Search

A scintillating crystal that contains a candidate isotope for DBD provides a promising technique for the high detection-efficiency and good energy resolution. The AMoRE (Advanced Molybdenum based Rare process Experiment) collaboration is studying the potential of CaMoO4 scintillation crystals for searches for looMo 0v DBD.

Scintillation properties and radioactive contamination of calcium molybdate scintillating crystals depleted in 48Ca and enriched in 100Mo (40Ca100MoO4 ) have been studied to prepare a 100Mo-based neutrinoless double beta decay experiment. The prospects of a neutrinoless double beta decay experiment using 40Ca100MoO4 crystals are discussed.

The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed., Comment: 15 pages, 8 figures, 6 tables, submitted for publication

Search for neutrino-less double beta decay of 100Mo is proposed using active method with Ca 100MoO4 scintillation crystals which show the brightest scintillation light among variety of inorganic scintillation materials containing Mo. Study of X-ray luminescence and scintillation properties such as energy response, number of photoelectrons/keV, absolute light yield, decay time, pulse shape discrimination and radioactive contamination of CaMoO4 crystals grown by the Czochralski method with different conditions are presented. Further R&D of resolution optimization, crystal quality improvement and background reduction are underway. Significant improvement of sensitivity to neutrino-less double beta decay can be achieved by using 10 Mo enriched Ca 100MoO4 crystals with good energy resolution and low background. Further reduction of background induced by 48 Ca two neutrino double beta decay can be achieved by using 48Ca depletion. We are planning to install several kilograms of Ca 100MoO4 crystals depleted in 48Ca at underground laboratory for the neutrino-less double beta decay experiment in the near future.

A cadmium tungstate crystal scintillator enriched in 106 Cd was developed for an experiment to search for double beta processes in 106 Cd. With this aim samples of cadmium with natural isotopic composition and enriched in 106 Cd were purified by vacuum distillation. Cadmium tungstate compounds were synthesized from solutions. The absolute isotopic composition of the enriched cadmium was accurately determined as 66.4% by thermal ionisation mass-spectrometry. A 106 CdWO 4 crystal boule was grown by the low-thermal-gradient Czochralski technique. The total irrecoverable loss of the enriched cadmium in all the stages of the crystal scintillator production does not exceed 2.3%. The produced 106 CdWO 4 crystal scintillator with mass of 216 g exhibits good optical and scintillation properties.

We have studied the energy resolution, α / β ratio, temperature dependence of the scintillation properties, and the radioactive contamination of CaMoO4 crystal scintillators. We have also examined the use of pulse-shape discrimination to distinguish γ rays and α particles. A high sensitivity experiment to search for the 0 ν 2 β decay of Mo 100 using CaMoO4 scintillators is discussed.

A cadmium tungstate crystal boule enriched in $^{116}$Cd to 82% with mass of 1868 g was grown by the low-thermal-gradient Czochralski technique. The isotopic composition of cadmium and the trace contamination of the crystal were estimated by High Resolution Inductively Coupled Plasma Mass-Spectrometry. The crystal scintillators produced from the boule were subjected to characterization that included measurements of transmittance and energy resolution. A low background scintillation detector with two $^{116}$CdWO$_4$ crystal scintillators (586 g and 589 g) was developed. The detector was running over 1727 h deep underground at the Gran Sasso National Laboratories of the INFN (Italy), which allowed to estimate the radioactive contamination of the enriched crystal scintillators. The radiopurity of a third $^{116}$CdWO$_4$ sample (326 g) was tested with the help of ultra-low background high purity germanium $\gamma$ detector. Monte Carlo simulations of double $\beta$ processes in $^{116}$Cd were used to estimate the sensitivity of an experiment to search for double $\beta$ decay of $^{116}$Cd., Comment: 24 pages, 13 figures, 3 tables, accepted for publication on Journal of Instrumentation

An experiment to search for double beta processes in 106Cd by using cadmium tungstate crystal scintillator enriched in 106Cd (106CdWO4) in coincidence with the four crystals HPGe detector GeMulti is in progress at the STELLA facility of the Gran Sasso underground laboratory of INFN (Italy). The 106CdWO4 scintillator is viewed by a low-background photomultiplier tube through a lead tungstate crystal light-guide produced from deeply purified archaeological lead to suppress gamma quanta from the photomultiplier tube. Here we report the first results of the experiment after 3233 hours of the data taking. A few new improved limits on double beta processes in 106Cd are obtained, in particular T1/2(2nuECb+) > 8.4e20 yr at 90% C.L.

