Measurement of ^136gsI and ^136mI β-decay properties with MTAS

Since most fission products in a nuclear reactor undergo beta decay to reach stability, understanding the beta feeding and gamma-ray intensities of these beta-decaying fission products is essential. This knowledge is important for simulating reactor decay heat and is, therefore, crucial for ensuring reactor safety. Most of the data available is based on high-resolution spectroscopy, which in general attributes too little decay energy to the gamma rays and too much to beta particles and antineutrinos, affecting the anti-neutrino flux calculations as well. Measurements using a high-efficiency (though lower resolution) detector such as the MTAS (Modular Total Absorption Spectrometer) can correct this bias in the decay data. We present results from a study of beta-feeding intensities for the ¹³⁶I ground state and isomeric state using data collected with MTAS at the Holifield Radioactive Ion Beam Facility at ORNL (Oak Ridge National Laboratory). Half-lives and gamma-ray energies are used to discriminate between the ground and isomeric states. The separated spectra are then used to extract the beta-feeding intensities for both initial states of ¹³⁶I. Preliminary results will be presented.