Crystal-field spectroscopy of PuO2: further complications in actinide dioxides

Neutron spectroscopy has been performed on a sample of PuO2, enriched to 94% with the non-absorbing isotope 242Pu, to measure the crystal-field potential. The authors find levels consistent with the weak-field case crystal-field parameters recently derived for UO2 and NpO2, but inconsistent with a weak-field interpretation of the magnetic susceptibility measurements on PuO2. In the light of these discrepancies they believe that the conventional crystal-field model is inadequate. PuO2 is probably the simplest material to test any new ideas because the ground state is a non-magnetic singlet.

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