Radioactive contamination of ZnW0_4 crystal scintillators

摘要

The radioactive contamination of ZnW0_4 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 h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnW0_4 samples. One of the ZnW0_4 crystals has also been tested by ultra-low background γ spectrometry. The radioactive contaminations of the best ZnW0_4 samples are estimated to be less than 0.002 mBq/kg (228Th and ~226Ra), the total a activity is 0.18 mBq/kg. The β active~ 65Zn and the α active ~180W have been detected in ZnW0_4 crystals. The effect of the re-crystallization on the radiopurity of the ZnW0_4 crystal has been studied. The radioactive contamination of the ceramic components of the set-ups used in the crystals growth has been checked by low background y spectrometry. Some ideas for future improvement of the radiopurity level of ZnWO_4 crystal scintillators are briefly discussed.