Nuclear Hyperfine Structure inEr166

The Mössbauer effect has been used to study hyperfine structure in the 81-keV ($2^{+}$ → $0^{+}$) transition in ${\mathrm{Er}}^{166}$, using Ho${\mathrm{Al}}_2$ as a source. Absorbers of ${\mathrm{Fe}}_2$Er, Er metal, Er${\mathrm{Fe}}_3$Mn, and ${\mathrm{Er}}_2$ ${\mathrm{O}}_3$ were studied with the following results: Magnetic moment of the excited state, 0.61 nm; quadrupole moment, approximately -1.6b; magnetic moment of the ${\mathrm{Er}}^{3+}$ ion in erbium metal at 21°K, 7.5±0.6 μb. The nuclear moments are in good agreement with the values predicted from the collective model, and with other experimental determinations. The resonance absorption is much less than 1%, but the relatively large hyperfine interaction and high counting rates possible make the measurements fairly easy.