High-energy x-rays from a synchrotron radiation source allow us to obtain high-quality diffraction data for disordered materials from ambient to extreme conditions, which is necessary for revealing the detailed structures of glass, liquid and amorphous materials. We introduced high-energy x-ray diffraction beamlines and a dedicated diffractometer for glass, liquid and amorphous materials at SPring-8 and report the recent developments of ancillary equipment. Furthermore, the structures of liquid and amorphous materials determined from the high-energy x-ray diffraction data obtained at SPring-8 are discussed.

The temperature dependence of the x-ray structure factor for SiO 2 glass was measured at several pressures up to 19.2 GPa. The position of the first sharp diffraction peak moved to a higher momentum transfer as the temperature increased in a specific pressure-temperature range. The intermediate range structure was thermally relaxed to a denser one. Around 7 GPa, the temperature-induced shift saturated and the crystallization temperature drastically increased. These results support the existence of a relatively stable high-pressure form of SiO 2 glass. A sudden transformation was not observed.

We report the current status of software development for chopper spectrometers at Materials and Life Science Facility (MLF), the Japan Proton Accelerator Research Complex (J-PARC). Our software, named "Utsusemi", has already been utilized in actual users measurements, while we are proceeding with developments for more effective use of high flux neutrons and event-recording methods.

4SEASONS is a Fermi chopper spectrometer in operation at the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). 4SEASONS is expected to facilitate highefficiency measurements of weak inelastic signals on novel spin and lattice dynamics using thermal neutrons. The spectrometer is equipped with a coupled moderator and sophisticated components such as an elliptical converging neutron guide with high-critical-angle supermirrors, long (2.5 m) position-sensitive detectors, and a Fermi chopper appropriate for multiple-incident-energy (multi-E i ) measurements by the repetition-rate multiplication technique. Herein, we discuss in detail the design and performance of the spectrometer, and present some examples of the measurements obtained using this spectrometer.

We study high-pressure polyamorphism of B2O3 glass using x-ray diffraction up to 10 GPa in the 300-700 K temperature range, in situ volumetric measurements up to 9 GPa, and first-principles simulations. Under pressure, glass undergoes two-stage transformations including a gradual increase of the first B-O (O-B) coordination numbers above 5 GPa. The fraction of boron atoms in the fourfold-coordinated state at P<10 GPa is smaller than was assumed from inelastic x-ray scattering spectroscopy data, but is considerably larger than was previously suggested by the classical molecular dynamics simulations. The observed transformations under both compression and decompression are broad in hydrostatic conditions. On the basis of ab initio results, we also predict one more transformation to a superdense phase, in which B atoms are sixfold coordinated.

We succeeded in experimentally demonstrating that a series of two-dimensional maps of a dynamical structure factor in momentum-energy space with multiple incident energies can be simultaneously obtained by one measurement. This method reduces the dead time of time-of-flight measurement, and thus, it markedly increases the measurement efficiency. Our achievement realized using the Fermi chopper spectrometer 4SEASONS in J-PARC is expected to open up new possibilities of inelastic neutron scattering measurements.KEYWORDS: pulsed neutron source, Fermi chopper spectrometer, inelastic neutron scattering, multi-E i measurement, J-PARC DOI: 10.1143/JPSJ.78.093002A ''Fermi chopper'' spectrometer is a typical instrument for inelastic neutron scattering (INS) measurement at a pulsed neutron source. The Fermi chopper is used for monochromating the incident neutron beam. Inelastic scattering from a sample is measured by a time-of-flight (TOF) technique over a neutron source period. The accumulated TOF data can be converted to a dynamical structure factor. In fact, the INS measurements conducted using Fermi chopper spectrometers have revealed various mysteries of materials science, and thus, a Fermi chopper spectrometer should remain to be a flagship instrument in new-generation pulsed neutron sources such as the Japan Proton Accelerator Research Complex (J-PARC), which is one of the world's highest intensity pulsed neutron sources.A conventional Fermi chopper has a set of curved slits. The curvature is adjusted to the passage of neutrons with a selected velocity, which means that neutron transmission is optimized for a specific single incident energy (E i ). From another point of view, the curved slits would bring about the inefficiency of an INS measurement. Chopper rotation frequency (100 -600 Hz) is typically much higher than the frequency of the pulsed source (25 Hz in J-PARC), and the utilized TOF region of INS measurement with single E i is approximately less than 10% of the source period (40 ms in J-PARC). To reduce the dead time of TOF measurement, we have proposed the method of utilizing multiple E i beams. 1,2)We apply a set of straight and wide slits to a Fermi chopper, and consequently, a high transmission of neutrons can be achieved over a wide E i range, though the energy resolution is relaxed. Thus, this type of Fermi chopper can select multiple E i beams within the source period, and the simultaneous INS measurements with multiple E i 's can be realized. We refer to this method as Multi-E i measurement.Another technique, the so-called ''repetition rate multiplication (RRM) method'', for reducing the dead time of TOF measurement has also been developed, 3,4) and recently its first implementation has been reported. 5) The RRM method is mainly applied to measurements with cold neutrons, such as those involving quasi-elastic neutron scattering. It requires several disk choppers to suppress the contamination of slow neutrons and produce the symmetric pulse shape of incident neutrons. On the other hand, Multi-E i m...

Structural transformation between a dense molecular fluid and a polymeric liquid of phosphorus that occurred at about 1 gigapascal and 1000 degrees C was investigated by in situ x-ray radiography. When the low-pressure fluid was compressed, dark and round objects appeared in the radiograph. X-ray diffraction measurements confirmed that these objects were the highpressure liquid. The drops grew and eventually filled the sample space. Decompressing caused the reverse process. The macroscopic phase separation supported the existence of a first-order phase transition between two stable disordered phases besides the liquid-gas transition. X-ray absorption measurements revealed that the change in density at the transition corresponds to about 40% of the density of the high-pressure liquid.

No abstract