Total Absorption Spectroscopy of the $^{137}$Xe, $^{137}$I, and $^{92}$Rb $\beta$-Decays*

The NaI(Tl) based Modular Total Absorption Spectrometer (MTAS) was constructed to measure improved $\beta$-decay feeding patterns from neutron-rich nuclei. It is difficult to measure $\beta$-decay feeding intensities with high precision $\gamma$-ray measurements due to the low efficiency of high precision detectors. There are several important applications of improved measurements of $\beta$-decay feeding patterns by total absorption spectroscopy; improve understanding of elemental abundances in the universe, help with stockpile stewardship, contribute to understanding of underlying nuclear structure, and improve $\beta$-decay feeding measurements to calculate accurately the $\bar{\nu}_e$ spectra needed to evaluate precisely reactor neutrino measurements. We present $\beta$-decay feeding results for two ``priority one" measurements, $^{137}$Xe and $^{137}$I, and for $^{92}$Rb, which is a large individual contributor to the $\bar{\nu}_e$ uncertainty of the reactor anomaly. In addition to $\beta$-$\gamma$ decays, $^{137}$I has a $\beta$-neutron decay channel which is measurable in MTAS. We will demonstrate techniques for analyzing MTAS $\gamma$-decay data. We will also describe $\beta$ and neutron spectroscopy in MTAS.