Nonproportionality of NaI(Tl) scintillation detector for dark matter search experiments
Seung Mok Lee, Prabal Adhikari, N. Carlin, Jin Cho, J. J. Choi, S. Choi, A. C. Ezeribe, L. E. França, C. Ha, I. S. Hahn, Sophia J. Hollick, E. J. Jeon, H. W. Joo, W. G. Kang, M. Kauer, B. H. Kim, H. J. Kim, J. Kim, K.W. Kim, S. H. Kim, S. K. Kim, S. W. Kim, W. K. Kim, Y.D. Kim, Y. H. Kim, Y. J. Ko, D. H. Lee, E. K. Lee, H. Lee, H. S. Lee, H. Y. Lee, I.S. Lee, J. Lee, Ji Yeoun Lee, M. H. Lee, S. H. Lee, Y. J. Lee, D. S. Leonard, N. T. Luan, B. B. Manzato, R. Maruyama, R. J. Neal, J. A. Nikkel, S. L. Olsen, B. J. Park, H. K. Park, H. S. Park, Jong-Chul Park, K. S. Park, S. D. Park, R. L. C. Pitta, H. Prihtiadi, S. J., C. Rott, K. A. Shin, D. F. F. S. Cavalcante, A. Scarff, Myungwoo Son, N.J.C. Spooner, L. T. Truc, L. Yang, G. H. Yu
Abstract
Abstract 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 $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> spectroscopy, measures light yields across diverse energy levels from full-energy $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> peaks produced by the decays of various isotopes. These $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> 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 $$\mathrm {^{22}Na}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>22</mml:mn> </mml:msup> <mml:mi>Na</mml:mi> </mml:mrow> </mml:math> 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.