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Radioactive Resonance
Nuclear magnetic resonance (NMR) spectroscopy and its spatially sensitive cousin, magnetic resonance imaging, have found widespread application in chemical and biological characterization studies. For the most part, these studies take advantage of the energy bifurcation manifested by hydrogen nuclei with oppositely directed spins in a strong magnetic field. More generally, many heavier elements manifest the same effect—including carbon-13, fluorine, and phosphorus. In theory, researchers have known for 50 years that plutonium nuclei have a net spin conducive to NMR. Yasuoka et al. (p. 901; see the Perspective by Albrecht-Schmitt) have now at last observed the resonance of the Pu-239 isotope in a sample of plutonium dioxide.
Abstract
In principle, the spin-½ plutonium-239 (239Pu) nucleus should be active in nuclear magnetic resonance spectroscopy. However, its signal has eluded detection for the past 50 years. Here, we report observation of a 239Pu resonance from a solid sample of plutonium dioxide (PuO2) subjected to a wide scan of external magnetic field values (3 to 8 tesla) at a temperature of 4 kelvin. By mapping the external field dependence of the measured resonance frequency, we determined the nuclear gyromagnetic ratio 239γn(PuO2)/2π to be 2.856 ± 0.001 megahertz per tesla (MHz/T). Assuming a free-ion value for the Pu4+ hyperfine coupling constant, we estimated a bare 239γn/2π value of ~2.29 MHz/T, corresponding to a nuclear magnetic moment of μn ≈ 0.15μN (where μN is the nuclear magneton).
