Low-Energy Beta-Ray Transition in the Decay ofI128

The gamma-ray spectrum of ${\mathrm{I}}^{128}$ was investigated with a scintillation well counter and auxiliary coincidence apparatus to search for a beta-ray transition to a high-energy ${\mathrm{Xe}}^{128}$ level. A transition to an excited state at 1570±30 keV in ${\mathrm{Xe}}^{128}$ was observed to take place with a probability of (6±3)×${10}^{-3\mathrm{}}$%. The deexcitation of this state takes place primarily by way of the first excited state, the probability of gamma-ray decay directly to the ground state being less than 10%. The energy of the second excited state is found to be 975±15 keV.