PNNL

The Science

The intrinsic radioactivity and unfavorable nuclear properties of actinide isotopes make it distinctly challenging to directly observe their nuclear magnetic resonance (NMR) spectra. In 2012, researchers obtained an NMR spectrum of ²³⁹Pu for the first time. Researchers have finally independently observed and confirmed this finding, acquiring spectra of plutonium oxide (PuO₂) across a wide range of temperatures. The team obtained a revised value for the nuclear g factor of ²³⁹Pu, a fundamental parameter of the isotope.

The Impact

NMR is a fundamental technique for understanding the structural and chemical environment of molecules and materials. However, detection of NMR from open shell metal atoms is exceptionally rare, and in the case of PuO₂, the technical challenge is amplified by the radiological hazard of plutonium. This work demonstrates that ²³⁹Pu NMR is a viable technique to analyze plutonium materials with technological and scientific importance. 

Summary

Studying elements such as plutonium by NMR spectroscopy requires both highly sensitive instruments and facilities capable of handling radioactive materials. Researchers recorded solid-state ²³⁹Pu NMR spectra of crystalline PuO₂ at temperatures from 11 K to 295 K with better than parts per thousand resolution. These experiments represent the first independent detection of ²³⁹Pu NMR in PuO₂ since the original report in 2012 by Yasuoka and co-workers. The results extend NMR observations of plutonium to higher temperatures, enabling the evaluation of recent theoretical explanations of the enigmatic magnetism and electronic structure of PuO₂. The sensitivity achieved in these experiments was sufficient to measure the sinusoidal dependence of the NMR signal amplitude on the radiofrequency pulse length, allowing for the determination of the nuclear g factor and magnetic moment of ²³⁹Pu. These results demonstrate the use of NMR with an open shell f-element and pave the way for explorations of the subtle magnetic effects in plutonium materials with both technological and scientific significance.

Contact

Herman Cho, Pacific Northwest National Laboratory, hm.cho@pnnl.gov 

Funding

This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Heavy Element, Chemistry Program, FWP 73200