https://doi.org/10.1140/epjc/s10052-021-09473-2
Regular Article - Experimental Physics
Identification of new isomers in 
Ac: impact on dark matter searches
1
Center for Underground Physics, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
2
Department of Physics, University of California, San Diego, 92093, La Jolla, CA, USA
3
Department of Physics and Wright Laboratory, Yale University, 06520, New Haven, CT, USA
4
Physics Institute, University of São Paulo, 05508-090, São Paulo, Brazil
5
Department of Physics and Astronomy, Seoul National University, 08826, Seoul, Republic of Korea
6
Department of Physics, Bandung Institute of Technology, 40132, Bandung, Indonesia
7
Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
8
Department of Physics, Chung-Ang University, 06973, Seoul, Republic of Korea
9
Department of Science Education, Ewha Womans University, 03760, Seoul, Republic of Korea
10
Center for Exotic Nuclear Studies, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
11
IBS School, University of Science and Technology (UST), 34113, Daejeon, Republic of Korea
12
Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, 53706, Madison, WI, USA
13
Department of Physics, Kyungpook National University, 41566, Daegu, Republic of Korea
14
Department of Physics and Astronomy, Sejong University, 05006, Seoul, Republic of Korea
15
Korea Research Institute of Standards and Science, 34113, Daejeon, Republic of Korea
16
Department of Accelerator Science, Korea University, 30019, Sejong, Republic of Korea
17
Department of Physics, Sungkyunkwan University, 16419, Seoul, Republic of Korea
ac
hyunsulee@ibs.re.kr
bg
hyunsulee@ibs.re.kr
Received:
10
May
2021
Accepted:
13
July
2021
Published online:
18
August
2021
We report the identification of metastable isomeric states of 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 
-decay of Ra, a component of the 
Th decay chain, with Q-values of 39.52 keV, 39.13 keV and 25.61 keV, respectively. Due to the low Q-value of Ra as well as the relative abundance of Th and their progeny in low background experiments, these observations potentially impact the low-energy background modeling of dark matter search experiments.
© The Author(s) 2021
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