Search

Neutrinoless double beta ($0\nu\beta\beta$) decay is a hypothetical rare nuclear transition ($T_{1/2}>10^{26}$ y). Its observation would provide an important insight about the nature of neutrinos (Dirac or Majorana particle) demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double beta decay isotope ($^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{116}$Cd, $^{130}$Te...), which perform as low temperature calorimeters (10 mK) detecting particle interactions via a small temperature rise read out by a dedicated thermometer. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at the development of bolometric detectors (Li$_{2}$MoO$_{4}$ and TeO$_{2}$) capable of discriminating surface $\alpha$ and $\beta$ interactions by exploiting superconducting properties of Al film deposited on the crystal surface. We report in this paper the results of tests on prototypes performed at CSNSM (Orsay, France) that showed the capability of a-few-$\mu$m-thick superconducting Al film deposited on crystal surface to discriminate surface $\alpha$ from bulk events, thus providing the detector with the required surface sensitivity capability. The CROSS technology would further improve the background suppression and simplify the detector construction with a view to future competitive double beta decay searches., Comment: Accepted for publication in J. Low Temp. Phys

The double-electron capture and the electron capture with positron emission in 168Yb have been investigated for the first time at the STELLA facility of the Gran Sasso underground laboratory (Italy) measuring 371 g of highly purified ytterbium oxide placed on the end-cap of a 465 cm3 ultra-low-background high purity Germanium detector (HPGe). No gamma associated to double beta processes in 168Yb have been observed after 2074 h of data taking. This has allowed setting the half-life limits on the level of lim ⁡ T 1 / 2 ∼ 10 14 – 10 18 yr at 90% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in 168Yb to the ( 2 ) − 1403.7 keV excited state of 168Er is set as T 1 / 2 ≥ 1.9 × 10 18 yr at 90% C.L. Half-life limits T 1 / 2 2 ν ( 0 ν ) ≥ 4.5 ( 4.3 ) × 10 16 yr were set on the 2 ν ( 0 ν ) 2 β − decay of 176Yb to the 2 + 84.3 keV first excited level of 176Hf.

Double-beta processes in $^{184}$Os and $^{192}$Os were searched for over 15851 h at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. by using a 118 g ultra-pure osmium sample installed on the endcap of a 112 cm$^3$ ultra-low-background broad-energy germanium detector. New limits on double-electron capture and electron capture with positron emission in $^{184}$Os were set at the level of $\lim T_{1/2} \sim 10^{16}-10^{17}$ yr. In particular the $2\nu$2K and $2\nu$KL decays of $^{184}$Os to the ground state of $^{184}$W are restricted as $T_{1/2}\geq3.0\times 10^{16}$ yr and $T_{1/2}\geq2.0\times 10^{16}$ yr, respectively. A lower limit on the half-life for the double-beta decay of $^{192}$Os to the first excited level of $^{192}$Pt was set as $\lim T_{1/2}=2.0\times 10^{20}$ yr at 90\% C.L., Comment: 22 pages, 9 figures, 2 tables

Lithium magnesium molybdate (Li 2 Mg 2 (MoO 4 ) 3 ) crystals were grown by the low-thermal-gradient Czochralski method . Luminescence properties of the material (emission spectra, thermally stimulated luminescence, dependence of intensity on temperature, phosphorescence) have been studied under X-ray excitation in the temperature interval from 8 to 400 K, while at the same being operated as a scintillating bolometer at 20 mK for the first time. We demonstrated that Li 2 Mg 2 (MoO 4 ) 3 crystals are a potentially promising detector material to search for neutrinoless double beta decay of 100Mo.

