Radioactive contamination of ZnWO4 crystal scintillators

TL;DR

This study measures the radioactive contamination levels in ZnWO4 crystal scintillators using underground detection and simulations, identifying specific radionuclides and effects of re-crystallization to improve radiopurity.

Contribution

It provides detailed contamination measurements and analysis of factors affecting radiopurity in ZnWO4 crystals, with a focus on improving scintillator quality.

Findings

Radioactive contamination levels do not exceed 0.8 mBq/kg.

Detected specific radionuclides 65Zn and 180W.

Re-crystallization impacts radiopurity.

Abstract

The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed.