https://doi.org/10.1140/epjc/s10052-026-15738-5
Regular Article - Experimental Physics
Quenching factors for Na recoils as a function of Tl dopant concentrations in NaI(Tl) crystals
1
Max-Planck-Institut für Physik, 85748, Garching, Germany
2
Institut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften, 1050, Wien, Austria
3
Atominstitut, Technische Universität Wien, 1020, Wien, Austria
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CNR-SPIN c/o Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell’Aquila, 67100, L’Aquila, Italy
5
Consiglio Nazionale delle Ricerche, Istituto di Nanotecnologia, 00185, Rome, Italy
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Department of Mathematics and Physics, North Carolina Central University, 27707, Durham, NC, USA
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Department of Nuclear Engineering, North Carolina State University, 27695, Durham, NC, USA
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Department of Physics, Duke University, 27708, Durham, NC, USA
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Department of Physics, ETH Zurich, 8093, Zurich, Switzerland
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Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell’Aquila, 67100, L’Aquila, Italy
11
ETH Zurich - PSI Quantum Computing Hub, Paul Scherrer Institute, 5232, Villigen, Switzerland
12
Gran Sasso Science Institute, 67100, L’Aquila, Italy
13
Helsinki Institute of Physics, University of Helsinki, 00014, Helsinki, Finland
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INFN - Laboratori Nazionali del Gran Sasso, 67010, Assergi, Italy
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INFN - Sezione di Roma, 00185, Rome, Italy
16
SNOLAB, P3Y 1N2, Lively, Canada
17
State Key Laboratory of Functional Crystals and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 201899, Shanghai, People’s Republic of China
18
Triangle Universities Nuclear Laboratory, 27708, Durham, NC, USA
a
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Received:
24
July
2025
Accepted:
21
April
2026
Published online:
6
May
2026
Abstract
Thallium-doped sodium iodide (NaI(Tl)) scintillation detectors play an important role in the field of direct dark matter (DM) searches. The DAMA/LIBRA experiment stands out for its reported observation of an annually modulating DM-like signal, which is in direct contrast with other results. To accurately calibrate the energies of nuclear recoil signals with electron recoils, precise measurements of the quenching factor of the NaI(Tl) crystals are essential, as the two processes have different scintillation light yield. In this article, we present results of a systematic study carried out by the COSINUS collaboration and Duke University to measure the quenching factor of sodium (Na) recoils as a function of nuclear recoil energy and for differing Thallium (Tl) dopant concentrations in the bulk crystal. Five ultrapure NaI(Tl) crystals, manufactured by the Shanghai Institute for Ceramics, were irradiated with a quasi-monoenergetic neutron beam at the Triangle Universities Nuclear Laboratory, North Carolina, USA. The quenching factor for nuclear recoils off Na with low energies of 6–26keV
was extracted for all crystals, using two proportional calibration schemas with lines from a 
Am source and a 
Ba source. A Tl-dependence could be deduced in both cases, where a lower Tl concentration leads to smaller observed QF.
© The Author(s) 2026
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Funded by SCOAP3.
