X-ray-absorption studies of krypton precipitates in solid matrices

Krypton K-edge x-ray-absorption spectra have been measured at 300 and 80 K on samples of krypton-implanted Al and Nb foils, graphite, and Grafoil. The near-edge spectra (XANES) at both 300 and 80 K exhibit a white line. Comparisons with the XANES data of bulk solid krypton and spectra amongst different host materials suggest that the krypton in all the implanted hosts precipitates into bubbles at high dosages. The bubbles in Nb hosts are probably all in the solid phase even at 300 K. For Al, graphite, and Grafoil, the bubbles appear to exist in both solid and nonsolid form. The Kr-Kr nearest-neighbor distance in the solid Kr precipitates is estimated from XANES data using an empirical relation deduced from data on bulk solid krypton under high pressure. High pressure within the Kr precipitates is revealed from the smallness of the lattice parameter and the lattice expansion at low temperature. Extended x-ray-absorption fine structure is observed only on a postimplantation thermally annealed Al sample and an as-implanted Nb sample.