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.

9 pages, 9 figures

References in corpus (6)

• A direct empirical proof of the existence of dark matter
• An experiment to search for dark matter interactions using sodium iodide detectors
• Tests on NaI(Tl) crystals for WIMP search at the Yangyang Underground Laboratory
• Strong constraints from COSINE-100 on the DAMA dark matter results using the same sodium iodide target
• Performance of a prototype active veto system using liquid scintillator for a dark matter search experiment
• A facility for mass production of ultra-pure NaI powder for the COSINE-200 experiment