Polymer gels are functional soft materials with high-water absorbency and good affinity to various kinds of solutes, such as foods, cosmetics, and medicines. Because of these characteristic features, gels have been used in daily life over the centuries. Due to their complicated network structures, however, polymer gels have been recognized as messy systems in chemistry and physics. However, the discovery of volume-phase transition of gels in 1978 shed a light on gels. Polymer gels became one of the most topical themes in soft-condensed matter physics. Another aspect of gels is their fragility. Because of it, gels have not been applied to constructional materials. In the beginning of this century, however, several types of super-tough polymer gels were discovered and developed especially in our country. Now, polymer gels have various potential applications not only to foods and cosmetics but also to bioengineering tissues, medicine, and even to constructional materials. In order to understand and improve the properties of gels, it is essential to investigate the structure of gels. I have been devoted in structural characterization of polymer gels with neutron scattering during the last three decades. This article reviews neutron scattering studies on polymer gels together with micelles from a personal viewpoint.

Multilayer mirror is very useful reflective device for slow neutron experiments. Recently, we succeeded in fabrication of large size neutron supermirror with high reflectivity using ion beam sputtering system (KUR-IBS) and of all neutron supermirrors in two neutron guide tubes at BL06 at J-PARC MLF. We also realized large size flexible self-standing m=5 NiC/Ti supermirror. In this paper, we overview the performance and utility of neutron multilayer mirrors fabricated with the KUR-IBS.

  Bio-molecular dynamics should be characterized with wide time-space ranges. Incoherent neutron scattering is the powerful method to observe the dynamics in THz region, which is essential for the solvent-coupled dynamics. Furthermore, this method is sensitive to the hydration water dynamics. The incoherent scattering gives auto-correlation function of a single atom, therefore, information of the molecular structure is lost in this kind of neutron experiment. The molecular dynamics simulation is effective for analysis and interpretation of the experimental data. We have shown that the protein dynamical transition is coupled with the fluctuation of the hydration water network on protein surface, and that DNA dynamics is sequence dependent, by incoherent neutron scattering and molecular simulation.

Neutron reflectometry (NR) is one of the powerful tools to investigate surface and interfacial structures of materials in the spatial range from nm to sub-μm. Because hydrogen and deuterium atoms have different scattering length for neutrons, NR can distinguish deuterated materials from hydrogenated ones in the mixture of soft-condensed matters, such as polymer blends, bio-mimic membranes, and so on. Additionally, in-situ NR measurements of a solid/liquid interface can be easily realized because neutron can illuminate the interface through the substrate owing to the high transmissibility. In J-PARC/MLF, a horizontal type reflectometer SOFIA at BL16 has been developed. In this paper, a design of the systems, data acquisition and reduction software, sample environments, and future plans to upgrade the SOFIA reflectometer are introduced.

Since the discovery, research on iron-based superconductivity (SC) has become one of main streams in condensed matter physics. The interplay between structure, magnetism and SC is one of most intriguing subjects of this field. To gain further insight into the mechanism of the SC and variation of magnetic orders, investigation of Fe-based compounds with a separate spatial dimension is important. This is because the dimensionality should influence magnetism and can control itinerancy of electrons by changing Fermi surface topology. Here we report our recent studies of iron-based two-leg ladder compounds AFe₂X₃ (A = Rb, Cs, Ba; X = S, Se). Unlike most of parent compounds of the Fe-based SCs, the ladder compounds are insulating down to low temperatures. Through bulk properties and neutron diffraction measurements, a variety of magnetic structure and low-dimensional characteristics were elucidated. These would provide a clue for understanding of the iron-based SC.

On the occasion of my retirement, some memories of my research life with neutron scattering experiment are described.

The standard model of particle physics is the most successful theory. Since, however, it cannot explain the generation process of the matter/antimatter in the universe and cannot unify the gravitational force, many scientists are going to solve the problem. The neutron, the smallest chargeless baryon, is a unique particle and used to investigate such researches. BL05/NOP is a beamline for fundamental physics experiments using novel neutron optics techniques. This beamline is divided into three branches by beam benders; Unpolarized beam branch provides most intense beam and equips a Doppler shifter to use ultra cold neutrons. Polarized beam branch provides larger polarized beam and equips a spin flip chopper. Low-divergence beam branch provides high luminosity beam. In this paper, specification of the beamline and each branch are introduced.

High intensity neutron total diffractometer (NOVA) was installed at BL21 of J-PARC/MLF and achieved the designated level of performance to study atomic distribution in various materials including liquids, amorphous and crystals. Short time and small sample measurements are feasible for averaged structure analysis, and the real space resolution is enough for local structure (Pair Distribution Function) analysis. Sample environments were prepared for auto sample change, low/high temperature and gas pressure, and time-transient hydrogen absorbing process was observed with the in-situ hydrogen pressure measurement system.

Engineering Materials Diffractometer (TAKUMI) operated at MLF in J-PARC is presented. TAKUMI is pulsed-neutron powder diffractometer, in which two detector banks are placed at 90 degree position of scattering angle. This enables simultaneous measurement about both the radial and axial direction of the sample. It was designed to apply to wide range of engineering researches and has been used since 2009. Because of high penetration of neutron, various kinds of experiments using bulk sample or sample environment such as loading, high temperature, low temperature, etc. have been performed. Some examples obtained by using TAKUMI, such as residual stress measurement and in-situ observation of deformation under loading are described.

Single crystal neutron diffractometer is a powerful tool to obtain the structure and magnetic information of various materials including the light elements. Two single crystal time-of-flight neutron diffractometers have been newly constructed at the Materials and Life Science Experimental Facility (MLF), J-PARC. One is IBARAKI biological crystal diffractometer called iBIX dedicated for structural biology and chemistry. The other is extreme environment single crystal diffractometer called SENJU for solid state physics and chemistry field. A brief introduction, specification of these diffractometers and examples of experimental results by using them are reported in this paper.