Search

In this work, a first cryogenic characterization of a scintillating $$\hbox {LiAlO}_{2}$$ LiAlO 2 single crystal is presented. The results achieved show that this material holds great potential as a target for direct dark matter search experiments. Three different detector modules obtained from one crystal grown at the Leibniz-Institut für Kristallzüchtung (IKZ) have been tested to study different properties at cryogenic temperatures. Firstly, two 2.8 g twin crystals were used to build different detector modules which were operated in an above-ground laboratory at the Max Planck Institute for Physics (MPP) in Munich, Germany. The first detector module was used to study the scintillation properties of $$\hbox {LiAlO}_{2}$$ LiAlO 2 at cryogenic temperatures. The second achieved an energy threshold of ($$213.02\pm 1.48$$ 213.02 ± 1.48 ) eV which allows setting a competitive limit on the spin-dependent dark matter particle-proton scattering cross section for dark matter particle masses between $$350\,\hbox {MeV/c}^{2}$$ 350 MeV/c 2 and $$1.50\,\hbox {GeV/c}^{2}$$ 1.50 GeV/c 2 . Secondly, a detector module with a 373 g $$\hbox {LiAlO}_{2}$$ LiAlO 2 crystal as the main absorber was tested in an underground facility at the Laboratori Nazionali del Gran Sasso (LNGS): from this measurement it was possible to determine the radiopurity of the crystal and study the feasibility of using this material as a neutron flux monitor for low-background experiments.

The X-ray luminescence and scintillation properties of undoped ZnTe crystal were investigated as function of temperature down to T130Te.

Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) is a long-standing direct dark matter detection experiment with cryogenic detectors located at the underground facility Laboratori Nazionali del Gran Sasso in Italy. CRESST-III, the third generation of CRESST, was specifically designed to have a world-leading sensitivity for low-mass dark matter (DM) (less than 2 GeV/$$\hbox {c}^{2}$$c2) to probe the spin-independent DM-nucleus cross section. At present, a large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below few GeV/$$\hbox {c}^{2}$$c2 although many motivated theoretical models having been proposed. The CRESST-III experiment employs scintillating $$\hbox {CaWO}_{{4}}$$CaWO4 crystals of $$\sim$$∼ 25 g as target material for dark matter interactions operated as cryogenic scintillating calorimeters at $$\sim$$∼ 10 mK. CRESST-III first data taking was successfully completed in 2018, achieving an unprecedented energy threshold for nuclear recoils. This result extended the present sensitivity to DM particles as light as $$\sim$$∼ 160 MeV/$$\hbox {c}^{2}$$c2. In this paper, an overview of the CRESST-III detectors and results will be presented.

In this work, we want to highlight the potential of lithium as a target for spin-dependent dark matter search in cryogenic experiments, with a special focus on the low-mass region of the parameter space. We operated a prototype detector module based on a $$\hbox {Li}_2\hbox {MoO}_4$$ target crystal in an above-ground laboratory. Despite the high background environment, the detector sets a competitive limit on spin-dependent interactions of dark matter particles with protons and neutrons for masses between $$0.8~\hbox {GeV/c}^2$$ and $$1.5~\hbox {GeV/c}^2$$ .

The CRESST-III experiment searches for direct interactions of dark matter with ordinary matter. The main event signature would be a nuclear recoil inside one of the scintillating CaWO4 crystals. Operating the crystals as cryogenic calorimeters provides a phonon signal as measure of the deposited energy. The simultaneous readout of both signals is used to actively discriminate backgrounds. CRESST-III focuses on the sub-GeV/c2 mass region where the sensitivity is driven by the threshold. In the first data taking campaign of CRESST-III from 2016-2018 an unprecedented low threshold of 30.1 eV for nuclear recoils was obtained. In this contribution, we will report the status of the experiment and the latest results.

In the current direct dark matter search landscape, the leading experiments in the sub-GeV mass region mostly rely on cryogenic techniques which employ crystalline targets. One attractive type of crystals for these experiments is those containing lithium, due to the fact that $$^7\hbox {Li}$$7Li is an ideal candidate to study spin-dependent dark matter interactions in the low mass region. Furthermore, $$^6\hbox {Li}$$6Li can absorb neutrons, a challenging background for dark matter experiments, through a distinctive signature which allows the monitoring of the neutron flux directly on site. In this work, we show the results obtained with three different detectors based on $$\hbox {LiAlO}_2$$LiAlO2, a target crystal never used before in cryogenic experiments.

