The decay of ${}_{55}{}^{129}{}_{}{}^{}\mathrm{Cs}$ [produced by the ($\alpha ,2n$) reaction on ${\mathrm{I}}^{127}$] has been studied by use of the techniques of scintillation spectroscopy. The half-life of this activity was measured as 32.06±0.06 h. Gamma rays with energies 94, 174, 270, 278, 321, 375, 416, 549, 591, 904, and 945 keV have been observed in the singles and coincidence measurements. The 270-keV gamma ray was observed only in the coincidence measurements. Considerable effort was made to derive accurate energy and intensity information from the spectroscopic data. The electron-capture branching ratios to the ground state and excited states were determined from the coincidence measurements; $log\mathrm{ft}$ values for the various decay branches were derived from these ratios and the gamma-ray intensity measurements. A decay scheme is presented and compared with the pairingmodel calculations of Kisslinger and Sorensen.

DOI:https://doi.org/10.1103/PhysRev.140.B531