The general purpose Monte Carlo Particle and Heavy Ion Transport code System (PHITS) is being developed and widely used in various research and development fields, such as nuclear technology, accelerator design, medical physics, and cosmic-ray research. Particularly for the shielding design of neutron scattering instruments at a 1-MW spallation neutron source facility in J-PARC, the PHITS code has been extensively used so far. In order to optimize the shielding design and estimate the dose correctly, we have introduced some special functions to simulate the optical and mechanical devices (supper mirror, T0 chopper), and to reduce the statistical errors of transport particles in the long beam lines (duct source). We present the overview of the PHITS code and show the simulation results of the neutron scattering instruments.
The overview of the recent works by the author at iMATERIA, BL20 of J-PARC MLF is introduced. From the viewpoint of microstructural control, the author and coworkers have expanded the availability of iMATERIA to metallurgical studies. The authors have established the measurement/analysis scheme for crystallographic textures and phase fractions in metallic materials using Rietveld texture analysis. More recently, the authors have developed the in situ measurement environments at high temperatures and under mechanical loading. Thanks to the intense neutron source of J-PARC and the numerous detectors of iMATERIA, dynamic observation of microstructural changes during processing has become possible. This is extensively being used both by academic and industrial researchers.
The data correction and the experimental procedures were upgraded in order to enhance the capability of the pulsed neutron diffractometers at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), and adopted for materials research. The magnetic structure of the intermetallic compound EuGa4 was investigated using the single-crystal pulsed neutron diffractometer SENJU. The diffraction spots from EuGa4 single crystal were clearly observed despite of extremely high neutron absorption of Eu. By adopting a wavelength-dependent absorption collection, the antiferromagnetic structure of EuGa4 with a nearly full magnetic moment of 6.4 μB of Eu was revealed. Further, the stroboscopic neutron diffraction system using the event data recording was developed for the engineering material diffractometer TAKUMI. The domain switching and the lattice strain induced by the intergranular stress in the piezoelectric material in the multilayer actuator under a cyclic electric field were observed with the nominal time resolution of 77 ms.
The present status of the inelasticity correction for liquid and amorphous samples is provided. Although numerous theoretical approaches have been reported, inelasticity correction which can generally be applied to any sample containing large amount of hydrogen atoms has not yet been proposed. We introduce some experimental methods to estimate inelasticity correction curve which can effectively be applied for time-of-flight neutron diffraction experiments.
It is well known that water has anomalous properties compared with other liquids. The anomalies of water arise from the hydrogen bonding network structure. The investigation of the static structure and dynamics over a wide time range by neutron scattering would be useful for elucidation of the origin of the anomalies. In the manuscript, our neutron scattering results for water and aqueous solution are reviewed. (1) Water structure and dynamics confined in mesoporous silica glass. The structure of confined water becomes enhanced without freezing with decreasing temperature. A fragile-strong crossover in the structural relaxation of water is observed at ~220 K. Dynamics of confined water is affected by the properties of the pore wall. (2) Dynamics of water and glycine confined in mesoporous silica glass. Glycine molecules exist near the pore wall at pH=5, whereas they prefer to hydration apart from the pore wall at pH=2. (3) Neutron Brillouin scattering of water. The ratio of the high-frequency sound velocity to the adiabatic one of water is ~2, reflecting the tetrahedral-like water structure. (4) Water structure under high pressure. From the O-O correlation function, it is found that the tetrahedral structure changes to the closed packed one like as simple liquids on compression, indicating that the hydrogen bonds between water molecules are largely bent at 1 GPa.
Bismuth (Bi) has a double-layered structure based on Peierls distortion in crystalline phase. Complicated static structure in liquid phase which cannot be interpreted by a simple packing model has been conjectured that Peierls distortion may remain even in liquid phase. We measured quasi-elastic neutron scattering (QENS) of liquid Bi by using AMATERAS installed at BL14 beamport of Materials and Life Science Experimental Facility (MLF) in J-PARC and analyzed coherent QENS spectra. A time-space correlation function revealed that the nearest neighboring shell followed by a shoulder-like structure at longer side consists of four contributions of short and long correlations with relatively long relaxation time of a few tens pico second and medium-ranged and the longest correlations with a short relaxation time of sub-pico second, which is a direct observation of the existing layered structure in liquid Bi. In this article, we report the above scientific results and the method to analyze coherent QENS by the time-space correlation function.
Mixing states of imidazolium-based ionic liquids, 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide and nitrate (CnmimTFSA and CnmimNO3, respectively, n gives the alkyl chain length) with various molecular liquids, such as methanol, benzene, and water, have been elucidated on both mesoscopic and microscopic scales using SANS, infrared (IR), and NMR techniques. In many cases, where the interactions between ionic liquids and molecular liquids are not strong, both liquid molecules may form clusters. On the contrary, as the interactions are strong, both liquid molecules are homogeneously mixed with each other at least on the SANS scale.
Nano-confined water (“water pocket”) was realized in ionic liquid. Static structure of the water pocket was examined by a complementary use of small angle X-ray and neutron scattering. The size of the “water pocket” was evaluated to be 20 ~ 30 Å and varied depending on temperature and water concentration. Dynamics of the water pocket was obtained by quasielastic neutron scattering (QENS). Compared with the bulk water, slow water diffusion in the water pocket was clarified by the QENS.