The aim of this work is optimization of light collection in conditions similar to that in cryogenic scintillating bolometers. Energy resolution and relative pulse amplitude of scintillation detectors were measured using CaWO4 crystals with different shapes (cylindrical, hexagonal, cube and triangle prism), reflector materials and shapes, optical contact and surface conditions (polished and diffuse). Light collection was simulated using the ZEMAX ray-tracing software. The results of the simulations are in good agreement with the measured values of light output. Scintillators in the shape of a triangular prism with diffused surface surrounded by an external mirror shaped as truncated cone provide the highest light collection efficiency.

A search for double electron capture ($2\varepsilon$), electron capture with positron emission ($\varepsilon\beta^+$), and double positron emission $2\beta^+$) in $^{136}$Ce and $^{138}$Ce was realized with a 465 cm$^3$ ultra-low background HP Ge $\gamma$ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of $\gamma$ quanta expected in double $\beta$ decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double $\beta$ decay of $^{136}$Ce and $^{138}$Ce at the level of $T_{1/2}>10^{17}-10^{18}$ yr.

Double beta decay of $^{116}$Cd has been investigated with the help of radiopure enriched $^{116}$CdWO$_4$ crystal scintillators in the experiment Aurora. The half-life of $^{116}$Cd relatively to the 2$\nu$2$\beta$ decay of $^{116}$Cd to the ground level of $^{116}$Sn is measured with the highest up-to-date accuracy as $T_{1/2}$ = [2.69 $\pm$ 0.02 (stat.) $\pm$ 0.14 (syst.)] $\times$ 10$^{19}$ yr. A new improved limit on the 0$\nu$2$\beta$ decay of $^{116}$Cd to the ground state of $^{116}$Sn is set as $T_{1/2}\geq 2.4 \times 10^{23}$ yr at 90\% C.L., that corresponds to the effective Majorana neutrino mass limit in the range $\langle$$m_\nu$$\rangle$ $\le$ $(1.1-1.6)$ eV, depending on the nuclear matrix elements used in the estimations. New improved limits on other $2\beta$ processes in $^{116}$Cd (decays with majoron emission, transitions to excited levels of $^{116}$Sn) were set at the level of $T_{1/2}\geq 10^{21}-10^{22}$ yr., Comment: 4 pages, 2 figures

An experiment to search for double beta decay in 106Cd is running in the DAMA/CRYS set-up at the Gran Sasso National Laboratory of the INFN (Italy). In this experiment a 106CdWO4 crystal scintillator (215 g) enriched in 106Cd to 66%, used in previous measurements in different configurations, is now in measurement in coincidence with two large volume low background CdWO4 crystal scintillators in close geometry. This further measurement will allow us to reach a sensitivity at the level of the most sensitive double β+ experiments (T1/2 ≃ 1020 −1022 yr) and to explore the region of the theoretical expectations for some decay modes.An experiment to search for double beta decay in 106Cd is running in the DAMA/CRYS set-up at the Gran Sasso National Laboratory of the INFN (Italy). In this experiment a 106CdWO4 crystal scintillator (215 g) enriched in 106Cd to 66%, used in previous measurements in different configurations, is now in measurement in coincidence with two large volume low background CdWO4 crystal scintillators in close geometry. This further measurement will allow us to reach a sensitivity at the level of the most sensitive double β+ experiments (T1/2 ≃ 1020 −1022 yr) and to explore the region of the theoretical expectations for some decay modes.

The original version of this article unfortunately contains mistakes.

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.

Simulations of photon propagation in scintillation detectors were performed with the aim to find the optimal scintillator geometry, surface treatment, and shape of external reflector in order to achieve maximum light collection efficiency for detector configurations that avoid direct optical coupling, a situation that is commonly found in cryogenic scintillating bolometers in experimental searches for double beta decay and dark matter. To evaluate the light collection efficiency of various geometrical configurations we used the ZEMAX ray-tracing software. It was found that scintillators in the shape of a triangular prism with an external mirror shaped as truncated cone gives the highest light collection efficiency. The results of the simulations were confirmed by carrying out measurements of the light collection efficiencies of CaWO4 crystal scintillators. A comparison of simulated and measured values of light output shows good agreement. © 2014 Elsevier B.V. All rights reserved.

