Characterization of SABRE crystal NaI-33 with direct underground counting

Abstract

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 ${}^{39}$K contamination of 4.3$\pm$0.2 ppb as determined by mass spectrometry. We measured a light yield of 11.1$\pm$0.2 photoelectrons/keV and an energy resolution of 13.2% (FWHM/E) at 59.5 keV. We evaluated the activities of ${}^{226}$Ra and ${}^{228}$Th inside the crystal to be $5.9\pm 0.6\mu$Bq/kg and $1.6\pm 0.3\mu$Bq/kg, respectively, which would indicate a contamination from ${}^{238}$U and ${}^{232}$Th at part-per-trillion level. We measured an activity of 0.51$\pm$0.02 mBq/kg due to ${}^{210}$Pb out of equilibrium and a $\alpha$ quenching factor of 0.63$\pm$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 $\sim$1 count/day/kg/keV in the [5-20] keV region.

References in corpus (8)

• The DAMA/LIBRA apparatus
• Low-Mass Dark Matter Search with CDMSlite
• First results on dark matter annual modulation from ANAIS-112 experiment
• An experiment to search for dark matter interactions using sodium iodide detectors
• Studies of Boosted Decision Trees for MiniBooNE Particle Identification
• Search for Electronic Recoil Event Rate Modulation with 4 Years of XENON100 Data
• Growth of Ultra-high Purity NaI(Tl) Crystal for Dark Matter Searches
• COSINE-100 and DAMA/LIBRA-phase2 in WIMP effective models

Cited by in corpus (12)

• Exploring coherent elastic neutrino-nucleus scattering using reactor electron antineutrinos in the NEON experiment
• High sensitivity characterization of an ultra-high purity NaI(Tl) crystal scintillator with the SABRE proof-of-principle detector
• Simulation and background characterisation of the SABRE South experiment
• Performance of the SABRE detector module in a purely passive shielding
• Upgrading the COSINE-100 Experiment for Enhanced Sensitivity to Low-Mass Dark Matter Detection
• Waveform Simulation for Scintillation Characteristics of NaI(Tl) Crystal
• The SABRE South Technical Design Report Executive Summary
• Cosmogenic activation of sodium iodide
• Progress in End-to-End Optimization of Detectors for Fundamental Physics with Differentiable Programming
• The role of small scale experiments in the direct detection of dark matter
• Pulse Shape Discrimination of low-energy nuclear and electron recoils for improved particle identification in NaI:Tl
• Characterisation of Hamamatsu R11065-20 PMTs for use in the SABRE South NaI(Tl) Crystal Detectors