Decay Scheme of 25-MinuteTe131g

Abstract

The decay of 25-min ${\mathrm{Te}}^{131g}$ produced by ${\mathrm{Te}}^{130}(n,\gamma )$ has been investigated with the use of Ge(Li) and NaI(Tl) $\gamma$-ray detectors. Coincidence relationships among the $\gamma$ rays were determined in $\gamma -\gamma$ and sum-peak coincidence experiments. Because of the good resolution of the Ge(Li) detector we have been able to resolve complex $\gamma$-ray peaks observed in the ∼350- and 950- to 1000-keV regions in previous studies and to observe additional $\gamma$ rays. The energies (in keV) of observed $\gamma$ rays and their percentage intensities relative to 150-keV (in parentheses) are: 279 (1), 343 (1.1), 384 (1.1), 453 (24.0), 493 (7.0), 544 (0.4), 603 (5.9), 654 (1.8), 695 (0.5), 727 (0.4), 842 (0.2), 898 (0.3), 933 (1.2), 948 (3.0), 952 (0.6), 997 (5.1), 1007 (1.5), 1098 (0.8), 1147 (9.4), 1295 (1.4). The main changes from previous level schemes for ${\mathrm{I}}^{131}$ are the lowering of the ∼350-keV transitions to near the ground state and the addition of levels at 877, 1188, and 1445 keV. Preliminary measurements on the $\gamma$ rays of 1.2-day ${\mathrm{Te}}^{131m}$ are reported. Trends of the low-lying levels of odd-$A$ iodine isotopes from mass 127 to mass 131 are discussed. The half life of ${\mathrm{Te}}^{131g}$ was determined to be 25.0±0.1 min.