This proposal consists of different sections corresponding to different research areas in which x-ray diffraction is used to investigate basic problems of solid state physics. They propose perform a laser annealing study of silicon, and observe the disappearance of Bragg reflection during melting using a grazing incidence technique in conjunction with time resolved counting. This work is actually in progress. They also hope to determine the radial distribution function of the liquid phase, and to observe the photostriction effect, a lattice contraction during laser illumination due to high density of electron-hole pairs. The mechanisms of sliding Charge Density Waves (CDW's) in a blue bronze crystal will be investigated using a Mossbauer diffraction technique. An experimental investigation on the properties of crystalline Helium is also proposed. Diffraction studies of the electron density of He in the solid state will be carried out, and structural defects will be investigated by means of white beam topography using a synchrotron radiation beam. A project on use of multiple Bragg scattering for solving the phase problem in diffraction, supported by a previous NSF grant, has been brought to completion. Since it represents a major breakthrough in diffraction physics, a full report is given in one section of this proposal.