The scintillation properties of a zinc tungstate crystal, shaped as a hexagonal prism (height 40 mm, diagonal 40 mm) were determined. An energy resolution of 10.7% for the 662 keV γ-line of 137Cs was measured with the scintillator placed in a light collection setup similar to that used by the CRESST dark matter search. The light output and decay kinetics of ZnWO4 were examined over the temperature range 7-300 K and confirmed to be competitive with those of CaWO4. The radioactive contaminations of the ZnWO4 scintillator measured in the Solotvina Underground Laboratory do not exceed 0.1-10 mBq/kg (depending on radionuclide). Our study highlights the excellent feasibility of this ZnWO4 scintillator for a cryogenic dark matter experiment. © 2008 Elsevier B.V. All rights reserved.

A radiopure cadmium tungstate crystal scintillator, enriched in $^{106}\mathrm{Cd}$ to 66%, with mass of 216 g $(^{106}\mathrm{Cd}{\text{WO}}_{4})$, was used to search for double-$\ensuremath{\beta}$ decay processes in $^{106}\mathrm{Cd}$ in coincidence with four ultra-low-background high-purity germanium detectors in a single cryostat. Improved limits on the double-$\ensuremath{\beta}$ processes in $^{106}\mathrm{Cd}$ have been set on the level of ${10}^{20}\ensuremath{-}{10}^{21}$ yr after 13 085 h of data taking. In particular, the half-life limit on the two-neutrino electron capture with positron emission, ${T}_{1/2}^{2\ensuremath{\nu}\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}}\ensuremath{\ge}1.1\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr, has reached the region of theoretical predictions. With this half-life limit the effective nuclear matrix element for the $2\ensuremath{\nu}\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}$ decay is bounded as ${M}_{\mathrm{eff}}^{2\ensuremath{\nu}\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}}\ensuremath{\le}1.1$. The resonant neutrinoless double-electron captures to the 2718-, 2741-, and 2748-keV excited states of $^{106}\mathrm{Pd}$ are restricted at the level of ${T}_{1/2}\ensuremath{\ge}(8.5\ifmmode\times\else\texttimes\fi{}{10}^{20}\ensuremath{-}1.4\ifmmode\times\else\texttimes\fi{}{10}^{21})$ yr.

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 tables

A radiopure cadmium tungstate crystal scintillator, enriched in 106 Cd to 66%, with mass of 216 g (106CdWO4) was used in coincidence with four ultra-low background HPGe detectors contained in a single cryostat to search for double beta (2β) decay processes in 106 Cd. New improved half-life limits on the 2β processes in 106 Cd have been set on the level of 1020 — 1021 yr after 13085 h of data taking deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (Italy). In particular, the limit on the two neutrino electron capture with positron emission, Teβ+2 1/2≥ 1.1 × 1021 yr, has reached the region of theoretical predictions. The resonant neutrinoless double electron captures to the 2718, 2741 and 2748 keV excited states of 106 Pd are restricted on the level of T2e0v 1/2 ≥ (8.5 × 1020 - 1.4 × 1021) yr.

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.

In June–August 2006 an expedition with the aim to look for archaeological lead with low levels of 210 Pb was organised by a Korean–Ukrainian collaboration on the shelf of the Black Sea, near the Crimean Peninsula. The first samples with ∼0.2 ton of total mass were found at a depth of 28 m among the relics of an ancient Greek ship. Their age has been dated to the first century BC. The element composition of the samples was measured by means of X-ray fluorescence and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analyses. The radiopurity of the lead was tested using low-level and ultra-low-level γ-spectrometry at a surface laboratory in Kyiv, at the Solotvina Underground Laboratory (Ukraine), and deep underground at the Laboratori Nazionali del Gran Sasso (LNGS, Italy). The samples have been assessed at the LNGS also by means of α-spectroscopy. For all investigated radionuclides, only upper limits could be obtained. Limits on activities of radionuclides in the lead after melting were set at the level of −1 ( 60 Co), −1 ( 137 Cs), −1 ( 226 Ra), −1 ( 228 Th), −1 ( 40 K), −1 ( 210 Po), and −1 ( 210 Pb). Any 210 Pb present in the lead after it was produced ca. 2000 years ago has decayed away. Assuming secular equilibrium in the 238 U chain in the lead, the activity of 210 Pb due to 238 U can be restricted to −1 before melting, and −1 after melting.

