Experiments on transuranium compounds with X-ray resonant exchange scattering

Synchrotron radiation experiments are reported on single crystals of NpS and PuSb to examine the magnetic structures by using the technique of X-ray resonance exchange scattering (XRES). In the case of NpS the results augment our knowledge of the magnetic phase transition, and, by measuring the ratio of the intensities at the M-5 and M-4 energies we suggest that the electronic configuration of NpS is trivalent Np3+. In the case of PuSb our experiments were unable to observe magnetic scattering. Our interpretation is that an absorbing layer of similar to 1 mu m exists on the surface of the single crystals. No powder diffraction peaks (e.g. from PuO2 or PuSb) could be detected from this layer, indicating that it is either amorphous or small grain. An EXAFS-type analysis shows that the overlayer consists primarily of plutonium and oxygen. We suggest how this may be caused preferentially in the Pu-containing samples because of the alpha-particle activity present in Pu-239. (C) 1999 Published by Elsevier Science B.V. All rights reserved.