Cadmium tungstate crystal scintillators enriched in 106Cd up to 66% (106CdWO4) and in 116Cd up to 82% (116CdWO4) have been developed. The low radioactive contamination of the crystals measured on the level of ≤ 1.5 mBq/kg (40K), ≤ 0.005 - 0.012 mBq/kg (226Ra), 0.04 - 0.07 mBq/kg (228Th) allows to carry out high sensitivity experiments to search for double beta processes in 106Cd and 116Cd.

Cadmium tungstate crystal scintillators enriched in 106Cd and 116Cd were developed. The produced scintillators exhibit good optical and scintillation properties, and a low level of radioactive contamination. Experiments to search for double beta decay of 106Cd and 116Cd are in progress at the Gran Sasso National Laboratories of the INFN (Italy). Prospects to further improve the radiopurity of the detectors by recrystallization are discussed., Comment: 9 pages, 1 figure (4 eps-figs), 1 table. Accepted for publication in Radiation Measurements as a Proceedings of the 8th International Conference on Luminescent Detectors and Transformers of Ionizing Radiation (LUMDETR 2012), September 09-14, 2012, Halle (Saale), Germany

Cadmium tungstate crystal scintillators enriched in 106Cd (106CdWO 4 ) and 116Cd (116CdWO 4 ) have been developed to search for 2β-decay of 106Cd and 116Cd.

A search for double $\ensuremath{\beta}$ processes in ${}^{106}$Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) with the help of a ${}^{106}$CdWO${}_{4}$ crystal scintillator (215 g) enriched in ${}^{106}$Cd up to 66$%$. After 6590 h of data taking, new improved half-life limits on the double $\ensuremath{\beta}$ decay processes in ${}^{106}$Cd were established at the level of ${10}^{19}$--${10}^{21}$ yr; in particular, ${T}_{1/2}^{2\ensuremath{\nu}\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}}\ensuremath{\geqslant}2.1\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, ${T}_{1/2}^{2\ensuremath{\nu}2{\ensuremath{\beta}}^{+}}\ensuremath{\geqslant}4.3\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, and ${T}_{1/2}^{0\ensuremath{\nu}2\ensuremath{\varepsilon}}\ensuremath{\geqslant}1.0\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr. The resonant neutrinoless double-electron captures to the 2718-, 2741-, and 2748-keV excited states of ${}^{106}$Pd are restricted to ${T}_{1/2}^{0\ensuremath{\nu}2K}\ensuremath{\geqslant}4.3\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, ${T}_{1/2}^{0\ensuremath{\nu}K{L}_{1}}\ensuremath{\geqslant}9.5\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, and ${T}_{1/2}^{0\ensuremath{\nu}K{L}_{3}}\ensuremath{\geqslant}4.3\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, respectively (all limits at 90$%$ confidence level). A possible resonant enhancement of the $0\ensuremath{\nu}2\ensuremath{\varepsilon}$ processes is estimated in the framework of the quasiparticle random phase approximation (QRPA) approach. Radioactive contamination of the ${}^{106}$CdWO${}_{4}$ crystal scintillator is reported.

Several experiments were performed during last years at underground (3600 m w.e.) Laboratori Nazionali del Gran Sasso (LNGS) of the INFN (Italy) to search for resonant 2$\varepsilon0\nu$ captures in 96Ru, 106Cd, 136Ce, 156Dy, 158Dy, 180W, 184Os, 190Pt with the help of HP Ge semiconductor detectors, and ZnWO4 and 106CdWO4 crystal scintillators. No evidence for r-2$\varepsilon0\nu$ decays was found, and only T_{1/2} limits were established in the range of 10^{14}-10^{21} yr., Comment: Proceedings of TAUP 2011 Conference

A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using the Stockbarger growth technique. The crystal was subjected to a characterization that includes relative photoelectron output and energy resolution for gamma quanta. The intrinsic radioactivity of the SrI2(Eu) crystal scintillator was tested both by using it as scintillator at sea level and by ultra-low background HPGe gamma spectrometry deep underground. The response of the SrI2(Eu) detector to alpha particles (alpha/beta ratio and pulse shape) was estimated by analysing the 226Ra internal trace contamination of the crystal. We have measured: alpha/beta=0.55 at E_alpha=7.7 MeV, and no difference in the time decay of the scintillation pulses induced by alpha particles and gamma quanta. The application of the obtained results in the search for the double electron capture and electron capture with positron emission in 84Sr has been investigated at a level of sensitivity: T_1/2 \sim 10^{15}-10^{16} yr. The results of these studies demonstrate the potentiality of this material for a variety of scintillation applications, including low-level counting experiments., 24 pages, 12 figures, 4 tables, accepted for publication on Nucl. Instrum. Meth. A

