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Transport behavior of monovalent and divalent solutes across mesoporous Anopore γ-alumina membranes was investigated as a function of pore diameter, pH, ionic strength, and nature of the salt or complexing species in solution. Radiotracers 137 Cs, 85 Sr, 22 Na, and 45 Ca were present in the feed solutions at very low concentrations, ranging from 10 -9 to 10 -12 M and total salt concentrations from 0.1 to 10 -4 M. The divalent cations Ca 2+ and Sr 2+ exhibit lower diffusion rates (3-7 times slower) than the monovalent cations Cs + and Na + for membranes with 20 nm diameter pores. Differences between monovalent and divalent cation diffusion rates for the membranes can be explained in terms of a Donnan exclusion effect from the positively charged alumina surface. The rate of Sr 2+ transport across the 20 nm alumina membranes was greatly increased by raising the pH (reducing the membrane surface charge) from 5 to 8 for both the feed and receive sides. Increased ionic strengths and the addition of complexing agents or specific salt solutions also facilitated divalent ion transport. Diffusion coefficients for divalent cations increased 3-fold for the 100 nm pore diameter membranes.

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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).