissociated from a hydrous mineral, reacted with iron to form both iron oxide and iron hydride at about 4 GPa. Iron hydride remained stable after further increase in temperature. This formation occurred at 1000K, where no materials melted. This suggests that hydrogen dissolved into iron before any other light elements dissolved in the very early stage of the Earth’s evolution.
A various kinds of radioactive neutron sources have been developed since neutron had been first discovered. The reactions which are mainly taken advantage for generating neutrons as radioactive neutron source are (α,n) reaction, (γ,n) reaction and nuclear fission reaction. Only 241Am-Be and 252Cf neutron sources are now available due to reliable reproducibility of neutron emission, long half-lives and less disturbing gamma ray emission. Both are designated as a “reference neutron source” by ISO 8529 series describing principle of establishment of neutron calibration field. Total neutron emission rate from neutron source must be well defined in terms of sophisticated method by national metrological laboratory. In order to serve a reliable neutron calibration field produced by a RI neutron source, correction factor for anisotropic emission from cylindrical-shaped neutron source must be experimentally determined for neutron fluence rate at a point of test in the calibration laboratory.
This review reports an overview for DT/DD fusion based neutron sources, such as sealed portable neutron generators employing solid-targets, portable neutron generators based on inertial electrostatic confinement of plasmas, and relatively large stationary devices employing either solid- or gas-target with higher intensities. Though less intense than accelerator based neutron sources making use of other nuclear reactions, the DT/DD fusion based compact neutron sources with typically <1 m in length and <20cm in diameter are useful for some specific purposes with their distinct advantages such as portability, minimal gamma-ray byproducts, ability to provide mono-energetic neutrons, and tagged neutrons enabling three-dimensionally spatial resolved analyses. A next generation gas-target based volumetric neutron source has been proposed to extend its capability of neutron yield in excess of 1015 neutrons/sec in a compact configuration ~6 m in length for application to testing fusion reactor materials.