Journal Article

Characterization of SABRE crystal NaI-33 with direct underground counting

Benziger, J, Wallner, A, Bignell, L J, Stuchbery, A E, Pietrofaccia, L, Scutti, F, Baroncelli, T, Vignoli, C, D’Imperio G, Krishnan, S, Tomei, C, Bolognino, I, Antonello, M, Diemoz, M, Lane, G J, Nuti, F, D’Angelo D, D’Incecco M, Dix, W, Ianni, A, Souza, M, Arnquist, I J, Suerfu, B, Rahatlou, S, Mould, J, Iannone, M, Barberio, E, Urquijo, P, Wada, M, Mariani, A, Duffy, A R, Dafinei, I, Milana, S, Hoppe, E, Di, Carlo G, Zurowski, M, Mahmood, I, Orlandi, D, Ioannucci, L, Pettinacci, V, Calaprice, F, Di, Ludovico A, Williams, A G, Di, Giacinto A, Zani, A, Copello, S

2021

Overview

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 39K 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 226Ra and 228Th inside the crystal to be 5.9±0.6μBq/kg and 1.6±0.3μBq/kg, respectively, which would indicate a contamination from 238U and 232Th at part-per-trillion level. We measured an activity of 0.51 ± 0.02 mBq/kg due to 210Pb out of equilibrium and a α 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.

• Publisher: Springer Nature B.V
• Subject: Astrophysics / Contamination / Crystals / Dark matter / Energy / Energy resolution / Energy spectra / Experiments / Laboratories / Lead isotopes / Mass spectrometry / Photoelectrons / Radioactivity / Radium 226 / Shielding