Unperturbed and perturbed angular correlation and conversion electron measurements have been performed to obtain spectroscopic information on the low-lying levels of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ fed by the decay of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Cs}$. We established $I^{\pi }\left(318\mathrm{}\mathrm{keV}\right)={\frac{3}{2}}^{+}$, $I^{\pi }\left(411\mathrm{}\mathrm{keV}\right)={\frac{1}{2}}^{+}$, $I^{\pi }\left(589\mathrm{}\mathrm{keV}\right)={\frac{3}{2}}^{+}$, $\delta \left(39.6\mathrm{}\mathrm{keV}\right)=-(2.6\mathrm{}\pm 0.5)\times {10}^{-2\mathrm{}}$, $\delta \left(177\mathrm{}\mathrm{keV}\right)=0.44\mathrm{}\pm 013$, $\delta \left(372\mathrm{}\mathrm{keV}\right)=+0.97\mathrm{}\pm 0.09$, $\mu \left(39.6\mathrm{}\mathrm{keV}\right)=+(0.88\mathrm{}\pm 0.26){\mu }_N$. $B\left(M1\mathrm{}\right)\mathrm{}$ and $B\left(E2\mathrm{}\right)\mathrm{}$ values are derived from above data and earlier lifetime determinations. A weak-coupling calculation is presented to explain experimental data.

RADIOACTIVITY ${}_{}{}^{129}{}_{}{}^{}\mathrm{Cs}$ [from $I(\alpha ,2n)$]; measured $\mathrm{ce}\frac{K}{L}$, $\gamma \gamma \left(\theta \right)$, deduced $I$, $\delta$, $B\left(E2\mathrm{}\right)\mathrm{}$, $B\left(M1\mathrm{}\right)\mathrm{}$. Measured $\gamma \gamma (\theta ,H)$, ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ level deduced $g$. Ge(Li), Si(Li) detectors. Isotopically separated source.

• Received 29 January 1974

DOI:https://doi.org/10.1103/PhysRevC.10.402