Search

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.

International audience; Low background scintillation setup has been developed that exhibits 3 orders of magnitude lower counting rate of a large volume (2.1 kg) CdWO4 detector in the energy region 0.5–2.6 MeV, and one order of magnitude above 3 MeV. The background reduction was achieved by application of radiopure passive shield, active plasticscintillation muon veto placed above the setup and pulse-shape discrimination. Construction of additional plastic scintillation counters is in progress to reduce the residual cosmic muons background. The setup can be applied to develop radiopure scintillators, measure radioactive contamination of materials, carry out small scale low counting experiments.

The first direct search for the double electron capture ($2\epsilon$) and the electron capture with positron emission ($\epsilon\beta^+$) in $^{144}$Sm to the ground state and to the excited levels of $^{144}$Nd was realized by measuring - over 1899 h - a 342 g sample of highly purified samarium oxide (Sm$_2$O$_3$) with the ultra-low background HP-Ge $\gamma$ spectrometer GeCris (465 cm$^3$) at the STELLA facility of the Gran Sasso National Laboratory (LNGS). No effect was observed and half-life limits were estimated at the level of $T_{1/2} \sim (0.1-1.3) \times 10^{20}$ yr (90% C.L.). Moreover, for the first time half-life limits of the double beta ($2\beta^-$) decay of $^{154}$Sm to several excited levels of $^{154}$Gd have been set; they are at the level of $T_{1/2} \sim (0.06-8) \times 10^{20}$ yr (90% C.L.)., Comment: 20 pages, 7 figures and 4 tables

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.

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 sample of 100MoO3 powder with molybdenum enriched in 100Mo to 99.5% and mass of 1199 g was measured for 18120 h in a low-background set-up with 4 HP Ge detectors ( ≃ 225 cm 3 volume each one) deep underground (3600 m w.e.) at the Laboratori Nazionali del Gran Sasso of the INFN (Italy). The two γ quanta of 540 keV and of 591 keV emitted in the deexcitation process after a 2 β 2 ν decay of 100Mo to the 0 1 + excited level of 100Ru ( E exc = 1131 keV ) are observed in the accumulated data both in coincidence and in the 1-dimensional sum spectrum. The measured half life is: T 1 / 2 = 6.9 − 0.8 + 1.0 ( stat. ) ± 0.7 ( syst. ) × 10 20 yr , well in agreement with positive results obtained in previous experiments. Moreover, the limit on charge non-conserving β decay of 100Mo is also set: τ CNC > 4.5 × 10 19 yr at 90% C.L.; it corresponds to the limit on CNC admixture in weak currents: ϵ ν 2 2.9 × 10 − 21 .

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.

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.

Energy resolution, light yield, non-proportionality in the scintillation response, alpha/beta ratio, pulse shape for gamma rays and alpha particles were studied with CdWO4 crystal scintillators. Some indication for a difference in the emission spectra for gamma rays and alpha particles was observed. No dependence of CdWO4 pulse shape on emission spectrum wavelengths under laser, alpha particles and gamma ray excitation was observed. Dependence of scintillation pulse shape for gamma quanta and alpha particles and pulse-shape discrimination ability on temperature was measured in the range of 0-24 degrees., Comment: 22 pages, 14 figures, submitted to NIMA

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.

The CARVEL (CAlcium Research for VEry Low neutrino mass) experiment to search for the double β decay of 48 Ca with the help of enriched 48 CaWO 4 crystal scintillators has been considered. Scintillation properties (energy resolution, α/β ratio, pulse-shape discrimination ability) and radiopurity of CaWO 4 scintillators were studied. Despite rather high radioactive contaminations, the background rate of the CaWO 4 detector in the energy region 3.6–5.4 MeV (energy window of the 48 Ca neutrinoless 2β decay) was reduced down to 0.07 counts/(yr keV kg). With ≈100 kg array of the 48 CaWO 4 crystals the sensitivity of the CARVEL experiment (in terms of the half-life limit for the 0ν2β decay) is estimated as T 1 / 2 0 ν > 10 27 yr. This value corresponds to the neutrino mass constraint m ν

The unique features (super-low background and large sensitive volume) of the CTF and BOREXINO set ups are used in the CAMEO project for a high sensitivity study of \(^{100}\)Mo and \(^{116}\)Cd neutrinoless 2\(\beta \) decay. Pilot measurements with \(^{116}\)Cd and Monte Carlo simulations show that the sensitivity of the CAMEO experiment (in terms of the half-life limit for \( 0\nu 2\beta \) decay) is \(\approx 4\times 10^{24}\) yr with a 1 kg source of \(^{100}\)Mo and \(\approx 10^{26}\) yr with \(\approx \)100 kg of enriched \( ^{116}\)CdWO\(_4\) crystals placed in the liquid scintillator of the CTF. The last value corresponds to a limit on the neutrino mass of \(m_\nu \leq 0.06\) eV. Similarly with 1000 kg of \(^{116}\)CdWO\(_4\) crystals located in the BOREXINO apparatus the neutrino mass limit can be pushed down to \(m_\nu \leq 0.02\) eV.

