Identification of new isomers in ${}^{228}$Ac : Impact on dark matter searches

Abstract

We report the identification of metastable isomeric states of ${}^{228}$Ac at 6.28 keV, 6.67 keV and 20.19 keV, with lifetimes of an order of 100 ns. These states are produced by the $\beta$-decay of ${}^{228}$Ra, a component of the ${}^{232}$Th decay chain, with $\beta$ Q-values of 39.52 keV, 39.13 keV and 25.61 keV, respectively. Due to its low Q-value as well as the relative abundance of ${}^{232}$Th and their progeny in low background experiments, these observations potentially impact the low-energy background modeling of dark matter search experiments.

arXiv comment9 pages, 9 figures

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