Radiopurity of ZnWO₄Crystal Scintillators

Abstract

Recently ZnWO4 was proposed as perspective material for low-counting experiments to search for rare processes. Such experiments demand high radiopurity of ZnWO4 crystal scintillators. With this aim radioactive contamination of large volume (0.1-0.7 kg) ZnWO4 crystal scintillators were measured in the underground Laboratori Nazionali del Gran Sasso of the INFN at the depth of ≈ 3600 m water equivalent.

Radioactive contamination of ZnWO4 crystal scintillators

“…The radioactive contamination of a 119 g ZnWO 4 scintillator was measured to be on the mBq/kg level in the Solotvina Underground Laboratory [16,9]. Long-time low background scintillation measurements using several ZnWO 4 crystal scintillators (with mass in the range 0.1 − 0.7 kg) have been performed at the LNGS with the aim to search for double β processes in zinc and tungsten isotopes [17,18,19]. The data collected with different ZnWO 4 crystals in the same set-up also allow the estimation of the level of the radioactive contamination of the material.…”

Status and Perspectives of 2ϵ, ϵβ+ and 2β+ Decays

“…Moreover, low background crystal scintillators are being used for a long time in rare α and β decays (see e.g., [78]). Hoverer, a very wide choice of scintillators is available for DBD experiments, such as CdWO 4 (due to 106 Cd, 108 Cd, 114 Cd, 116 Cd, 180 W, 186 W), CaMoO 4 (due to 100 Mo), and their enrichments (such as 106 Cd, 116 Cd and 100 Mo) [31,[79][80][81][82][83][84] [51][52][53]58,[91][92][93][94][95][96][97][98][99][100][101][102][103][104]. Moreover, as other example, rare-earth-doped scintillators (CaF 2 (Eu), LaCl 3 (Ce), etc.)…”

“…or scintillators, such as CdWO 4 and CaWO 4 , are used to study very specific nuclear rare processes [105][106][107][108]. Extensive literature on historical benchmarks and the industrial production of crystals is available, see, e.g., [51,52,58,[85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119].…”

Epitaxial growth of ZnO nanocrystals at ZnWO4(010) cleaved surface

“…Zinc tungstate, ZnWO 4 , related to family of wolframite-type crystals with general composition A 2+ WO 4 is one from the best known scintillating media [1,2]. Potentials of this material for laser techniques, acoustics and photocatalytic technologies are under considerations [3][4][5][6].…”

“…The ZnWO 4 crystals are characterized by good cleavage properties of (0 1 0) planes. Presently large high-quality ZnWO 4 single crystals grown in the [0 1 0] direction are available [2,[7][8][9] and these crystals can be used for fabrication of optical devices and substrates with surfaces prepared by cleavage.…”