The unique features of the CTF and BOREXINO set ups are used for a high sensitivity study of 100 Mo and 116 Cd neutrinoless 2 β decay. Pilot measurements with 116 Cd and Monte Carlo simulation show that the sensitivity of the CAMEO experiment (in terms of the T 1/2 limit for 0 ν 2 β decay) is (3–5) ×10 24 yr with a 1 kg source of 100 Mo ( 116 Cd, 82 Se, 150 Nd) and ≈10 26 yr with 65 kg of 116 CdWO 4 crystals placed in the CTF. The last value corresponds to a limit on the neutrino mass of m ν ⩽0.06 eV. Moreover, with 1000 kg of 116 CdWO 4 crystals located in the BOREXINO apparatus the neutrino mass limit can be pushed down to m ν ⩽0.02 eV.

A new step of the 116Cd 2β-decay experiment is in progress at the Solotvina Underground Laboratory. The upgraded setup consists of four enriched 116CdWO4 crystal scintillators of total mass 339 g. As an active shield, 15 CdWO4 crystals (20.6 kg) are used. The background rate (in the energy interval 2.7–2.9 MeV) is 0.06 count/(yr kg keV), one order of magnitude lower than in the previous apparatus. Combined with results of preceding measurements, the half-life limit for the neutrinoless 2β decay of 116Cd to the ground state of 116Sn is determined as T1/2(0ν)≥5.1×1022 yr with 90% C.L. The limits on T1/2 for transitions to the excited 21+ and 01+ levels of 116Sn are 8.6×1021 and 4.1×1021 yr, respectively (at a 90% C.L.). For 0ν2β decay accompanied by the emission of one and two Majorons, the constraints on the half-life are T1/2(0νM1)≥1.4×1021 yr and T1/2 (0νM2)≥4.1×1020 yr (at a 90% C.L.). The corresponding constraints on the neutrino mass and the neutrino-Majoron coupling constant are 〈mv〉 ≤ 3.1 eV and 〈gM〉 ≤ 1.9 × 10−4, respectively.

Final results of the 2 β decay experiment, performed in the Solotvina Underground Laboratory with the help of low-background 116 CdWO 4 crystal scintillators, are presented. The revised half-life value of the two-neutrino 2 β decay of 116 Cd has been measured as T 1 / 2 2 ν = 2.9 −0.3 +0.4 × 10 19 yr, and the new half-life limit on the neutrinoless 2 β decay of 116 Cd has been established as T 1 / 2 0 ν ⩾ 1.7 (2.6)×10 23 yr at 90% (68%) C.L. The latter corresponds to a restriction on the Majorana neutrino mass: m ν ⩽ 1.7 (1.4) eV at 90% (68%) C.L. The CAMEO project could further advance sensitivity of the 116 Cd experiment to m ν ⩽ 0.05 eV.

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.

A low background scintillation detector with a CdWO4 crystal of 1.046 kg was used to search forβ + β + andβ +/EC processes in106Cd. For the neutrinoless mode the limits T1/2(0νβ + β +)≥2.2·1019 y and T1/2(0νβ +/EC)≥5.5·1019 y were obtained with 90% C.L. For the possible two neutrino decay limits of T1/2(2νβ + β +)≥9.2·1017 y and T1/2(2νβ +/EC)≥2.6·1017 y have been determined with 99% C.L.

A low background scintillation detector with a CdWO4 crystal of 1.046 kg was used to search for β+β+ and β+/EC processes in 106Cd. For the neutrinoless mode the limits T1/2(0νβ+β+) ≥ 2.2 · 1019 y and T1/2(0νβ+/EC) ≥ 5.5 · 1019 y were obtained with 90% C.L. For the possible two neutrino decay limits of T1/2(2νβ+β+) ≥ 9.2 · 1017 y and 1/2(2νβ+/EC) ≥ 2.6 · 1017 y have been determined with 99% C.L.

