Observation of ²³⁹ Pu Nuclear Magnetic Resonance

Abstract

In principle, the spin-½ plutonium-239 ((239)Pu) 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 (239)Pu resonance from a solid sample of plutonium dioxide (PuO(2)) 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 (239)γ(n)(PuO(2))/2π to be 2.856 ± 0.001 megahertz per tesla (MHz/T). Assuming a free-ion value for the Pu(4+) hyperfine coupling constant, we estimated a bare (239)γ(n)/2π value of ~2.29 MHz/T, corresponding to a nuclear magnetic moment of μ(n) ≈ 0.15μ(N) (where μ(N) is the nuclear magneton).

Microscopic theory of the insulating electronic ground states of the actinide dioxides AnO2(An = U, Np, Pu, Am, and Cm)

“…26 A recent Pu-NMR study confirmed the nonmagnetic character of the ground state of PuO 2 . 18 In AmO 2 a clear antiferromagnetic-looking phase transition is observed at 8.5 K, 15 however, no magnetic moment has been observed in Mössbauer nor in neutron scattering measurements. 16,17 The fingerprint of this dioxide is similar to the one obtained in earlier studies of NpO 2 , and hence, an AF-MPO state is expected in AmO 2 .…”

“…8,9 AmO 2 undergoes a conspicuous phase transition at around 8.5 K. 15 While a peak structure in the magnetic susceptibility was found, 15 neutron-diffraction measurements could not detect antiferromagnetic order in agreement with the Mössbauer measurement. 16,17 PuO 2 is a simple nonmagnetic insulator, 18 whereas CmO 2 has an unexpected paramagnetic moment. 19 Surprisingly, each of these actinide dioxides is an insulator, in spite of the very different emerging orders and physical properties.…”

Ferromagnetic ordering in NpAl2: Magnetic susceptibility and Al nuclear magnetic resonance

“…For the actinide series two nuclei are of practical use, namely 235 U [3,4] (I¼ 7/2) and 239 Pu [5] (I ¼1/2), but unfortunately only at very low temperatures because the very fast spin-lattice relaxation rate makes the signal vanish quickly with increasing temperature (e.g. no signal was detected above 14 K for 235 U).…”

“…no signal was detected above 14 K for 235 U). Few installations exist around the world where NMR studies can be carried out on nuclear materials [5][6][7][8][9][10]. Here, we focus on a model compound and examine its magnetic properties by magnetization, susceptibility, and low-temperature NMR measurements.…”

Magnetic Structure of UO2 and NpO2 by First-Principle Methods

“…1 For instance, multiple DFT calculations have indicated an AFM ground-state, which contrasts with the DM state established by experimental methods. [107][108][109][110] The mechanisms behind such an intriguing electronic states are not yet fully understood and the crystal and magnetic structures of NpO2 have still not been resolved.…”