This paper reports on the development of a technology involving $$^{100}\hbox {Mo}$$ 100 Mo -enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass ( $$\sim 1~\hbox {kg}$$ ∼ 1 kg ), high optical quality, radiopure $$^{100}\hbox {Mo}$$ 100 Mo -containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2–0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the double-beta transition of $$^{100}\hbox {Mo}$$ 100 Mo (3034 keV) is 4–6 keV FWHM. The rejection of the $$\alpha $$ α -induced dominant background above 2.6 MeV is better than $$8\sigma $$ 8 σ . Less than $$10~\upmu \hbox {Bq/kg}$$ 10 μ Bq/kg activity of $$^{232}\hbox {Th}\, (^{228}\hbox {Th})$$ 232 Th ( 228 Th ) and $$^{226}\hbox {Ra}$$ 226 Ra in the crystals is ensured by boule recrystallization. The potential of $$^{100}\hbox {Mo}$$ 100 Mo -enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only $$10~\hbox {kg}\times \hbox {d}$$ 10 kg × d exposure: the two neutrino double-beta decay half-life of $$^{100}\hbox {Mo}$$ 100 Mo has been measured with the up-to-date highest accuracy as $$T_{1/2}$$ T 1 / 2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] $$\times ~10^{18}~\hbox {years}$$ × 10 18 years . Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of $$^{100}\hbox {Mo}$$ 100 Mo .

The CUPID-Mo experiment is searching for neutrinoless double beta decay in $^{100}$Mo, evaluating the technology of cryogenic scintillating Li$_{2}^{100}$MoO$_4$ detectors for CUPID (CUORE Upgrade with Particle ID). CUPID-Mo detectors feature background suppression using a dual-readout scheme with Li$_{2}$MoO$_4$ crystals complemented by Ge bolometers for light detection. The detection of both heat and scintillation light signals allows the efficient discrimination of $\alpha$ from $\gamma$&$\beta$ events. In this proceedings, we discuss results from the first 2 months of data taking in spring 2019. In addition to an excellent bolometric performance of 6.7$\,$keV (FWHM) at 2615$\,$keV and an $\alpha$ separation of better than 99.9\% for all detectors, we report on bulk radiopurity for Th and U. Finally, we interpret the accumulated physics data in terms of a limit of $T_{1/2}^{0\nu}\,> 3\times10^{23}\,$yr for $^{100}$Mo and discuss the sensitivity of CUPID-Mo until the expected end of physics data taking in early 2020., Comment: Proceedings for TAUP 2019, submitted to IOP Journal of Physics: Conference Series

International audience; Final results of studies of 116Cd 2β decay with CdWO4 crystal scintillators, enriched in 116Cd to 82%, are presented. After few years (2011 – 2017) of measurements with radiopure 116CdWO4 scintillators (mass of 1.162 kg) at the Gran Sasso underground laboratory (Italy), the half-life of 116Cd relatively to 2ν2β decay to the ground state of 116Sn was measured with the highest up-to-date accuracy as T1/2=(2.63−0.12+0.11)×1019 yr. A new limit on 0ν2β decay of 116Cd was set as T1/2≥2.2×1023 yr at 90% C.L., which is the most stringent to-date restriction for this isotope. Limits for 0ν2β decay with majoron(s) emission, Lorentz-violating 2ν2β decay and 2β transitions to excited states of 116Sn were set at the level of T1/2≥1020−1022 yr.

Two-neutrino 2β decay of 150Nd to the 01+ 740.5-keV excited level of 150Sm has been investigated by using a highly purified 2.381-kg Nd2O3 sample with the help of ultra-low-background gamma spectrometer with 4 HPGe detectors (≈ 255 cm3 each) at the Gran Sasso underground laboratory (INFN, Italy). Gamma quanta, expected in cascade after de-excitation of the 01+ (740.5 keV) excited level of 150Sm, have been observed in the coincidence spectra accumulated over 25947 h. The half-life value has been preliminary estimated as T1/2=[ 6.9−1.9+4.0(stat)±1.1(syst) ]×109y. The data taking is in progress to reduce the statistical error.Two-neutrino 2β decay of 150Nd to the 01+ 740.5-keV excited level of 150Sm has been investigated by using a highly purified 2.381-kg Nd2O3 sample with the help of ultra-low-background gamma spectrometer with 4 HPGe detectors (≈ 255 cm3 each) at the Gran Sasso underground laboratory (INFN, Italy). Gamma quanta, expected in cascade after de-excitation of the 01+ (740.5 keV) excited level of 150Sm, have been observed in the coincidence spectra accumulated over 25947 h. The half-life value has been preliminary estimated as T1/2=[ 6.9−1.9+4.0(stat)±1.1(syst) ]×109y. The data taking is in progress to reduce the statistical error.