Large volume zinc tungstate crystal scintillators (up to 50 mm in diameter and 100 mm length) with improved energy resolution were developed as a result of advances in crystal growth. The energy resolution of one-centimeter cube ZnWO4 crystals showed energy resolution in the range 8-10% for 662 keV gamma line of 137Cs. A value of 13.7% has been obtained with a large sample Oslash44 times 55 mm. The radioactive contamination of a ZnWO4 26 times 24 times 24 mm detector was tested in the Solotvina Underground Laboratory. The obtained results demonstrate ability to use ZnWO4 in order to search for 2beta-decay of zinc and tungsten.

Light output, α / β ratio, and pulse shape have been investigated at - 25 ∘ C with PbWO 4 crystal scintillators undoped, and doped by F, Eu, Mo, Gd and S. The fast 0.01– 0.06 μ s and middle 0.1– 0.5 μ s components of scintillation decay were observed for all the samples. Slow components of scintillation signal with decay times 1–3 and 13– 28 μ s with total intensity up to ≈ 50 % have been recognized for several samples doped by Molybdenum. We found some indications of a pulse-shape discrimination between α particles and γ quanta with PbWO 4 (Mo doped) crystal scintillators.

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.

Some recent results obtained in the search for double beta decay in vari- ous isotopes obtained in experiments carried out at LNGS with the DAMA/R&D, DAMA/Ge set-up and the STELLA facility will be summarized.

A radiopure cadmium tungstate crystal scintillator, enriched in 106Cd (106CdWO4), was used to search for double beta decay processes in 106Cd in coincidence with an ultra-low background set-up containing four high purity germanium (HPGe) detectors in a single cryostat. The experiment has been completed after 13085 h of data taking. New improved limits on most of the double beta processes in 106Cd have been set on the level of 1020−1021 yr. Tn particular, the half-life limit on the two neutrino electron capture with positron emission, T1/2 ≥ 1.8 × 1021 yr, reached the region of theoretical predictions.

An experiment to search for 2β processes in 116Cd with the help of enriched (to 82%) cadmium tungstate crystal scintillators is in progress at the Gran Sasso National Laboratory of the INFN (LNGS, Italy). After 11074 h of data taking in the last configuration, the preliminary estimate for the half-life of 116Cd relatively to 2ν2β decay is T1/2 = [2.52 ± 0.02(stat.) ± 0.14(syst.)] × 1019 yr. By using the data of previous stages of the experiment with a similar level of background (≈ 0.1 counts/(keV kg yr) in the energy interval 2.7 – 2.9 MeV; the total time of measurements is 19770 h) we have obtained a new limit on the 0ν2β decay of 116Cd to the ground state of 116Sn: T1/2 ≥ 1.9 × 1023 yr at 90% C.L. New limits on different 2β processes in 116Cd (decays with majorons, transitions to the excited levels) are obtained on the level of T1/2 ≥ 1020 – 1022 yr.

International audience; 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.

The purpose of this work is to study the possibility to improve light collection in conditions similar to than in cryogenic scintillating bolometers. Energy resolution and relative pulse amplitude of scintillation detectors were measured using CaWO 4 crystals with different shapes (cylindrical, hexagonal and cube prism), reflector materials and shapes, optical contact and surface conditions (polished and diffused). Light collection was simulated using ZEMAX codes.

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.

