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K. W. Kim; G. Adhikari; E. Barbosa de Souza; N. Carlin; J. J. Choi; S. Choi; M. Djamal; A. C. Ezeribe; L. E. França; C. Ha; I. S. Hahn; E. J. Jeon; J. H. Jo; W. G. Kang; M. Kauer; H. Kim; H. J. Kim; S. H. Kim; S. K. Kim; W. K. Kim; Y. D. Kim; Y. H. Kim; Y. J. Ko; E. K. Lee; H. Lee; H. S. Lee; H. Y. Lee; I. S. Lee; J. Lee; J. Y. Lee; M. H. Lee; S. H. Lee; S. M. Lee; D. S. Leonard; B. B. Manzato; R. H. Maruyama; R. J. Neal; S. L. Olsen; B. J. Park; H. K. Park; H. S. Park; K. S. Park; R. L. C. Pitta; H. Prihtiadi; S. J. Ra; C. Rott; K. A. Shin; A. Scarff; N. J. C. Spooner; W. G. Thompson; L. Yang; G. H. Yu; COSINE-100 Collaboration
The European physical journal. C, Particles and fields, 08/2021, Volume: 81, Issue: 8Journal Article
Abstract We report the identification of metastable isomeric states of $$^{228}$$ 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 $$\beta $$ β -decay of $$^{228}$$ 228 Ra, a component of the $$^{232}$$ 232 Th decay chain, with $$\beta $$ β Q-values of 39.52 keV, 39.13 keV and 25.61 keV, respectively. Due to the low Q-value of $$^{228}$$ 228 Ra as well as the relative abundance of $$^{232}$$ 232 Th and their progeny in low background experiments, these observations potentially impact the low-energy background modeling of dark matter search experiments.
