Search for double beta decay of zinc and tungsten with low background ZnWO4 crystal scintillators

Abstract

Double beta processes in 64 Zn, 70 Zn, 180 W, and 186 W have been searched for with the help of large volume (0.1 − 0.7 kg) low background ZnWO 4 crystal scintillators at the Gran Sasso National Laboratories of the INFN. Total time of measurements exceeds 10 thousands hours. New improved half-life limits on double electron capture and electron capture with positron emission in 64 Zn have been set, in particular (all the limits are at 90% C.L.): T 0ν2ε 1/2 ≥ 1.1 × 10 20 yr, T 2νεβ +

Radiopurity of ZnWO4Crystal Scintillators

“…2. The peak in the spectrum at the energy 1131 ± 8 keV cannot be explained by contribution from external γ rays 5 . We suppose presence of 65 Zn 6 (T 1/2 = 244.26 d, Q β = 1351.9 keV [18]) in the crystal to explain the peak.…”

“…A few peaks in the spectra can be ascribed to γ quanta of naturally occurring radionuclides 40 K, 214 Bi ( 238 U chain) and 208 Tl ( 232 Th) from materials of the setup. The data of the run 2 and run 3 have already been analyzed and published in [5]. …”

“…in order to study its radioactive contamination, and to search for double beta decay of zinc and tungsten isotopes [2]. Recently, radiopurity of large volume ZnWO 4 scintillator (mass of 119 g) has also been tested in the SUL [3]; other detectors (with masses of 0.1-0.7 kg) have been measured at Laboratori Nazionali del Gran Sasso (LNGS) [4,5]. Possibilities to apply ZnWO 4 crystals for dark matter search were discussed in Ref.…”

ZnWO4anisotropic scintillator for Dark Matter investigation with the directionality technique

“…More recently, radiopurity and double beta decay processes of zinc and tungsten have been further studied also at LNGS using new developed ZnWO 4 detectors with masses 0.1 − 0.7 kg [8,9,18,19]. The growth of the crystals, the scintillation properties, the pulse shape discrimination capability, the anisotropic properties, the residual radioactive contamination and the possible applications have been deeply studied [8,10,14,15,[17][18][19][20]. The obtained results are very promising and an R&D to produce ZnWO 4 crystals having higher radiopurity is still ongoing.…”

Search for rare processes with ZnWO4crystal scintillators

“…In recent years ZnWO 4 crystal scintillators were considered in the search for rare processes [1][2][3][4][5]. In particular four clear, slightly colored ZnWO 4 crystal scintillators have been produced: i) crystals ZWO-1 (117 g) and ZWO-2 (699 g) were produced in the Institute for Scintillation Materials (ISMA, Kharkiv, Ukraine) from crystal ingots grown in platinum crucibles by the Czochralski method; ii) the crystal ZWO-3 (141 g) was obtained by recrystallization from the sample ZWO-2 at the ISMA; iii) the ZWO-4 (239 g) was produced in the Nikolaev Institute of Inorganic Chemistry (Novosibirsk, Russia) by the low-thermal gradient Czochralski technique also in platinum crucible.…”