Cerium, neodymium and gadolinium contain double beta active isotopes. The most interesting are 150 Nd and 160 Gd (promising for 02 search), 136 Ce (2 + candidate with one of the highest Q 2). The main problem of compounds containing lanthanide elements is their high radioactive contamination by uranium, radium, actinium and thorium. The new generation 2 experiments require development of methods for a deep purification of lanthanides from the radioactive elements. A combination of physical and chemical methods was applied to purify cerium, neodymium and gadolinium. Liquid-liquid extraction technique was used to remove traces of Th and U from neodymium, gadolinium and for purification of cerium from Th, U, Ra and K. Co-precipitation and recrystallization methods were utilized for further reduction of the impurities. The radioactive contamination of the samples before and after the purification was tested by using ultra-low- background HPGe gamma spectrometry. As a result of the purification procedure the radioactive contamination of gadolinium oxide (a similar purification efficiency was reached also with cerium and neodymium oxides) was decreased from 0.12 Bq/kg to 0.007 Bq/kg in 228 Th, from 0.04 Bq/kg to

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.

100 Mo abstract Zinc molybdate (ZnMoO4) crystals are an excellent candidate material to fabricate scintillating bolometers for the study of neutrinoless double beta decay of 100 Mo, provided that the crystal quality meets strict optical, thermal and radiopurity requirements. This paper addresses the characterization of improved crystalline samples grown by the low-thermal-gradient Czochralski technique. Transmittance measurements confirm significant improvement of the material with respect to previously developed samples. Luminescence properties (emission spectra, dependence of intensity on temperature, thermally stimulated luminescence and phosphorescence) have been studied under X-ray excitation from liquid- helium to room temperature. The index of refraction was measured in the wavelength interval 406- 655 nm. Samples of ZnMoO4 crystals with masses of 5.07 g and 23.8 g were operated as scintillating bolometers at temperatures below 30 mK, with simultaneous detection of scintillation and heat signals, confirming an excellent alpha/beta rejection power. Background measurements allowed encouraging radiopurity level estimations. The light collection from ZnMoO4 scintillators was Monte Carlo simulated, analysing different crystal size, shape and surface properties and different photodetector sizes.

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

The studies performed in the research of new materials and purification techniques allow us a wide choice among inorganic scintillators for a variety of use. In this paper crystal scintillators and their application and potentialities in low background measurements are discussed, with a particular attention to direct dark matter investigation.

There are several potentially double beta active isotopes among the lanthanide elements. However, even high purity grade lanthanide compounds contain 238U, 226Ra and 232,228Th typically on the level of ∼ (0.1 - 1) Bq/kg. The liquid-liquid extraction technique was used to remove traces of U, Ra and Th from CeO2, Nd2O3 and Gd2O3. The radioactive contamination of the samples before and after the purification was tested by using ultra-low-background HPGe γ spectrometry at the underground Gran Sasso National Laboratories of the INFN (Italy). After the purification the radioactive contamination of gadolinium oxide by Ra and Th was decreased at least one order of magnitude. The efficiency of the approach to purify cerium oxide from Ra was on same level, while the radioactive contamination of neodymium sample before and after the purification is below the sensitivity of analytical methods. The purification method is much less efficient for chemically very similar radioactive elements like lanthanum, lutetium and ...

The Aurora experiment to investigate double beta decay of $^{116}$Cd with the help of 1.162 kg cadmium tungstate crystal scintillators enriched in $^{116}$Cd to 82\% is in progress at the Gran Sasso Underground Laboratory. The half-life of $^{116}$Cd relatively to the two neutrino double beta decay is measured with the highest up-to-date accuracy $T_{1/2}=(2.62\pm0.14)\times10^{19}$ yr. The sensitivity of the experiment to the neutrinoless double beta decay of $^{116}$Cd to the ground state of $^{116}$Sn is estimated as $T_{1/2} \geq 1.9\times10^{23}$ yr at 90\% CL, which corresponds to the effective Majorana neutrino mass limit $\langle m_{\nu}\rangle \leq (1.2-1.8)$ eV. New limits are obtained for the double beta decay of $^{116}$Cd to the excited levels of $^{116}$Sn, and for the neutrinoless double beta decay with emission of majorons., Comment: 5 pages, 3 figures, 1 table, submitted as proceedings of the TAUP 2015 conference

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

Feasibility studies on a search for 7 Li solar axion have been carried out. In particular, the data collected with a LiF powder of 243 g measured during 722 h with a 408 cm 3 low background HP Ge detector (GSOR) at the Gran Sasso National Laboratories (LNGS) of INFN has allowed to set limit on the 7 Li solar axion mass of 13.9 keV, better than the previously available one: 16.0 keV [A.V. Derbin, et al., JETP Lett. 81 (2005) 365]. It has also been shown that improved results would be achieved with LiF(W) crystal which—in contrast with the LiF powder—does not show a relatively high contamination by U/Th chains. The potential backgrounds and the reachable sensitivity of an experiment are discussed.

