Study of $\boldsymbol{\beta}$ Decay Shape Factors in First-Forbidden Transitions with $\boldsymbol{\Delta I^\pi = 0^-}$ for Reactor Antineutrino Spectra Predictions

TL;DR

This study measures the beta decay spectra of key isotopes contributing to reactor antineutrino flux, comparing experimental data with theoretical models to improve spectral predictions.

Contribution

It provides new experimental beta spectra for $^{92}$Rb and $^{142}$Cs and evaluates shape models for first-forbidden transitions, enhancing reactor antineutrino spectrum accuracy.

Findings

Measured beta spectra match models using absorption spectroscopy feedings

First-forbidden transition shape factors are consistent with experimental data

Results improve predictions of reactor antineutrino spectra

Abstract

The electron spectra of the $\beta$ decays of $^{92}$Rb and $^{142}$Cs, key contributors to the reactor antineutrino spectrum, were measured at the IGISOL facility using radioactive beams of high isotopic purity. The shapes of the measured $\beta$ spectra were compared with various $\beta$ shape models, including first-forbidden correction factors for $\Delta I^\pi = 0^-$ ground-state to ground-state transitions. Comparisons with previous experimental results are also provided. The shapes of the newly measured $\beta$ spectra are well reproduced employing feedings extracted from total absorption gamma spectroscopy measurements.