A low background scintillation spectrometer based on CdWO 4 crystals of large volume (100–200 cm 3 ) with improved energy resolution has been developed as a result of advances in crystal growth, optimization of light collection and design of a special electronic unit for amplification and shaping of the CdWO 4 signals. The energy resolution of crystals with volume 80–150 cm 3 is 10–12% for 662 keV γ-rays. A value of 7–8% at 662 keV, which is comparable to Nal(TI), has been obtained with small samples (10–20 cm 3 ). The high purity of the CdWO 4 crystals ( 228 Thcontamination is less than 8 μBq/kg, that of 226 Ra less than 13 μBq/kg) allows construction of unique spectrometers based on CdWO 4 crystals of large volume for environmental control, well logging and measurements of radioactive contamination in various samples with a sensitivity of 10 −12 to 2 × 10 −13 Ci/kg.

The experiment was performed at the Solotvina Underground Laboratory with CdWO4 crystal scintillators enriched in 116Cd to 83%. The total data collection time was about 30000 hours. Limits of T 1 2 0ν ≥2.9·10 22 y (90% CL) and T 1 2 2ν ≥1.8·10 19 y (99% CL) were obtained for 0ν2β and 2ν2β decay of 116Cd. After subtraction of the spectrum obtained with a natural CdWO4 scintillator a remaining yield was seen consistent with 2ν2β decay of 116Cd with T 1 2 2ν = {2.7 −0.4 +0.5 ( stat. ) −0.6 +0.9 ( syst. )}·10 19 . However, the imitation of the effect by impurities of 90Sr (at the level of 2·10−3 Bq/kg) cannot be excluded.

A search for double beta decay of 64,70Zn, 180,186W was carried out by using low background ZnWO4 crystal scintillators, while a CeCl3 scintillation detector was applied to investigate 2β processes in 136,138,142Ce. A search for 2β decay of 96,104Ru, 156,158Dy, 190,198Pt and study of 2ν2β decay of 100Mo to the first excited 0+ level of 100Ru were realized by ultra‐low background HPGe γ spectrometry. Moreover, CdWO4 crystal scintillators from enriched 106Cd and 116Cd isotopes were developed to search for 2β decay of 106Cd and 116Cd. Finally, experiments aimed to investigate 96,104Ru and 116Cd are in progress and a new phase of the experiment to search for 2β processes in 106Cd is in preparation.

An experiment to search for 2b processes in 106Cd with the help of 106CdWO4 crystal scintillator (mass of 215 g), enriched in 106Cd up to 66%, is in progress at the Gran Sasso National Laboratories of the INFN (Italy). After 1320 h of data taking, limits on double beta processes in 106Cd have been established on the level of 1019–1020 yr, in particular (all the results at 90% C.L.): T1/2(0ν2e)>3.6×1020 yr, T1/2(2νeβ+)>7.2×1019 yr, and T1/2(2ν2β+)>2.5×1020 yr. Resonant 0ν2e processes have been restricted as T1/2(0ν2K)>1.4×1020 yr and T1/2(0νLK)>3.2×1020 yr. A possible resonant enhancement of the 0ν2e processes is estimated in the framework of the QRPA approach.

An experiment looking for ss decay of 100 Mo to excited states of 100 Ru has been performed in the Frejus Underground Laboratory. The used set-up included a high purity Ge detector and 1 kg of 99.5% enriched 100 Mo. Half-life limits in the range 10 21 yr have been obtained.

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...

Radioactive contaminations of CaWO4, ZnWO4, CdWO4, and Gd2SiO5:Ce crystal scintillators were measured in the Solotvina Underground Laboratory. The Monte Carlo simulation of contributing radioactive sources, the time‐amplitude and pulse‐shape analyses of the experimental data were applied. CaWO4 and GSO scintillators are considerably polluted by uranium and thorium, while the total α activity in ZnWO4 and CdWO4 scintillators does not exceed the level of a few mBq/kg. Particular radioactivity was observed in CaWO4 (α active 180W), CdWO4 (β active 113Cd, 2v2β decay of 116Cd, 180W), and GSO (α active 152Gd) detectors. The radioactive contamination of the studied scintillation crystals is compared with that of commonly used detectors.

The experiment with a large (≈95 cm3) Gd2SiO5:Ce crystal scintillator has been performed in the Solotvina Underground Laboratory to search for neutrinoless double beta decay of 160Gd. The background rate was reduced to a level of 0.045 counts/h/keV/kg in the vicinity of ββ decay energy of 160Gd (1730 keV). The half-life limits have been set for 0vββ decay of 160Gd: T1/2ov(g.s. → g.s.) ≥ 8.2·1020 y (90% CL); T1/2ov (0+ → 2+) ≥ 8.2·1020 y (90% CL).

The experiment was performed at the Solotvina Underground Laboratory with CdWO 4 crystal scintillators enriched in 116 Cd to 83%. For the total data collection time about 12000 hours the limit of half-life T 1/2 ov ≥ 3.2·10 22 y (90% CL) was obtained for 0vββ decay of 116 Cd which corresponds to the restriction of the neutrino mass less than 3.9 eV.