Magnesium tungstate (MgWO4) crystals of ~1 cm3 volume were obtained for the first time using a flux growth technique. The crystal was subjected to comprehensive characterisation that included room-temperature measurements of the transmittance, X-ray luminescence spectra, afterglow under X-ray excitation, relative photoelectron output, energy resolution, non-proportionality of scintillation response to γ-quanta, response to α-particles, and pulse shape for γ-quanta and α-particles. The light output and decay kinetics of MgWO4 were studied over the temperature range 7-305 K. Under X-ray excitation the crystal exhibits an intense luminescence band peaking at a wavelength of 470 nm; the intensity of afterglow after 20 ms is 0.035%. An energy resolution of 9.1% for 662 keV γ-quanta of 137Cs was measured with a small (≈0.9 g) sample of the MgWO4 crystal. The photoelectron output of the MgWO4 crystal scintillator is 35% that of CdWO4 and 27% that of NaI(Tl). The detector showed pulse-shape discrimination ability in measurements with α-particles and γ-quanta, which enabled us to assess the radioactive contamination of the scintillator. The results of these studies demonstrate the prospect of this material for a variety of scintillation applications, including rare event searches. © 2008 Elsevier B.V.

Cadmium tungstate crystal scintillators enriched in $^{116}$Cd to 82% ($^{116}$CdWO$_4$, total mass of $\approx$1.2 kg) are used to search for 2$\beta$ decay of $^{116}$Cd deep underground at the Gran Sasso National Laboratory of the INFN (Italy). The radioactive contamination of the $^{116}$CdWO$_4$ crystals has been studied carefully to reconstruct the background of the detector. The measured half-life of $^{116}$Cd relatively to 2$\nu$2$\beta$ decay is $T^{2\nu2\beta}_{1/2}$ = [2.8 $\pm$ 0.05(stat.) $\pm$ 0.4(syst.)] $\times$ 10$^{19}$ yr, in agreement with the results of previous experiments. The obtained limit on the 0$\nu$2$\beta$ decay of $^{116}$Cd (considering the data of the last 8696 h run with an advanced background 0.12(2) counts/yr/kg/keV in the energy interval 2.7-2.9 MeV) is $T_{1/2} \ge 1.0 \times 10^{23}$ yr at 90% C.L. The sensitivity of the experiment to the $0\nu2\beta$ process is $\lim T_{1/2} = 3 \times 10^{23}$ yr at 90% C.L. over 5 years of the measurements and it can be advanced (by further reduction of the background by a factor 3-30) to the level of $\lim T_{1/2} = (0.5-1.5) \times 10^{24}$ yr for the same period of the data taking., Comment: Contribution to Proc. of Int. Workshop on Radiopure Scintillators RPSCINT 2013, 17-20.09.2013, Kyiv, Ukraine; to be published in EPJ Web of Conferences; 4 pages, 1 figure and 3 tables

A search for double ? processes in 106Cd was carried out at the Gran Sasso National Laboratories of the INFN, Italy; by using a CdWC4 crystal scintillator (mass of 215 g) enriched in 106Cd up to 66%. After 6590 h of data taking, half-life limits on double beta processes in 106Cd were set at level of 1019 ? 1021 yr. A possible resonant enhancement of the 0?2? processes has also been estimated in the framework of the QRPA approach.

AMoRE (Advanced Mo based Rare process Experiment) collaboration is going to use calcium molybdate crystals as cryogenic scintillation detector in a search for neutrinoless DBD of 100Mo isotope. Simultaneous detection of phonons and light will be used to reject internal background. A FWHM resolution of 0.2% in the phonon channel has been achieved with a 0.5 cm3 crystal. Several 40Ca100MoO4 crystals (≈ 0.5 kg) have been developed from enriched 100Mo and depleted 40Ca materials. The light yield of these crystals has been shown to be comparable with reference CaMoO4 scintillators for temperatures ranging down to 8 K. The content of dangerous radioisotopes in the crystals is under measurement. The projected sensitivity of the experiment for a 250 kg × years exposure is lim T1/2 ~ 3 × 1026 years, which corresponds to the effective Majorana neutrino mass mv ~ 0.02 – 0.06 eV.

EURECA (European Underground Rare Event Calorimeter Array) is an astro-particle physics facility aiming to directly detect galactic dark matter. The Laboratoire Souterrain de Modane has been selected as host laboratory. The EURECA collaboration unites CRESST, EDELWEISS and the Spanish-French experiment ROSEBUD, thus concentrating and focussing effort on cryogenic detector research in Europe into a single facility. EURECA will use a target mass of up to one ton, enough to explore WIMP - nucleon scalar scattering cross sections in the region of 10-9 - 10-10 picobarn. A major advantage of EURECA is the planned use of more than just one target material (multi target experiment for WIMP identification). © EAS, EDP Sciences 2009.