A study has been made of the nuclear spins $I$ and hyperfine structures of several radioactive isotopes in the rare-earth region. The nuclear-spin determinations are ${\mathrm{Pr}}^{143}(I=\frac{7}{2})$, ${\mathrm{Nd}}^{149}(I=\frac{5}{2})$, ${\mathrm{Tb}}^{161}(I=\frac{3}{2})$, ${\mathrm{Ho}}^{161}(I=\frac{7}{2})$, and ${\mathrm{Er}}^{165}(I=\frac{5}{2})$. The measured hyperfine constants are: for ${\mathrm{Er}}^{171}$, $\mathrm{}\left|A\right|=197.0\mathrm{}\left(2.9\right)\mathrm{}$ Mc/sec, $\mathrm{}\left|B\right|=3646\mathrm{}\left(106\right)\mathrm{}$ Mc/sec, $\frac{B}{A}>0\mathrm{}$; and for ${\mathrm{Tm}}^{171}$, $\mathrm{}\left|A\right|=372.1\mathrm{}\left(5.9\right)\mathrm{}$ Mc/sec; and the moments inferred from them are: for ${\mathrm{Er}}^{171}$, $\left|{\mu }_I\mathrm{}\right|=0.70\left(5\mathrm{}\right)\mathrm{}$ nm, and for ${\mathrm{Tm}}^{171}$, $\left|{\mu }_I\mathrm{}\right|=0.227\left(5\mathrm{}\right)\mathrm{}$ nm. A discussion of these values in terms of the various nuclear models is included.

• Received 30 April 1964

DOI:https://doi.org/10.1103/PhysRev.135.B1281