SPECTROSCOPIC STUDIES AND CRYSTAL-FIELD ANALYSES OF AM3-SYMMETRY SITEOF THO2( AND EU3+ IN THE CUBIC)

Fluorescence and excitation spectra of Am-3+ diluted in ThO2 are repor ted at room and liquid-helium temperatures along with fluorescence dat a for Eu3+ diluted in ThO2. The Eu3+ data Can be assigned primarily to magnetic-dipole transitions, but the Am-3+ data appear to be primaril y phonon-assisted electric-dipole transitions. Earlier electron-parama gnetic-resonance (EPR) data on Pu-3+ diluted in ThO2 have set limits o n the possible ratios of the crystal-field parameters B-0(4)/B-0(6) fo r this system. Assuming the same ratio should hold for Am-3+-ThO2, the observed transitions were assigned and the values for the crystal-fie ld parameters B-0(4) = -6731 cm-1, B-0(6) = 714 cm-1 were obtained. Th e B-0(4) value is the same order of magnitude as found earlier in inel astic-neutron-scattering experiments for UO2 and NpO2, but B-0(6) for Am-3+-ThO2 is much smaller than determined in the neutron experiments.