NEUTRON INELASTIC EXPERIMENTS ON ACTINIDE DIOXIDES - SEARCH FOR CRYSTAL-FIELD LEVELS IN NPO-2
Early experiments at the pulsed neutron source at ANL showed that it was possible to observe crystal-field (CF) levels at energy transfers above 150 meV in UO-2. More recent investigations at the UK pulsed source at Rutherford Lab. have improved the resolution and seen a series of well-resolved peaks. Based on these measurements the CF parameters are V-4=-130 meV and V-6=30 meV. Since these parameters should be independent of the precise An ion, there is interest in looking at the tetravalent oxides UO-2,NpO-2, PuO-2. We have now performed experiments at ANL on NpO-2 at temperatures between 15 and 200 K. We find no sharp peak at the excitation spectrum up to energy transfers of about 250 meV. This result is contrary to the expected strong transition at about 53 meV using the above CF parameters in a complete intermediate coupling calculation. The observed phonon spectrum of NpO-2, in comparison with that of ThO-2, shows larger widths in all of the three vibrational bands above about 30 meV, which may indicate strong interaction between CF levels with optic phonons in NpO-2.
Bibliographic Reference: 32ND CONFERENCE ON MAGNETISM AND MAGNETIC MATERIALS, CHICAGO, ILLINOIS (USA), NOV. 9-12, 1987 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 33502 ORA
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Record Number: 1989126040001 / Last updated on: 1989-01-01
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