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College Park, Maryland      June 6 - 10 , 2004

T2-D4 (2:30 PM): Crystal fields in UO2 - revisited

H. Nakotte, R. Rajaram (Physics Department, New Mexico State University, Las Cruces NM 88003), R. McQueeney (Los Alamos Neutron Science Center, Los Alamos National Laboratory), S. Kern (Physics Department, Colorado State University, Fort Collins CO 80524), G.H. Lander (Institute for Transuranium Compounds, D-76125 Karlsuhe, Germany)

Uranium Dioxide (UO2) is an important nuclear fuel material. We performed high-resolution inelastic neutron scattering using PHAROS at the Los Alamos spallation source LANSCE in order to re-investigate the crystal field splitting in UO2, determined with the knowledge of the dipole-allowed transitions. We obtained the crystal field parameters and the 5f electron eigen functions for UO2. The fourth- and sixth-degree crystal field parameters were found to be V4= -116.24 and V6=25.78, in good agreement with previously published results by Amoretti et al. [1]. On the other hand, these previous studies did reveal four crystal-field excitations in the 150 meV to 180 meV range, only three of which can be explained by the crystal-field model. Our experiments on a different UO2 sample show that the previously observed peak at about 180 meV is a spurious one, thus it is not intrinsic to UO2.

[1] G. Amoretti et al., Phys. Rev. B 15 (1989) 1856

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