https://doi.org/10.1140/epjc/s10052-021-09098-5
Regular Article – Experimental Physics
Characterization of SABRE crystal NaI-33 with direct underground counting
1
INFN-Sezione di Milano, 20133, Milan, Italy
2
Pacific Northwest National Laboratory, 99352, Richland, WA, USA
3
School of Physics, The University of Melbourne, 3010, Melbourne, VIC, Australia
4
Chemical Engineering Department, Princeton University, 08544, Princeton, NJ, USA
5
Department of Nuclear Physics, The Australian National University, 2601, Canberra, ACT, Australia
6
Dipartimento di Fisica, Università degli Studi di Milano, 20133, Milan, Italy
7
Physics Department, Princeton University, 08544, Princeton, NJ, USA
8
Gran Sasso Science Institute, 67100, L’Aquila, Italy
9
INFN-Laboratori Nazionali del Gran Sasso, 67100, Assergi (L’Aquila), Italy
10
INFN-Sezione di Roma, 00185, Rome, Italy
11
ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO), Sydney, Australia
12
Centre for Astrophysics and Supercomputing, Swinburne University of Technology, 3122, Hawthorn, VIC, Australia
13
Dipartimento di Fisica, Sapienza Università di Roma, 00185, Rome, Italy
14
The University of Adelaide, 5005, Adelaide, SA, Australia
15
Dipartimento di Fisica, Università degli Studi di Genova and INFN Genova, 16146, Genoa, Italy
16
Department of Physics, University of California, Berkeley, 94720, Berkeley, CA, USA
17
Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences, 00-716, Warsaw, Poland
n
giulia.dimperio@roma1.infn.it
Received:
4
December
2020
Accepted:
27
March
2021
Published online:
9
April
2021
Ultra-pure NaI(Tl) crystals are the key element for a model-independent verification of the long standing DAMA result and a powerful means to search for the annual modulation signature of dark matter interactions. The SABRE collaboration has been developing cutting-edge techniques for the reduction of intrinsic backgrounds over several years. In this paper we report the first characterization of a 3.4 kg crystal, named NaI-33, performed in an underground passive shielding setup at LNGS. NaI-33 has a record low 
K contamination of 4.3 ± 0.2 ppb as determined by mass spectrometry. We measured a light yield of 11.1 ± 0.2 photoelectrons/keV and an energy resolution of 13.2% (FWHM/E) at 59.5 keV. We evaluated the activities of 
Ra and 
Th inside the crystal to be 
Bq/kg and 
Bq/kg, respectively, which would indicate a contamination from 
U and 
Th at part-per-trillion level. We measured an activity of 0.51 ± 0.02 mBq/kg due to 
Pb out of equilibrium and a 
quenching factor of 0.63 ± 0.01 at 5304 keV. We illustrate the analyses techniques developed to reject electronic noise in the lower part of the energy spectrum. A cut-based strategy and a multivariate approach indicated a rate, attributed to the intrinsic radioactivity of the crystal, of 
1 count/day/kg/keV in the [5–20] keV region.
© The Author(s) 2021
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Funded by SCOAP3