International audience; Recent developments, results, and perspectives arising from double beta decay experiments at the Gran Sasso National Laboratory (LNGS) of the INFN by using HPGe detectors and crystal scintillators and by exploiting various approaches and different isotopes are summarized. The measurements here presented have been performed in the experimental set-ups of the DAMA collaboration. These setups are optimized for low-background studies and operate deep underground at LNGS. The presented results are of significant value to the field, and the sensitivity achieved for some of the considered isotopes is one of the best available to date.

The Majorana nature of neutrinos is one of the most important questions being pursued in physics today. This has given the search for neutrinoless double-beta decay (0 ν β β ) a high priority among proposed nuclear physics experiments. In this work, the objective was to evaluate several crystal compositions for possible use as a scintillating bolometer in 0 ν β β research. A crucial characteristic of the investigated crystals is that their compositions must include one of the few elements known to decay with double-beta emission. Therefore, we grew crystals containing molybdenum or selenium as a major constituent. Results are presented here for single-crystals of sodium molybdate and lithium indium diselenide. Scintillating bolometer data were measured at milli-Kelvin temperature and show good discrimination between alpha and beta/gamma emissions, which is crucial for background reduction. The lithium indium diselenide crystal was also used to measure the energy spectrum for the beta emission of indium decay, the first time a beta decay spectrum has been measured from self-emission in a scintillating bolometer.

Bolometers are low temperature particle detectors with high energy resolution and detection efficiency. Some types of bolometric detectors are also able to perform an efficient particle identification. A wide variety of radiopure dielectric and diamagnetic materials makes the bolometric technique favorable for applications in astroparticle physics. In particular, thanks to their superior performance, bolometers play an important role in the world-wide efforts on searches for neutrinoless double-beta decay. Such experiments strongly require an extremely low level of the backgrounds that can easily mimic the process searched for. Here we overview recent progress in the development of low background techniques for bolometric double-beta decay searches., Review, a part of IJMPA Special Issue on Low Background Techniques

Author(s): Novati, V; Artusa, DR; Avignone, FT; Beeman, JW; Dafinei, I; Dumoulin, L; Ge, Z; Giuliani, A; Gotti, C; de Marcillac, P; Marnieros, S; Nagorny, S; Nisi, S; Nones, C; Norman, EB; Olivieri, E; Orlandi, D; Pagnanini, L; Pattavina, L; Pessina, G; Pirro, S; Poda, DV; Rusconi, C; Schaffner, K; Scielzo, ND; Zhu, Y | Abstract: We present here an innovative cryogenic light detector capable to measure a few tens of eV signal thanks to the amplification assisted by the Neganov–Luke effect. The thermal signal boost in the presence of an electric field allows us to improve the signal-to-noise ratio reaching a baseline noise of around 20 eV. This device – coupled to an enriched 130TeO2 bolometer (435 g) – registered 160 eV Cherenkov light signal induced by 2615 keV 208Tl with a signal to noise ratio about 6:1. Since α particles emitted in decays of natural radionuclides do not produce the Cherenkov radiation, we were able to achieve an efficient α∕γ separation in the region of interest for neutrinoless double beta decay of 130Te (Q-value is 2527 keV). Specifically, a rejection factor of 99.9% for α particles was obtained with a 98.3% acceptance of β∕γ events. The achieved α rejection efficiency is required to reduce the dominant α background in the follow-up of the CUORE experiment (CUPID), a ton-scale bolometric search with particle identification.

Search for double $\beta$ decay of $^{136}$Ce and $^{138}$Ce was realized with 732 g of deeply purified cerium oxide sample measured over 1900 h with the help of an ultra-low background HPGe $\gamma$ detector with a volume of 465 cm$^3$ at the STELLA facility of the Gran Sasso National Laboratories of the INFN (Italy). New improved half-life limits on double beta processes in the cerium isotopes were set at the level of $\lim T_{1/2}\sim 10^{17}-10^{18}$~yr; many of them are even two orders of magnitude larger than the best previous results., Comment: 21 pages, 6 figures, 3 tables; version accepted for publication on Nucl. Phys. A

A large cylindrical cadmium molybdate crystal with natural isotopic abundance has been used to fabricate a scintillating bolometer. The measurement was performed above ground at milli-Kelvin temperature, with simultaneous readout of the heat and the scintillation light. The energy resolution as FWHM has achieved from 5 keV (at 238 keV) to 13 keV (at 2615 keV). We present the results of the α versus β / γ events discrimination. The low internal trace contamination of the CdMoO 4 crystal was evaluated as well. The detector performance with preliminary positive indications proves that cadmium molybdate crystal is a promising absorber for neutrinoless double beta decay scintillating bolometric experiments with 116 Cd and 100 Mo nuclides in the next-generation technique.

