My study on neutron optics started in 1970 when I got the information of the neutron mirrors and the neutron guide tube in the Technical University of Munich. I, however, had limited my neutron optics on the neutron mirrors and the neutron guide tubes until 1985. Since 1990, I have challenged to the neutron spin interferometry together with my collaborators, which include new young physicists too.

During 50 years, I have engaged in the neutron diffraction experiments. We constructed many machines, and produced many researches mainly in the field of magnetism. At the early stage we started our experiment at the old JRR-3 reactor of low neutron flux density. Now, we are using renewed JRR-3 of high flux with low noise. But the reactor is not operated since the disaster 3.11 in 2011. We are eager for JRR-3 to restart.

In this paper, I will report my structural studies for amorphous and nano-crystalline materials by taking advantage of neutron diffraction. Recently, the three dimensional atomic arrangements obtained by reverse Monte Carlo modeling based on neutron and X-ray diffraction data informed us of the precise structural features of amorphous and nano-crystalline materials.

Magnetic field imaging using polarized pulsed neutrons is one of the most attractive applications of the energy-resolved neutron imaging technique. As the interaction between magnetic fields and a neutron spin depends on the neutron wavelength, analysis of the wavelength dependent polarization makes it possible to quantify the both magnetic field strength and direction. Hence, the combination of Time-of-flight method of pulsed neutron beam and three-dimensional polarization analysis is very suitable to the neutron magnetic field imaging technique. In this paper, we will explain about the resent results on magnetic steel sample and on spatial magnetic field from the electromagnet performed at BL10 of MLF in J-PARC.

In general, analysis of quasi-elastic neutron scattering spectra needs some mathematical models in its process, and hence the obtained result is a model dependent. Model-dependent analysis may lead misunderstandings caused by inappropriate initial models or may miss an unexpected relaxation phenomenon. We have developed an analysis method for processing QENS data without a specific model, which we call as mode-distribution analysis. In this method, we supposed that all modes can be described as combinations of the relaxations based on the exponential law. By this method, we can obtain a distribution function B (Q, Γ) which we call the mode-distribution function, to represent the number of relaxation modes and distributions of the relaxation times in the modes. We report the first application to experimental data of liquid water. In addition to the two known modes, the existence of a relaxation mode of water molecules with an intermediate time scale has been discovered.

A stable nanoemulsion consisting of nanometer-sized oil droplets in water having a self-standing capability was prepared by high-pressure emulsification. Rheological measurements show that the nanoemulsion has a high viscosity and a yield stress. Small-angle neutron scattering (SANS) revealed the presence of an ordered crystal-like lattice structure in addition to spherical domains with a diameter of ca. 30 nm. Nonfluidity of nanoemulsion is ascribed to crystal-like lattice structure of nanodroplets. A mixed solution of 2-hydroxyethyl cellulose and the nanoemulsion has shear-thickening behavior (shear-induced gelation). Real-time SANS measurements with a Couette geometry as a function of shear rate (Rheo-SANS) revealed that a possible mechanism of gelation was proposed from the viewpoint of shear-induced percolation transition. Furthermore, mixtures of the nanoemulsion and poly (acrylic acid) solutions were opaque and kept the same interdomain distance and high viscosity. We estimated that it had phase-separated structure between nanoemulsion phase and poly (acrylic acid) solution phase.

We have developed a chopper spectrometer with a pulse-shaping chopper at a pulsed source. In this new type of a spectrometer, tunable and symmetric resolution function can be obtained by shaping the source pulse using an additional chopper (pulse shaping chopper), while keeping high peak intensity of the source. In the course of the development, we investigated and developed design criterions, related devices and other technical and theoretical issues required to realize a double chopper spectrometer. The spectrometer, named AMATERAS, has been finally constructed at Materials & Life Science Experimental Facility at J-PARC, and is producing scientific outputs under J-PARC user program now.

We investigate the doping dependence of the magnetic excitations in the two-superconducting-dome system LaFeAsO_1−xD_x. Using inelastic neutron scattering, spin fluctuations at different wave numbers were observed under both superconducting domes around x =0.1 and 0.4 but vanished at x =0.2 corresponding to the T_c valley. Theoretical calculations indicate that the characteristic doping dependence of the spin fluctuations is rationally explained as a consequence of the switching of the two intra-orbital nestings within Fe-3d_{YZ, ZX} and Fe-3d_X2−Y2 by electron doping. The present results imply that the multiorbital nature plays an important role in the doping and/or material dependence of the T_c of the iron pnictide superconductors.

We have investigated structure and relaxation phenomena for ionic liquids 1-octyl-3-methylimidazolium chloride (C8mimCl), hexafluorophosphate (C8mimPF₆) and bis (trifluoromethylsulfonyl) imide (C8mimTFSI) by means of neutron diffraction and neutron spin echo (NSE) techniques. The diffraction patterns show two distinct peaks appeared at scattering vectors Qs of 0.3 Å^-1 and 1.0 Å^-1. The former originates from the nanoscale structure characteristic to ionic liquids and the latter due to the inter-ionic correlations. Interestingly, the intensity of the low-Q peak drastically grows upon cooling. The NSE measurements have been performed at these two Q positions, to explore the time evolution of each correlation. The relaxation related to the ionic correlation (ionic diffusion) is of Arrhenius-type and exhibits non-exponential behavior. On the other hand, two kinds of relaxation processes, slower and faster ones, are found at the low-Q peak position. The most significant finding is that the fraction of the slower relaxation increases and that of the faster one decreases upon cooling. Combining the NSE data with the diffraction data, we conclude that there exist two parts in ILs; one with the ordered nanostructure exhibiting the slow relaxation, and the other with disordered structure showing faster relaxation.

We review the small-angle neutron scattering (SANS) instruments, prepared at JRR-3, Tokai, Japan. Conventional pin-hole type SANS instruments (SANS-J-II and SANS-U) were recently reinforced by using focusing lens in order to detect ultra-small-angle neutron scattering (USANS) appearing at q=10^-4Å^-1, where q is a magnitude of scattering vector. The double crystal (Bonse-Hart) method is available at PNO instrument which is able to reach to the q-region of q=10^-5Å^-1. mfSANS instrument was designed to reduce its dimension using a focusing method. Dynamical nuclear polarization (DNP) analysis is available at SANS-J-II, in order to perform contrast variation experiments.

The cold neutron beam port C1-3, ULS (ULtra Small angle scattering instrument) has been designed and built for the ultra-small angle scattering using a pair of Si-perfect crystals, neutron interferometry with Si-perfect crystal, double-crystal method to estimate the perfection of crystals. For these years, this beam port is used for the development of neutron interference imaging.

The neutron interference imaging technique has been developed for these years with several methods. These years we are developing neutron interference imaging technique using gratings at ULS. The neutron interference imaging experiment with two absorption gratings has been done. We develop new way to fabricate absorption gratings for neutron with the pitch of 150μm, 180μm, and 200μm. Small break in an acrylic plate was observed.