Decay of the 55 min and 12 min 133Te isomers

Abstract Gamma rays emitted in the decay of the 133 Te isomers, 55.4 min 133m Te and 12.5 min 133g Te, have been observed with Ge(Li) detectors. Sources were prepared by separating Sb from fission products, allowing several minutes for decay of 2.7 min 133 Sb and then separating the Te daughter activities. A total of 29 γ-rays between 312 and 2541 keV were attributed to decay of 133g Te and 30 from 74 to 2050 keV to that of 133m Te. Gamma-gamma coincidences in the decay of 133g Te were observed with a NaI(Tl) Ge(Li) set-up. The decay scheme of 133g Te was constructed, involving placement of 25 of the γ-rays emitted. The decay of 133g Te populates levels in 133 I at 0, 312, 720, 787, 1313, 1333, 1374, 1565, 1718, 2137, 2194 and 2541 keV. The decay of 133m Te is very complicated, and we have not attempted construction of a complete decay scheme for it; however, levels at 913 and 1561 keV in 133 I are definitely populated in 133m Te decay. The value for Q β of 133 Te was measured as 3.52±0.10 MeV. The low-lying levels of the odd-mass iodine isotopes vary smoothly through the series 125 I through 133 I. The levels of 133 I are fitted rather well by predictions based on quasi-particle-phonon coupling.