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.

We present the performances of two 92% enriched $^{130}$TeO$_2$ crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of $^{130}$Te. The crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV $\gamma$-line of $^{208}$Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from $^{238}$U (15 and 8 $\mu$Bq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, $^{226}$Ra and $^{228}$Th, are both evaluated as $

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.

Results are presented on our latest research, aimed at the development and study of oxide scintillation crystals (ZnWO4, ZnMoO4, PbWO4, PbMoO4, and MgWO4) 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 and/or neutrinoless double beta decay. © 2006 IEEE.

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.

International audience; The LUMINEU (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature) project envisages a high-sensitivity search for neutrinoless double beta (0 nu 2 beta) decay of Mo-100 with the help of scintillating bolometers based on zinc molybdate (ZnMoO4) crystals. One of the crucial points for the successful performance of this experiment is the development of a protocol for producing high quality large mass ZnMoO4 crystal scintillators with extremely high internal radiopurity. Here we report a significant progress in the development of large volume ZnMoO4 crystalline boules (with mass up to 1 kg) from deeply purified materials. We present and discuss the results achieved with two ZnMoO4 samples (with mass of about 0.3 kg each): one is a precursor of the LUMINEU project, while the other one was produced in the framework of LUMINEU with an improved purification / crystallization procedure. The two crystals were measured deep underground as scintillating bolometers in the EDELWEISS dilution refrigerator at the Laboratoire Souterrain de Modane (France) protected by a rock overburden corresponding to 4800 m w.e. The results indicate that both tested crystals are highly radiopure. However, the advanced LUMINEU sample shows a clear improvement with respect to the precursor, exhibiting only a trace internal contamination related with Po-210 at the level of 1 mBq/kg, while the activity of Ra-226 and Th-228 is below 0.005 mBq/kg. This demonstrates that the LUMINEU purification and crystal-growth procedures are very efficient and leads to radiopurity levels which exceedingly satisfy not only the LUMINEU goals but also the requirements of a next-generation 0 nu 2 beta experiment.

Lead tungstate (PbWO4) crystal scintillators are discussed as an active shield and light guides in Cd-116 double-beta decay experiment with Cadmium tungstate (CdWO4) scintillators. Scintillation properties and radioactive contamination of PbWO4 scintillators were investigated. Energy resolution of CdWO4 detector, coupled to PbWO4 light guide, was tested. Efficiency of PbWO4-based active shield to suppress background from the internal contamination of PbWO4 crystals, as well as possible contribution from radioactivity of copper shield and phototubes were calculated. Using of lead tungstate crystal scintillators as high-efficiency 4 pi active shield could allow to build sensitive 2 beta experiment (T-1/2(0 nu 2 beta) similar to 10(26) yr) to search for 0 nu 2 beta decay of Cd-116 with (CdWO4)-Cd-116 crystal scintillators. (c) 2005 Elsevier B.V. All rights reserved.

Energy resolution, α / β ratio, and the pulse shape discrimination ability of the ZnWO 4 crystal scintillators were studied. The radioactive contamination of a ZnWO 4 crystal was investigated in the Solotvina Underground Laboratory. Possibilities to apply ZnWO 4 crystals for the dark matter and double beta decay searches are discussed. New improved half-life limits on double beta decay in zinc isotopes were established, in particular, for ɛ β + decay of 64 Zn as: T 1 / 2 2 ν ⩾ 8.9 × 10 18 years and T 1 / 2 0 ν ⩾ 3.6 × 10 18 years, both at 68% CL.

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.

