Yasumoto Tanaka

1-km beamline at SPring-8

A one-kilometer long synchrotron radiation beamline with an x- ray undulator source was completed at SPring-8. The beamline was planned to facilitate various applications of a wide-area coherent x-ray beam, development of bi-crystal x-ray interferometers for gravitational red-shift measurement and development of highly sensitive diagnostic methods of accelerator dynamics. This paper reports the structure of the long beamline as well as some selected first results including phase contrast imaging and diffraction imaging applications.

Sub-picosecond dynamics in liquid Si

We are the first group to succeed in measuring the dynamic structure factor S(Q,ω) of liquid Si close to melting using high-resolution inelastic x-ray scattering. The spectra clearly demonstrate the existence of propagating short wavelength modes in the melt with a Q–ω relation similar to those in other liquid metal systems. A specific variation of the quasi-elastic line shape with increasing Q is observed close to the structure factor maximum. This observation is related to the onset of atomic correlations on the sub-picosecond timescale in the vicinity of a metal-to-insulator transition. Such observations have been made previously only in computer simulations of metallic systems with increasing covalent character. Our data provide the first experimental evidence for these ultrashort density correlations.

The giant magneto-volume effect in solid oxygen

X-ray diffraction measurements on α-solid oxygen under an applied magnetic field are reported. The volume of α-solid O2 is found to expand with increasing magnetic field: the lattice constants a and b elongate, while the lattice constant c and the angle β are almost independent of the magnetic field. The maximum volume expansion observed is about 1% under a 7.5 T field, which is a giant effect compared to the volume change observed in ferromagnetic metals, such as Fe, Co and Ni. This finding indicates that a spin-dependent inter-molecular potential is essential in determining the structure of α-solid O2. The experimental results conform with predictions based on a magneto-elastic interaction derived from an antiferromagnetic exchange coupling of O2 spins.