The modern history of neutron scattering research activities in Japan is reviewed by focusing those at the large experimental facilities of both accelerators and reactors. Now the neutron scattering activities reach the world top class though the history shows a lot of struggles as well as efforts for more than 4 decades. Finally I emphasize here how the Japanese neutron researches go forward with corporate of research development of Japanese materials science.

Recently, accelerator driven neutron sources have become major for neutron experiments. Neutron scattering is most active field in the neutron applications. Furthermore, boron neutron capture therapy (BNCT) is another field recently activated in Japan. Such background accelerated the construction of accelerator driven neutron sources and there already exist neutron sources from compact (～few kW) to large scale (～MW) ones. To produce neutrons various kinds of reactions have been used depending on the accelerated particle energy and type. Here, neutron production reactions and neutron moderator system are introduced, which are used for the accelerator driven neutron sources.

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. Three results obtained by NOVA are introduced.

Neutron scattering experiments including reflectometry have been utilized to analyze the structure and dynamics of polymers and soft matters because neutron beams possess the high penetrating power and high sensitivity to light elements. In this text the basics and experimental examples of neutron reflectometry, which is very powerful to investigate interfaces, are summarized.

Neutron inelastic scattering is a powerful technique to investigate atomic and spin dynamics in condensed matter. Recently developed MW-class accelerator-based spallation neutron source enables efficient data collection in wide momentum (𝘘) and energy (ℏω) space, and is boosting utilization of the inelastic neutron scattering for various condensed-matter systems. In this article, we will overview the neutron inelastic scattering technique from the basic theoretical background to same examples in magnetism research.

Life science is expected to be one of the major subjects of neutron research. The quantum beam properties of neutron, isotope effect and inelastic/quasi-elastic scattering are useful for studying crystal structures, solution structures and dynamic structures of biomolecules. Research on physical properties of biological materials by inelastic scattering is promising as applied research such as food science. The high-intensity pulse neutrons realized by the accelerator not only has developed the life science research so far, but also is opening a gate to the academic field which has never been used before.

Neutron is a nucleon without charge. Because of its unique characteristics, neutrons are used for many kinds of physics researches. Several energies of neutrons, so called fast, epithermal, thermal, cold, and ultra-cold neutrons are applied for different purposes. In this article, I introduce experiments using neutrons for elementally particle, nuclear, and astrophysics with their physics backgrounds: neutron EDM and neutron-antineutron oscillation to solve mystery of matter and anti-matter, neutron lifetime to know how the early universe was, and unknown intermediate force to understand gravity.

RIKEN accelerator-driven compact neutron source (RANS) has been developed and provided neutrons for industrial use. The proton linac of 7 MeV with the maximum average current 100 μA, pulse width 10-180 μs, repetition frequency 20-200 Hz is used with long-life Be target for such practical use in the field of manufacturing. Corrosion in the painted steels are visualized, neutron imaging and neutron diffraction technique have developed with compact neutron source. Non-destructive visualization inside thick concrete slab has been realized for the social infrastructure safety with compact neutron source system.

With increasing concern, and safety consciousness in the global environment, we have been working to develop fuel efficient tire required to achieve two contrary objectives: low fuel consumption performance and high level grip performance. As a contribution to environmental protection, we have focused on the resource savings, and promoted the development of technology of simultaneously improving low fuel consumption performance, grip performance, and wear resistance, which are contradictory to each other. We promoted the combining of J-PARC MLF, SPring-8 and K computer, and achieved the development of new materials to improving tire performances.

Neutron diffraction techniques were used for the studies of battery and related materials. The static crystal structure of super lithium ionic conductors as a solid-state electrolyte are very precious information to improve their lithium conductivity. The highest super lithium ionic conductor, Li₁₀GeP₂S₁₂ was discovered in 2011. Its unknown structure was determined by neutron diffraction. This determined structure was led to the improved materials (Li_9.54Si_1.74P_1.44S_11.7Cl_0.3, Li_9.6P₃S₁₂) which have higher values of the lithium ionic conductivities. Furthermore, a fabricated all-solid-state cell based on the developed lithium conductors showed outstanding battery performances against ones of the current commercialized battery. In addition, an operando diffraction technique on the new developed neutron diffractometer dedicated for battery study in J-PARC, was developed to understand the structural changes of cathodes and anodes during charge–discharge processes in battery. By this technique, relaxation process after a high discharge rate and inhomogeneous structural changes depended on the discharge rates were observed. This information gave new understandings of battery reaction and opened the way for the development of a new advanced battery.

Our daily life highly depends on semiconductor devices such as smart phones. They are also used for social facilities and automotive which must have higher reliability. The soft error has been recognized for these four decades, which is the phenomenon that contents of semiconductor storage elements are flipped by neutron or alpha particles. Since it rarely occurs on the terrestrial region, acceleration tests are mandatory to evaluate radiation hardness. This paper first introduces the single event effects on semiconductor chips. Then soft-error mitigation techniques are explained on process, device and circuit levels. We finally explain how to measure radiation hardness by particle accelerators and conclude this paper.

In recent years, boron neutron capture therapy (BNCT) as a radiotherapy with neutron has attracted attention by recent progress of technology for an accelerator. Several accelerator-based neutron sources for BNCT are being developed in the world. In particular, in Japan, clinical trials of BNCT are being already conducted in a hospital by using the cyclotron-based neutron source for BNCT. Furthermore, some linac-based BNCT devices by combining with different target system and proton energy have been produced, and preparations for clinical trials by using the devices are being progressed.

This is a brief report on the 28^th Linear Accelerator Conference (LINAC 16) that was held at Michigan State University in East Lansing, USA, during September 25-30, 2016. More than 420 participants attended it from seventeen countries and made feverish discussions on various issues, in particular on super conducting hadron linear accelerators. It was followed by the FRIB tour on the last day (Friday) afternoon.