Imaging phonons in a fcc Pu-Ga alloy by thermal diffuse x-ray scattering

X-ray thermal diffuse scattering intensity patterns from phonons in a fcc delta-Pu-Ga alloy have been recorded using an 18 keV undulator x-ray beam with a beam diameter of 25 mum. The results are consistent with patterns calculated using the Born-von Karman force constant model of lattice dynamics, and support the pronounced softening of the transverse acoustic branch along the [111] direction observed from inelastic x-ray scattering measurements. This work demonstrates the feasibility of using a large-grain, small beam approach to study lattice properties, such as phonon dispersion curves, of materials not readily available in the form of large single crystals. (C) 2004 American Institute of Physics.