ISBN: 978-0-7354-1333-7; International audience; The LUMINEU program aims at performing a pilot experiment on 0ν2β decay of 100 Mo using radiopure ZnMoO4 crystals enriched in 100 Mo operated as cryogenic scintillating bolometers. Large volume ZnMoO4 crystal scintillators (∼ 0.3 kg) were developed and tested showing high performance in terms of radiopurity, energy resolution and α/β particle discrimination capability. Zinc molybdate crystal scintillators enriched in 100 Mo were grown for the first time by the low-thermal-gradient Czochralski technique with a high crystal yield and an acceptable level of enriched molybdenum irrecoverable losses. A background level of ∼ 0.5 counts/(yr keV ton) in the region of interest can be reached in a large detector array thanks to the excellent detectors radiopurity and particle discrimination capability, suppression of randomly coinciding events by pulse-shape analysis, and anticoincidence cut. These results pave the way to future sensitive searches based on the LUMINEU technology, capable of approaching and exploring the inverted hierarchy region of the neutrino mass pattern.

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.

The LUMINEU project is a demonstrator experiment that will search for the neutrinoless double beta decay of the isotope \(^{100}\)Mo embedded in zinc molybdate (ZnMoO\(_4\)) scintillating bolometers. In this context, a zinc molybdate crystal boule enriched in \(^{100}\)Mo to 99.5 % with a mass of 171 g was grown for the first time by the low-thermal-gradient Czochralski technique. The production cycle provided a high yield (the crystal boule mass was 84 % of the initial charge) and an acceptable level—around 4 %—of irrecoverable losses of the costly enriched material. Two crystals of 59 and 63 g, obtained from the enriched boule, were tested above ground at millikelvin temperatures as scintillating bolometers. They showed a good detection performance, equivalent to that of previously developed natural ZnMoO\(_4\) detectors. These results pave the way to future sensitive searches based on the LUMINEU technology, capable of approaching and exploring the inverted hierarchy region of the neutrino mass pattern.

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

Barium fluoride (BaF$_2$) crystal scintillators are promising detectors to search for double beta decay processes in $^{130}$Ba ($Q_{2{\beta}}$ = 2619(3) keV) and $^{132}$Ba ($Q_{2{\beta}}$ = 844(1) keV). The $^{130}$Ba isotope is of particular interest because of the indications on 2${\beta}$ decay found in two geochemical experiments. The radioactive contamination of BaF$_2$ scintillation crystal with mass of 1.714 kg was measured over 113.4 hours in a low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of $^{212}$Po (present in the crystal scintillator due to contamination by radium) was estimated as $T_{1/2}$ = 298.8 $\pm$ 0.8(stat.) $\pm$ 1.4(syst.) ns by analysis of the events pulse profiles., 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, 7 figure and 1 table

Results on the search for rare nuclear decays with the ultra low background facility STELLA at the LNGS using gamma ray spectrometry are presented. In particular, the best T1/2 limits were obtained for double beta processes in 96Ru and 104Ru. Several isotopes, which potentially decay through different double beta decay channels, including also possible resonant double electron captures, were investigated for the first time (156Dy, 158Dy, 184Os, 192Os, 190Pt, 198Pt). Search for resonant absorption of solar 7Li axions in a LiF crystal gave the best limit for the mass of 7Li axions (< 8.6 keV). Rare alpha decay of 190Pt to the first excited level of 186Os (Eexc = 137.2 keV) was observed for the first time., 4 pages, contribution to the MEDEX'13 Conference, corrected list of authors

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

Development of low radioactive technique allows to investigate many other rare nuclear and subnuclear processes: double [Formula: see text] decay, rare [Formula: see text] and [Formula: see text] decays, and to search for hypothetical particles and processes like axions, charge nonconserving decays, the nucleon, di-nucleon and tri-nucleon decays into invisible channels, to test the Pauli principle. Here, we present results of the rare processes searches and development of instrumentation for low counting experiments.

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

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

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.

Radiopure ZnWO 4 crystal scintillators with mass (0.1–0.7 kg) have been developed and put inmeasurement in the Gran Sasso National Laboratories of the INFN to search for rare processes. The radioactive contamination of the crystals have been estimated and the double beta decay of zinc and tungsten isotopes was searched for, reaching a sensitivity at the level of 10 18 −10 21 yr; in addition a new half-life limit on alpha transition of 183 W to the metastable excited level of 179 Hf has also been obtained. The achieved radiopurity of the ZnWO 4 crystals make them very promising detectors for ββ decay investigations while their anisotropic features make them very interesting detectors to investigate dark matter particles directionality.

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

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.