https://doi.org/10.1140/epjc/s10052-024-12770-1
Regular Article - Experimental Physics
Nonproportionality of NaI(Tl) scintillation detector for dark matter search experiments
1
Department of Physics and Astronomy, Seoul National University, 08826, Seoul, Republic of Korea
2
Department of Physics and Wright Laboratory, Yale University, 06520, New Haven, CT, USA
3
Physics Institute, University of São Paulo, 05508-090, São Paulo, Brazil
4
Center for Underground Physics, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
5
Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
6
Department of Physics, Chung-Ang University, 06973, Seoul, Republic of Korea
7
Center for Exotic Nuclear Studies, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
8
Department of Science Education, Ewha Womans University, 03760, Seoul, Republic of Korea
9
IBS School, University of Science and Technology (UST), 34113, Daejeon, Republic of Korea
10
Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, 53706, Madison, WI, USA
11
Department of Physics, Kyungpook National University, 41566, Daegu, Republic of Korea
12
Department of Physics, Sejong University, 05006, Seoul, Republic of Korea
13
Korea Research Institute of Standards and Science, 34113, Daejeon, Republic of Korea
14
Department of Accelerator Science, Korea University, 30019, Sejong, Republic of Korea
15
Department of Physics and IQS, Chungnam National University, 34134, Daejeon, Republic of Korea
16
Department of Physics, Universitas Negeri Malang, 65145, Malang, Indonesia
17
Department of Physics, Sungkyunkwan University, 16419, Suwon, Republic of Korea
18
Department of Physics and Astronomy, University of Utah, 84112, Salt Lake City, UT, USA
Received:
17
January
2024
Accepted:
8
April
2024
Published online:
9
May
2024
We present a comprehensive study of the nonproportionality of NaI(Tl) scintillation detectors within the context of dark matter search experiments. Our investigation, which integrates COSINE-100 data with supplementary 
spectroscopy, measures light yields across diverse energy levels from full-energy peaks produced by the decays of various isotopes. These peaks of interest were produced by decays supported by both long and short-lived isotopes. Analyzing peaks from decays supported only by short-lived isotopes presented a unique challenge due to their limited statistics and overlapping energies, which was overcome by long-term data collection and a time-dependent analysis. A key achievement is the direct measurement of the 0.87 keV light yield, resulting from the cascade following electron capture decay of 
from internal contamination. This measurement, previously accessible only indirectly, deepens our understanding of NaI(Tl) scintillator behavior in the region of interest for dark matter searches. This study holds substantial implications for background modeling and the interpretation of dark matter signals in NaI(Tl) experiments.
© The Author(s) 2024
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Funded by SCOAP3.
