237Np Mössbauer spectroscopy on neptunium doped borosilicate glasses

Mössbauer and magnetization measurements have been carried out on borosilicate glasses containing neptunium. Different melting and annealing times, in various crucibles have been investigated. Using the 59.5 keV Mössbauer resonance in²³⁷Np we have characterized valency states of neptunium ions in glasses and studied hyperfine interactions. Roughly, absorption spectra show two sites easily differenciated above 50 K by two lines. Isomer shifts (relative to NpAl₂) are respectively: – 10.0 (1.0) and + 32.5(.5) mm/s. These resonance lines can be assigned, the first at Np⁴⁺, the second at Np³⁺ species. The intensity ratio Np⁴⁺/Np³⁺ varies with elaboration conditions. At 4.2 K, Np⁴⁺ ions exhibit a hyperfine splitting arising from relaxation phenomenon. Magnetization measurements do not show any magnetic ordering.