Characterization of SABRE crystal NaI-33 with direct underground counting

Understand

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.