Improvement of radiopurity level of enriched 116^{116}CdWO4_4 and ZnWO4_4 crystal scintillators by recrystallization

As low as possible radioactive contamination of a detector plays a crucial role to improve sensitivity of a double beta decay experiment. The radioactive contamination of a sample of $^{116}$CdWO$_4$ crystal scintillator by thorium was reduced by a factor $\approx 10$, down to the level 0.01 mBq/kg ($^{228}$Th), by exploiting the recrystallization procedure. The total alpha activity of uranium and thorium daughters was reduced by a factor $\approx 3$, down to 1.6 mBq/kg. No change in the specific activity (the total $\alpha$ activity and $^{228}$Th) was observed in a sample of ZnWO$_4$ crystal produced by recrystallization after removing $\approx 0.4$ mm surface layer of the crystal.Comment: 14 pages, 5 figures and 2 table

Purification of molybdenum oxide, growth and characterization of medium size zinc molybdate crystals for the LUMINEU program

The LUMINEU program aims at performing a pilot experiment on neutrinoless double beta decay of 100Mo using radiopure ZnMoO4 crystals operated as scintillating bolometers. Growth of high quality radiopure crystals is a complex task, since there are no commercially available molybdenum compounds with the required levels of purity and radioactive contamination. This paper discusses approaches to purify molybdenum and synthesize compound for high quality radiopure ZnMoO4 crystal growth. A combination of a double sublimation (with addition of zinc molybdate) with subsequent recrystallization in aqueous solutions (using zinc molybdate as a collector) was used. Zinc molybdate crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski technique, their optical, luminescent, diamagnetic, thermal and bolometric properties were tested.Comment: Contribution to Proc. of Int. Workshop on Radiopure Scintillators RPSCINT 2013, 17-20 September 2013, Kyiv, Ukraine; to be published in EPJ Web of Conferences; expected to be online in January 2014; 6 pages, 6 figures, and 3 table

Scintillating bolometers based on ZnMoO4 and Zn100MoO4 crystals to search for 0ν2β decay of 100Mo (LUMINEU project): first tests at the Modane Underground Laboratory

The technology of scintillating bolometers based on zinc molybdate (ZnMoO4) crystals is under development within the LUMINEU project to search for decay of 100Mo with the goal to set the basis for large scale experiments capable to explore the inverted hierarchy region of the neutrino mass pattern. Advanced ZnMoO4 crystal scintillators with mass of ∼0.3 kg were developed and Zn100MoO4 crystal from enriched 100Mo was produced for the first time by using the low-thermal-gradient Czochralski technique. One ZnMoO4 scintillator and two samples (59 g and 63 g) cut from the enriched boule were tested aboveground at milli-Kelvin temperature as scintillating bolometers showing a high detection performance. The first results of the low background measurements with three ZnMoO4 and two enriched detectors installed in the EDELWEISS set-up at the Modane Underground Laboratory (France) are presented

Low thermal gradient Czochralski growth of large MWO4 (M = Zn, Cd) crystals, and microstructural and electronic properties of the (010) cleaved surfaces

The large optical-quality MWO4 (M = Zn, Cd) crystals of mass up to 14 (ZnWO4) and 20 (CdWO4) kg were grown by Low Thermal Gradient Czochralski Technique (LTG Cz). Crystallographic properties of MWO4(010) cleaved surface were evaluated by AFM and RHEED, and electronic structure of the surface was studied using XPS. A system of Kikuchi lines has been observed for cleaved MWO4(010) by RHEED confirming high crystallographic quality of the surface. The XPS valence-band and core-level spectra of MWO4(010) have been measured. The XPS measurements reveal that W and M atoms are in the formal valences 6+ and 2+, respectively, on cleaved MWO4(010) surface

Low thermal gradient Czochralski growth of large MWO4 (M = Zn, Cd) crystals, and microstructural and electronic properties of the (010) cleaved surfaces

The large optical-quality MWO4 (M = Zn, Cd) crystals of mass up to 14 (ZnWO4) and 20 (CdWO4) kg were grown by Low Thermal Gradient Czochralski Technique (LTG Cz). Crystallographic properties of MWO4(010) cleaved surface were evaluated by AFM and RHEED, and electronic structure of the surface was studied using XPS. A system of Kikuchi lines has been observed for cleaved MWO4(010) by RHEED confirming high crystallographic quality of the surface. The XPS valence-band and core-level spectra of MWO4(010) have been measured. The XPS measurements reveal that W and M atoms are in the formal valences 6+ and 2+, respectively, on cleaved MWO4(010) surface

Production and characterisation of a

We operated a $$\hbox {PbMoO}_4$$ scintillating cryogenic detector of 570 g, produced with archaeological lead. This compound features excellent low temperature characteristics in terms of light yield, 12 keV/MeV for $$\beta /\gamma$$ interactions, and FWHM energy resolution, 11.7 keV at 2.6 MeV. Furthermore, the detector allows for an effective particle identification by means of pulse shape analysis on the heat read-out channel. The implementation of innovative techniques and procedures for the purification of raw materials used for the crystal growth, and the highly-pure archaeological Pb, allowed for the production of large volume high-quality crystal. The overall characteristics of the detector operated at cryogenic temperatures makes $$\hbox {PbMoO}_4$$ an excellent compound for neutrino physics applications, especially neutrinoless double-beta studies

Development of ZnWO4 crystal scintillators for rare events search

The ZnWO4 crystal scintillator is a promising detector for low counting experiments thanks to the high level of radiopurity and reasonably high optical and scintillation properties. In particular, ZnWO4 scintillators can be utilized in the searches for double beta processes, in the investigation of rare alpha decays and Dark Matter. In fact, one of its main characteristics is to be an anisotropic detector. In the case of interaction of heavy particles or nuclear recoils, the light output and the time profile of the scintillation pulse depend on the direction of the particles with respect to the crystal axes; no difference is observed for γ/β radiation. These anisotropic features can offer a unique possibility to exploit the so-called directionality approach in order to investigate the presence of the Dark Matter candidates which induces nuclear recoils. In fact, their use can overcome the difficulty of detecting extremely short nuclear recoil traces

Effect of tungsten doping on ZnMoO4 scintillating bolometer performance

The introduction of a small quantity of tungsten oxide (in the range 0.2–0.5 wt%) into the melt improves the growth of ZnMoO4 crystals. No significant difference in the kinetics of scintillation decay, scintillation efficiency, emission spectra, optical transmittance was observed for three ZnMoO4 crystal samples grown from the melt of stoichiometric composition, with excess of molybdenum and doped with tungsten. Using CaWO4 as reference, the absolute light yield of ZnMoO4 is found to be equal to 3550±5503550±550 ph/MeV at 77 K. For two ZnMoO4 samples 20 mm in diameter and 40 mm in length (grown from the melt of stoichiometric composition and doped with tungsten) it is confirmed that scintillation and bolometric response are similar at milli-Kelvin temperature