# Total Absorption Spectroscopy Study of the Beta Decay of $^{86}$Br and $^{91}$Rb

## TL;DR

This study used total absorption spectroscopy to accurately measure the beta decay of $^{86}$Br and $^{91}$Rb, revealing the Pandemonium effect and its implications for reactor decay heat and antineutrino predictions.

## Contribution

It provides new decay data for $^{86}$Br and $^{91}$Rb, correcting previous measurements affected by the Pandemonium effect, and evaluates their impact on reactor models.

## Key findings

- Both decays suffer from the Pandemonium effect.
- Previous measurements by Rudstam et al. need renormalization.
- The decays significantly influence reactor decay heat and antineutrino spectra.

## Abstract

The beta decays of $^{86}$Br and $^{91}$Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyv\"askyl\"a and further purified using the JYFLTRAP. $^{86}$Br and $^{91}$Rb are considered to be major contributors to the decay heat in reactors. In addition $^{91}$Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam {\it et al.} assuming that this decay was well known from high-resolution measurements. Our results show that both decays were suffering from the {\it Pandemonium} effect and that the results of Rudstam {\it et al.} should be renormalized. The relative impact of the studied decays in the prediction of the decay heat and antineutrino spectrum from reactors has been evaluated.