High sensitivity characterization of an ultrahigh purity NaI(Tl) crystal scintillator with the SABRE proof-of-principle detector

Calaprice, F.; Copello, S.; Dafinei, I.; D’Angelo, D.; D'imperio, Giulia; Carlo, G. Di; Diemoz, M.; Giacinto, A. Di; Lüdovico, A. Di; Ianni, A.; Iannone, M.; Marchegiani, Francesca; Mariani, Alberto; Milana, Silvia; Nisi, S.; Nuti, F.; Orlandi, D.; Pettinacci, V.; Pietrofaccia, L.; Rahatlou, S.; Souza, Michael J.; Suerfu, B.; Tomei, C.; Vignoli, C.; Wada, M.; Zani, A.

doi:10.1103/physrevd.104.l021302

Cited by 15 publications

(23 citation statements)

References 35 publications

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“…This background level is comparable to that measured within the PoP setup, i.e. 1.20 ± 0.05 cpd/kg/keV [2]. Such result demonstrates that, as the vetoable crystal internal contaminants (e.g.…”

Section: Resultssupporting

confidence: 80%

“…In addition, 210 Pb from the PTFE reflector wrapping the crystal was included to reproduce the peak at ∼12 keV due to X-rays from 210 Pb. All rates are allowed to vary freely with the following exceptions: 40 K rate has a penalty determined by the PoP-measured value (0.07±0.05 µBq/kg [2]); 226 Ra, 232 Th have penalties to the activities determined by measuring Bi-Po sequences in [7].…”

Section: Resultsmentioning

confidence: 99%

“…The energy of the event is then obtained dividing the total number of photoelectrons of the two PMTs by the photoelectron yield of the detector module. The photoelectron yield was measured in [2] and comprises the following unresolved effects: the light yield of the crystal, the light loss upon reflection on the crystal's PTFE reflector foil (side surfaces), the geometrical optical coverage and coupling, and the quantum efficiency of the PMTs.…”

Section: Data Processing and Calibrationmentioning

confidence: 99%

“…In [7] we have introduced a traditional cut-based analysis and a more innovative Boosted Decision Trees (BDT) [8] approach that exploits the above variables to obtain high acceptance of scintillation events while efficiently rejecting the noise with a specific focus on events up to 100 keV. In [2] we applied the simple cut-based selection, while in this work we chose to use the multivariate approach with BDT in order to maximize the signal acceptance at low energy. Decision trees are a popular method for classification tasks in supervised machine learning.…”

Section: Event Selectionmentioning

confidence: 99%

“…The key element in achieving this ambitious goal is the use of ultra-high purity NaI(Tl) crystal. In this pathway the crystal denominated NaI-33 was thoroughly characterized in 2020 inside the SABRE Proof-of-Principle (PoP) detector [2] at Laboratori Nazionali del Gran Sasso (LNGS). The PoP detector was equipped with a liquid scintillator veto in addition to a passive shielding to further reduce the background level in the ROI [3].…”

Section: Introductionmentioning

confidence: 99%

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Performance of a SABRE detector module without an external veto

Calaprice¹,

Benziger²,

Copello³

et al. 2022

Preprint

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We present here a characterization of the low background NaI(Tl) crystal NaI-33 based on a period of almost one year of data taking (891 kg×days exposure) in a detector configuration with no use of organic scintillator veto. This remarkably radio-pure crystal already showed a low background in the SABRE Proof-of-Principle (PoP) detector, in the low energy region of interest (1-6 keV) for the search of dark matter interaction via the annual modulation signature. As the vetoable background components, such as 40 K, are here sub-dominant, we reassembled the PoP setup with a fully passive shielding. We upgraded the selection of events based on a Boosted Decision Tree algorithm that rejects most of the PMT-induced noise while retaining scintillation signals with > 90% efficiency in 1-6 keV. We find an average background of 1.35 ± 0.02 cpd/kg/keV in the region of interest and a spectrum consistent with data previously acquired in the PoP setup, where the external veto background suppression was in place. Our background model indicates that the dominant background component is due to decays of 210 Pb, only partly residing in the crystal itself. The other location of 210 Pb is the reflector foil that wraps the crystal. We now proceed to design the experimental setup for the physics phase based on an array of similar crystals, using a low radioactivity PTFE reflector and further improving the passive shielding strategy compliant with the new safety and environmental requirements of Laboratori Nazionali del Gran Sasso.

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Data Processing and Calibrationmentioning

confidence: 99%

Section: Event Selectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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