The article describes a short autobiography of the author in developing utilization of pulsed neutron technology and science, which was awarded from the Society. His carrier started at Tohoku Electron Linac, then KENS facility, ISIS and ended up at J-PARC realization.

We have been developing a neutron flat panel detector (nFPD) for neutron imaging application. It is based on a new compound semiconductor based FPD coupled with a ZnS/LiF scintillator. The advantage of the FPD is its large area coverage and its usability. In addition, direct optical coupling with the ZnS/LiF scintillator enlarges sensitivity and it is promising technique for the neutron imaging application. We are also testing a new LiNaI₂ (LNI) scintillator.

Neutron transmission spectroscopy is a useful experimental method. A low absorption contribution of neutron allows to observe a scattering contribution in neutron attenuation spectra. A new analysis technique was developed to characterize the contributions of small-angle scattering, magnetic diffraction, and diffraction of liquid from the neutron attenuation spectra. One of the advantages of these techniques is that it is easy to apply them to neutron transmission imaging experiments. The mapping of nanostructures can be achieved with the application of the analysis of the small-angle scattering contribution to the neutron transmission imaging experiments.

A topological insulator is a material that has gapped bulk and conducting edge states due to the difference in topological characteristics between the bulk and the edge. The concept of topologically insulating state has been extended to bosonic quasiparticles, such as magnons and triplons in solids. We demonstrate that triplons construct bands with topologically protected edge states in the spin-1/2 dimerized antiferromagnet Ba₂CuSi₂O₆Cl₂. A bond-alternation of interdimer couplings leads to complex hopping amplitudes of triplons, which leads to non-trivial topology of the bands. A triplon hopping model realized in Ba₂CuSi₂O₆Cl₂ is interpreted as a pseudo-one-dimensional variant of Su-Schrieffer-Heeger (SSH) model, indicating that topologically protected edge states are induced by a bipartite nature of the lattice.

Caloric materials are systems that exhibit significant thermal effects at phase transitions induced by external fields. They can be used for the solid-state refrigeration through a designated cooling cycle. Current caloric materials are characteristic of small isothermal entropy changes of about 50 J kg^-1K^-1, which is one of serious obstacles to the real applications. Recently, we have discovered that plastic crystals exhibit excellent barocaloric effects with typical entropy changes higher than 400 J kg^-1K^-1 induced by a small pressure. While these findings imply the solid-state refrigeration technologies based on caloric materials would be on the horizon, the underlying microscopic scenario on such colossal barocaloric effects has be established by employing in-situ pressure dependent neutron scattering measurements, which also serves as a confirmation of the new finding from the very fundamental origin. The present study might inspire to promote the application of neutron scattering techniques in the future caloric materials research.

The development of drug delivery systems (DDS) that enable encapsulation of drugs, selective delivery to target tissues or organs, and release of drugs has improved therapeutic effect and reduced side effects. DDS carriers are mainly based on the self-assembled nanoparticles, and their size and shape have significant influences on the therapeutic effect and side effects. However, their small sizes preclude from obtaining structural data with high accuracy by using conventional structural analysis techniques. We thus have analyzed the structures of supramolecular assemblies under the same conditions in actual use by neutron and synchrotron radiation small-angle X-ray scattering. Here, we review our recent studies on the structural analysis of supramolecular assemblies, including nanogels and polymer vesicles using contrast-variation neutron scattering and X-ray small-angle scattering measurements.

The performance of cation-conducting solid polymer electrolytes is a key to improving the efficiency of fuel cells and secondary batteries. However, commercial polymers such as perfluorosulfonic acids and polyethylene glycols (PEGs) have drawbacks in stability. On the other hand, polyoxometalates (POMs), which are nano-sized anionic metal-oxygen clusters, can efficiently transport protons, while low durability due to hygroscopicity has been a problem. According to these observations, we have synthesized a series of POM-polymer composites as solid proton conductors to overcome these problems. Spectroscopic studies have shown that the segmental motion of the polymers contribute to the proton conduction. Neutron scattering techniques have revealed that a single PEG chain in the crystalline composite with Keggin-type POM stays as a distorted helix in the nanochannel. While numbers of proton-conducting amorphous POM-polymer composites have been reported, these results show both structure-property relationship and high functionality in POM-polymer crystalline composites.