NUCLEAR MOMENT RATIOS IN 237NP FROM MOSSBAUER SPECTRA

Hyperfine structure has been observed in Mössbauer spectra of the 59.54-keV ray of Np237 in NpAl2 and NpCl4. At 77°K, NpAl2 gave an unsplit absorption line; at 4.2 and 2.35°K, magnetic hfs extending over 18 cm/sec was observed. The partially resolved spectrum of NpCl4 at 77°K was interpreted as pure quadrupole splitting; at 4.2°K, combined magnetic and quadrupole interactions were found. From these spectra, the following ratios were determined between the 59.54-keV level and the ground state of Np237: quadrupole-moment ratio +1.00.1; magnetic-moment ratio +0.5370.005. Nuclear polarization in the Mössbauer spectra of NpAl2 at 4.2 and 2.35°K enabled the magnetic-moment ratio to be determined uniquely. The results agree with theoretical predictions of the collective model if the odd-nucleon g factor is quenched to about 70% of the free-proton value. From a comparison of the present work with earlier measurements, a new estimate for the Np237 ground-state magnetic moment is 2.8 nm. © 1968 The American Physical Society.