Crystal structures of iron-based superconductors are introduced. Powder neutron diffraction measurements reveal that their crystal structure and superconductivity are strongly correlated. Superconducting transition temperature (T_c) attains a maximum value when FeAs₄ or Fe(Se,Te)₄-Tetrahedrons form a regular shape. Based on this relationship, we have performed high-pressure resistivity experiments on FeSe_0.5Te_0.5, which has the simplest crystal structure in iron-based superconductors. T_c increased rapidly from 14 K to 26 K upon applying pressure up to 2 GPa and we clarified the pressure-induced phase transition from superconducting to metallic phase on the P-T_c phase diagram for the first time.

Development of position-sensitive scintillator detectors and a ³He gas-based micro-pattern neutron detector for the J-PARC/MLF was briefly reviewed. The two types of scintillator detectors: the two-dimensional detector for the iBIX and the one-dimensional detector for the Takumi, were successfully developed. The manufacturing technologies of these detectors were transferred to the industry. The beam line detectors, 14 for the iBIX and 10 for the Takumi, were delivered to the J-PARC/MLF and they have been in service since April 2009. Development of the ³He gas-based neutron image detector with individual read out is in progress. The performance of the detector employing a micro-pixel sensor is presented.

HIV-1 protease is an aspartic protease, and plays an essential role in replication of HIV. To develop HIV-1 protease inhibitors through structure-based drug design, it is necessary to understand the catalytic mechanism and inhibitor recognition of HIV-1 protease. We have determined the crystal structure of HIV-1 protease in complex with KNI-272 to 1.9 Å resolution by neutron crystallography in combination with 1.4 Å resolution X-ray diffraction data. The results show that the carbonyl group of hydroxymethylcarbonyl (HMC) in KNI-272 forms a hydrogen bonding interaction with protonated Asp 25 and the hydrogen atom from the hydroxyl group of HMC forms a hydrogen bonding interaction with the deprotonated Asp125. This is the first neutron report for HIV-1/inhibitor complex and shows directly the locations of key hydrogen atoms in catalysis and in the binding of a transition-state analog. The results confirm key aspects of the presumed catalytic mechanism of HIV-1 protease and will aid in the further development of protease inhibitors.

Neutron visual sensing techniques are powerful and attractive advanced techniques for many kinds of scientific and industrial fields. In this article, the followings are described; (1) attractive points, (2) development of neutron visual sensing techniques at JAEA by now, (3) some applications, (4) prospects for future and (5) problems for the spread. The high-speed 2D method, high-speed scanning 3D/4D CT method, and multi-beam 4D CT method which have been developed by JAEA are reported. Visualization of oil flow in a mortaring car engine by the high-speed 2D method and 4D view of the falling sand flow in sand glasses by the high-speed scanning 4D CT method, which are carried out using JRR-3, are shown as application samples. Now, we run toward the development of the advanced pulse neutron visual sensing techniques for the multi-purpose applications using J-PARC as the pulse neutron source.

For inelastic pulsed-neutron scattering experiments, we developed a Fermi chopper by using the rotation system of a turbo molecular pump with a magnetic bearing system. The frequency resolution of 0.1 Hz was confirmed at 600 Hz, this indicates that a Fermi chopper can be realized with a reasonably good performance in this system.

Continued from the previous number, engineering diffractometer specialized to make stress measurement and material characterization in JAEA is reported. There are three engineering diffractometers in JAEA: two of those are RESA and RESA-II at JRR-3 reactor, and one another is a new diffractometer, TAKUMI, at a pulsed source in J-PARC. In this present number, the outline of instrumentation and the most elementary points of experimental technique on neutron stress measurement are explained.

We have been studied on amphiphilic polymer monolayer structure at the air/water interface by X-ray and neutron reflectometry. By complemently use of X-ray and neutron reflectometry, we have found (1) the existence of carpet layer in ionic polymer brush in monolayer system and (2) characteristic structural change in polymer/subphase interface. Furthermore, interesting experiment on small ion distribution was carried out by NR with contrast variation method. With our experimental examples, characteristic points in the neutron reflectivity measurement at the air/water interface and further possibility in this research area are discussed.

Grazing incident small angle scattering has been used for the analysis of surface and thin film structures. X-ray in particular is widely used for such analysis and called grazing incident small angle X-ray scattering (GISAXS). However, a very limited number of studied has been done using grazing incident small angle neutron scattering (GISANS) primarily due to low intensity of neutron beam. The arising JPARC neutron source will enable us to use GISANS to analyze thin film structures of softmatter. This report provides a basic concept of GISAS using an example of the analysis of nanocellular thin films fabricated by block copolymer template with supercritical carbon dioxide (BSTSC).

An introduction to neutron detectors that includes neutron detection principle, detector types, and how to choose a detector is described.