Large volume zinc tungstate crystal scintillators with improved scintillation characteristics were produced. Energy resolution and relative light output of samples with various sizes and shapes (cylinders, rectangular, and hexagonal prisms) were investigated. The energy resolutions of ZnWO4 scintillator modules for the 662 keV gamma line of 137Cs were 8.5% for a 1 cm3 sample and 10.7% for the large hexagonal module of dimensions diam 40 times 40 mm. A variation of the light output by 7%, depending on direction of observation was found for the 1 cm3 cubic crystal. Afterglow, measured 20 ms after termination of irradiation, was 0.002%. The relative light output of the scintillator and the decay kinetics were studied over the temperature range 7-300 K. The level of radioactive contamination of the ZnWO4 scintillator was determined in the Solotvina Underground Laboratory at a sensitivity of ap0.1-10 mBq/kg.

Double beta processes in 64Zn, 70Zn, 180W, and 186W have been searched for with the help of large volume (0.1–0.7 kg) low background ZnWO4 crystal scintillators at the Gran Sasso National Laboratories of the INFN (Italy). The total measurement time exceeds ten thousand hours. New improved half-life limits on double electron capture and electron capture with positron emission in 64Zn have been set, in particular (all the limits are at 90% C.L.): T 1 / 2 0 ν 2 e ⩾ 1.1 × 10 20 yr , T 1 / 2 2 ν e β + ⩾ 7.0 × 10 20 yr , and T 1 / 2 0 ν e β + ⩾ 4.3 × 10 20 yr . In addition, new T 1 / 2 bounds were set for different modes of 2β processes in 70Zn, 180W, and 186W at the level of 1017–1020 yr.

Results are presented of our latest research, aimed at the development and study of oxide scintillation crystals with high scintillation yield and low intrinsic radioactivity. We report on the improvement of these properties for conventional scintillators, as well as on new promising crystals based on metal tungstates and molybdates. The results are discussed in view of applying these materials in cryogenic experiments searching for dark matter or neutrinoless double beta decay. ©2008 IEEE.

In June‐August 2006 an expedition with the aim to look for low‐radioactive archaeological lead at the bottom of the Black Sea, near the Crimean peninsula (Ukraine) was organised by a Korean‐Ukrainian collaboration. The first samples with ∼0.2 tons of total mass were found at a depth of 28 m among the relics of an ancient Greek ship. Their age has been dated to the first century B.C. This lead was used as ballast in the keel of the ship. The element composition of the samples was measured by means of X‐ray fluorescence and ICP‐MS analyses. The first preliminary limits on the 210Pb contamination of the samples are less than a few hundreds mBq/kg. The measurements were performed using gamma spectroscopy with HPGe‐detectors and alpha spectroscopy with commercial α‐detectors. Measurements of 40K, Th/U in the lead samples were undertaken in Kiev and in the underground laboratories of the Laboratori Nazionali del Gran Sasso (LNGS, Italy). If it was found to be radio‐clean this lead could be used as high efficien...

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.

High light collection efficiency is an important requirement in any application of scintillation detectors. The purpose of this study is to investigate the possibility for improving this parameter in cryogenic scintillation bolometers, which can be considered as a promising detectors in experiments investigating neutrinoless double beta decay and dark matter. Energy resolutions and relative pulse amplitudes of scintillation detectors using ZnWO4 scintillation crystals of different shapes (cylinder 20 mm in dimater by 20 mm and hexagonal prism with diagonal 20 mm and height 20 mm), reflector materials and shapes, optical contact and surface properties (polished and diffused) were measured at room temperature. Propagation of optical photons in these experimental conditions was simulated using Geant4 and ZEMAX codes. The results of the simulations are found to be in good agreement with each other and with direct measurements of the crystals. This could be applied to optimize the geometry of scintillation detectors used in the cryogenic experiments., 12 pages, 8 figures, 1 Table