No abstract

Neutron spectroscopy has been performed on a sample of PuO,. enriched to 94% with the non-absorbing isotope 242Pu, to measure the crystal-field potential. We find levels consistent with the weak-field case crystal-field parameters recently derived for U 0 2 and N p 0 2 , but inconsistent with a weak-field interpretation of the magnetic susceptibility measurements on PuO,. In the light of these discrepancies we believe that the conventional crystal-field model is inadequate. PuO, is probably the simplest material to test any new ideas because the ground state is a nonmagnetic singlet.

The structure of the (-phase in the Pu-U system has been determined by neutron powder diffraction. The phase crystallizes in space group R3m with 58 atoms in the primitive unit cell and 10 atoms in the asymmetric unit. The structure is characterized by many short bonds and fits the general pattern of the light actinides. Thermal expansion and elastic data were obtained from the diffraction experiments.

We have been using time-of-flightneutron powder diffractionto determine the Debye-Waller factorsof the lightactinideelements. The Debye-Wallerfactor isa measure of the mean-squareatomicdisplacementthatarisesfromthe thermalmotionof the atomsin any solid. Its temperaturedependencedeterminesa Debye-Wallertemperature,®DW,that is characteristic of the elasticpropertiesof the solid.The data are obtainedby Rietveld

No abstract