Mössbauer studies of ²³⁷Np in a synthetic monazite

The nuclear gamma resonance (NGR) for ²³⁷Np in the compound NpPO₄ has been measured at 4.2 K following the α decay of ²⁴¹Am metal as a source. NGR was also measured in the compound NpO₂ at 4.2 K and 77 K following the α decay of ²⁴¹Am in the compound AmPO₄. In both cases the Np is in a synthetic monazite composed primarily of the compound LaPO₄, an insulator. The isomer shift has been determined from the data and indicates a single charge state for Np in NpPO₄ and multiple charge states for Np following a decay of Am in AmPO₄.