The atomic-beam magnetic-resonance method was used to measure the nuclear gyromagnetic ratios and hyperfine-structure separations of the radioactive isotopes ${\mathrm{Cs}}^{134}$, ${\mathrm{Cs}}^{135}$, and ${\mathrm{Cs}}^{137}$. A surface ionization detector was used.

The hyperfine-structure separations were obtained by direct $\Delta F=\pm 1$ transitions near zero field. The values of $\Delta \nu$ found for the three isotopes are: $\Delta \nu \left({\mathrm{Cs}}^{134}\right)=10\mathrm{}473.626\pm 0.015 \mathrm{Mc}/sec,$ $\Delta \nu \left({\mathrm{Cs}}^{135}\right)=9\mathrm{}724.023\pm 0.015 \mathrm{Mc}/sec,$ $\Delta \nu \left({\mathrm{Cs}}^{137}\right)=10\mathrm{}115.527\pm 0.015 \mathrm{Mc}/sec.$

Pairs of transition belonging to the two different $F$-states, but involving the same $m_F$ values, constitute frequency doublets separated by $2g_I{\mu }_{0}H$. From measurements of the difference frequencies of these doublets for pairs of isotopes in fields in the vicinity of 9000 gauss, the following $g$-value ratios were obtained: $\frac{g_I\left({\mathrm{Cs}}^{135}\right)}{g_I\left({\mathrm{Cs}}^{133}\right)}=1.05820\mathrm{}\pm 0.00008$, $\frac{g_I\left({\mathrm{Cs}}^{137}\right)}{g_I\left({\mathrm{Cs}}^{135}\right)}=1.04005\mathrm{}\pm 0.00008$, $\frac{g_I\left({\mathrm{Cs}}^{134}\right)}{g_I\left({\mathrm{Cs}}^{133}\right)}=1.01447\mathrm{}\pm 0.00029$.

The hfs anomalies arising from the variation of the electron wave function over the finite distribution of nuclear magnetization were calculated from these measurements. The values found for these anomalies, defined by ${\epsilon }_2?{\epsilon }_1=\frac{\left[g_1\Delta {\nu }_2\right(2\mathrm{}{I}_1+1\left)\right]}{[g_2\Delta {\nu }_1\times (2\mathrm{}{I}_2+1\left)\right]}?1\mathrm{}$, are: $\epsilon \left({\mathrm{Cs}}^{133}\right)?\epsilon \left({\mathrm{Cs}}^{135}\right)=+0.037\mathrm{}\pm 0.009\%,$ $\epsilon \left({\mathrm{Cs}}^{135}\right)?\epsilon \left({\mathrm{Cs}}^{137}\right)=?0.020\mathrm{}\pm 0.009\%,$ $\epsilon \left({\mathrm{Cs}}^{133}\right)?\epsilon \left({\mathrm{Cs}}^{134}\right)=+0.169\mathrm{}\pm 0.030\%.$

The theory of Bohr and Weisskopf on the hfs anomalies was applied to these nuclei; the calculations are based primarily on a single-particle model with varying distributions of spin and orbital contribution to the nuclear moment. An apparent magic number effect in the anomalies was observed.

• Received 26 July 1956

DOI: https://doi.org/10.1103/PhysRev.105.590