PNNL

Abstract

The remarkable magnetic properties of the early actinide dioxides reveal a pronounced sensitiv-ity on the relative energies of low lying electronic states that is not seen in compounds of lighter elements. The complexity of the underlying electronic structure is exemplified by the temperature independent paramagnetism (TIP) of PuO2, which has long proved difficult to explain by conven-tional crystal field theoretical methods. Here we report 239Pu nuclear magnetic resonance (NMR) spectra over temperatures from 11 K to 295 K that reveal features of local magnetism with better than part per thousand resolution. These experiments represent the first independent detection of 239Pu NMR in PuO2 since the original report by Yasuoka and co-workers, and extend the NMR observations to higher temperatures where predictions by recently developed theories of magnetism and spin relaxation may be evaluated. The sensitivity achieved in these experiments was sufficient to measure the sinusoidal dependence of the NMR signal amplitude on the radiofrequency pulse length, which allows the determination of the nuclear g factor and magnetic moment of 239Pu. The results presented here suggest that 239Pu NMR offers a promising new way to study subtle magnetic effects in plutonium materials of both technological and scientific significance.