Development of low-background Cs

In this work, we present the first complex study of Cs$$_2$$ZrCl$$_6$$ (CZC) scintillating crystals in terms of their chemical purity, crystal radiopurity, scintillating performance and pulse-shape discrimination ability. An ICP-MS measurement exhibits a high purity of the CZC material (overall impurity level less than 10 $$\mu $$g/g). The CZC crystals show a very low content of radionuclides from U/Th natural decay chains. For $$^{40}$$K and $$^{137}$$Cs only limits at the level few mBq/kg were set after more than 650 h of measurement with a high purity germanium (HPGe) detector. Nevertheless, they contained cosmogenic $$^{134}$$Cs with an activity of about 50 mBq/kg. The measurements with two CZC crystals (11 and 24 g) as scintillating detectors over 456.5 d in the low-background DAMA/CRYS facility, deep underground at LNGS, supported a substantial radiopurity of these crystals leading to a counting rate of 0.17$$_{-0.11}^{+0.13}$$ (kg$$\cdot $$keV$$\cdot $$yr)$$^{-1}$$ at the $$Q_{2\beta }$$ of $$^{96}$$Zr (3.35 MeV). These detectors show a high particle-discrimination ability for $$\beta (\gamma )$$ and $$\alpha $$ particles. Limits on the half-lives of the double beta decays (DBD) of $$^{96}$$Zr and of $$^{94}$$Zr with and without neutrinos emission were also set at the level $$T_{1/2} \sim 10^{17}$$–$$10^{20}$$ yr (90$$\%$$ C.L.). The detailed analyses of the internal background components will also be useful for further developments of Cs$$_2$$ZrCl$$_6$$ low-background scintillating detectors and for the optimization of the experimental conditions