Search for 2β processes in Zinc and Tungsten with ZnWO4 crystal scintillators

2011 - Search for 2β processes in 64Zn 70Zn, 180W, and 186W by using large volume (0.1 - 0.7 kg) low background ZnWO4 crystal scintillators has been performed. In particular

Four ZnWO4 crystal scintillators were used. Two crystals (117 g, 20 19 40 mm, and 699 g, 44 55 mm) were produced by the Czochralski method in the Institute for Scintillation Materials (Kharkiv, Ukraine). After 2130 h of low-background measurements, the crystal of 699 g was re-crystallized with the aim to study the effect of the re-crystallization on the radioactive contamination of the material. The third ZnWO4 crystal (141 g, 27 33 mm) was obtained by the recrystallization process and used in further measurements. The fourth ZnWO4 crystal scintillator (239 g, 41 27 mm) was produced in the Nikolaev Institute of Inorganic Chemistry (Novosibirsk, Russia) by the low-thermal gradient Czochralski technique. The radioactive contaminations of the used crystals have been measured.

The ZnWO4 crystal scintillators were fixed inside a cavity of 49 59 mm in the central part of a cylindrical polystyrene light-guide of 66 312 mm. The cavity was filled up with high purity silicone oil. The light-guide was optically connected on opposite sides by two low radioactivity PMTs. The detector was modified at the final stages of the experiment: two polished quartz light-guides (66 100 mm) were installed between the polystyrene light-guide and the PMTs to suppress gamma ray background from the PMTs. The detector has been installed in the low background DAMA/R&D set-up.