Neutron diffraction and EXAFS measurements, and the detailed structural modeling by reverse Monte Carlo simulation have been performed in order to study the short-and intermediate-range structures of liquid Rb-Se mixtures. The Se chains in the liquid mixture are strongly bent to form horseshoe-like Se chains with Rb atoms at the chain ends, creating a large amount of voids. The interaction between Rb and Se atoms is weak and Rb atoms come close together. Near the boundary of the miscibility gap at low temperature the short Se chains link up to form a large cluster, and Rb atoms sit around it. The structure factor S(Q) in the liquid mixture has a small pre-peak at 1.3Å^-1. The computed partial S_ij(Q) for the RMC model indicates that the pre-peak is associated with the Se-Se interchain component of S(Q). From the void analysis using Delaunay simplices it has been revealed that the observed pre-peak corresponds to a pre-peak in the concentration-concentration structure factor due to the chemically ordered packing of the voids and Se chains in the structure.

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Methane hydrate has attracted great interest as an energy resource to replace natural gas since this material is deposited in the seafloor and the deposits are estimated to exceed those of natural gas. Understanding the physical proprieties, such as the temperature dependence of the crystal structure, helps to specify the optimum environmental temperature and pressure during drilling, transport, and storage of methane hydrate. Clathrate hydrates consisted of encaging atomic and/or molecular species as a guest and host water formed by a hydrogen bonding. Although many studies on the clathrate hydrate including methane hydrate were reported, no detailed crystallographic property has yet been cleared. We focused on the motion of methane in the clathrate hydrate by the neutron diffraction. The crystal structure of the methane hydrate was analyzed by the applying the combination of the Rietveld refinement and the maximum entropy method (MEM) to neutron powder diffraction. Temperature dependence of the scattering-length density distribution maps revealed that the motion of methane molecules differs between the shapes of dodecahedron and tetrakaidecahedron.

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We present the reconstruction of T2-3 beam port in the guide hall of JRR-3. A new T2-3 is a multi-purpose thermal neutron beam port, named “MUSASI” with two monochromatic beam used for extreme condition experiments under high fields or at ultra-low temperatures, development and performance tests of neutron detectors and optical devices for J-PARC, and industrial use such as residual stress analysis, etc. A sufficient beam time in a unit of 25 days is provided for internal and outside users. We request neutron community to join this project and suggestion/criticism aimed to effective use of this beam line, oriented to complementary use of JRR-3 with J-PARC.

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