Decay ofCs129andI131to the Levels inXe129andXe131

The decay schemes of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Cs}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{I}$ have been investigated using Ge(Li) and Si(Li) semiconductor detectors as well as various coincidence techniques. Gamma-ray energies and relative gamma-ray intensities were determined as well as conversion coefficients for many transitions. In ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$, levels at 322.0 and 904.9 keV were proposed, which have not been reported earlier. The spin and parity assignments for the 332.0-keV level are probably $\frac{5}{2}$+. In ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$, a level at 404.8 keV has been found which was not previously known. The spin and parity assignments for this level are ½+ or $\frac{3}{2}$+. Beta-gamma coincidence measurements were used to indicate that the 503-keV $\gamma$ ray in ${}_{}{}^{131}{}_{}{}^{}\mathrm{I}$ decay feeds the 11/2-isomer of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$. Decay schemes for both ${}_{}{}^{129}{}_{}{}^{}\mathrm{Cs}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{I}$ consistent with our observations have been constructed. The levels of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ and ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ are compared with each other and with current theoretical calculations.