Final results of the double $\ensuremath{\beta}$ decay experiment, performed with the help of low background ${}^{116}{\mathrm{CdWO}}_{4}$ crystal scintillators in the Solotvina Underground Laboratory, are presented. In particular, the revised half-life value of the two-neutrino 2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ has been measured as ${T}_{1/2}^{2\ensuremath{\nu}}{=2.9}_{\ensuremath{-}0.3}^{+0.4}\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{yr},$ and the new half-life limit on the neutrinoless $2\ensuremath{\beta}$ decay of ${}^{116}\mathrm{Cd}$ has been established as ${T}_{1/2}^{0\ensuremath{\nu}}g~1.7(2.6)\ifmmode\times\else\texttimes\fi{}{10}^{23}\mathrm{yr}$ at 90% (68%) C.L. The latter corresponds to a restriction on the neutrino mass: ${m}_{\ensuremath{\nu}}l~1.7(1.4)\mathrm{eV}$ at 90% (68%) C.L. Besides, new ${T}_{1/2}$ bounds (at the level of ${10}^{17}\char21{}{10}^{21}\mathrm{yr})$ were set for various $2\ensuremath{\beta}$ processes in ${}^{106}\mathrm{Cd},$ ${}^{108}\mathrm{Cd},$ ${}^{114}\mathrm{Cd},$ ${}^{180}\mathrm{W},$ and ${}^{186}\mathrm{W}$ nuclei.

A new phase of a ${}^{116}\mathrm{Cd}$ double \ensuremath{\beta} decay experiment is in progress in the Solotvina Underground Laboratory. Four enriched ${}^{116}{\mathrm{CdWO}}_{4}$ scintillators with total mass of 339 g are used in a setup, whose active shield is made of 15 natural ${\mathrm{CdWO}}_{4}$ crystals (20.6 kg). The background rate in the energy interval 2.5--3.2 MeV is 0.03 counts/yr kg keV. The half-life for 2\ensuremath{\nu}2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ is measured as ${T}_{1/2}(2\ensuremath{\nu})=2.6\ifmmode\pm\else\textpm\fi{}0.1(\mathrm{stat}{)}_{\ensuremath{-}0.4}^{+0.7}(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{19}$ yr. The ${T}_{1/2}$ limits for neutrinoless 2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ are set at ${T}_{1/2}g~0.7(2.5)\ifmmode\times\else\texttimes\fi{}{10}^{23}$ yr at 90%(68%) C.L. for transition to ground state of ${}^{116}\mathrm{Sn},$ while for decays to the first ${2}_{1}^{+}$ and second ${0}_{1}^{+}$ excited levels of ${}^{116}\mathrm{Sn}$ at ${T}_{1/2}g~1.3(4.8)\ifmmode\times\else\texttimes\fi{}{10}^{22}$ yr and $g~0.7(2.4)\ifmmode\times\else\texttimes\fi{}{10}^{22}$ yr with 90%(68%) C.L., respectively. For 0\ensuremath{\nu}2\ensuremath{\beta} decay with emission of one or two Majorons, the limits are ${T}_{1/2}(0\ensuremath{\nu}M1)g~3.7(5.8)\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr and ${T}_{1/2}(0\ensuremath{\nu}M2)g~5.9(9.4)\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr at 90%(68%) C.L. Restrictions on the value of the neutrino mass, right-handed admixtures in the weak interaction, and the neutrino-Majoron coupling constant are derived as ${m}_{\ensuremath{\nu}}l~2.6(1.4)$ eV, $\ensuremath{\eta}l~3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8},$ $\ensuremath{\lambda}l~3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6},$ and ${g}_{M}l~12(9.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ at 90%(68%) C.L., respectively.

The 2β decay experiment (about 30000 h) with 116CdWO4 scintillators enriched in 116Cd to 83% has been performed in the Solotvina Underground Laboratory. The limits T0ν1/2≥2.9⋅1022y (90% CL) and T2ν1/2≥1.8⋅1019y(99% CL) have been set for 0ν2β and 2ν2β decay of 116Cd. After substraction of the spectrum of natural CdWO4 scintillator from the spectrum of enriched 116CdWO4 detector the positive effect has been seen which is in accordance with 2ν2β decay of 116Cd with T2ν1/2= {2.70.5−0.4(stat.)+0.9−0.6(syst.)}⋅1019y. However the imitation of the effect by the impurities of 90Sr cannot be excluded.

Sample of 100MoO3 with molybdenum enriched in 100Mo to 99.5% and mass of 1199 g was measured deep underground (3600 m w.e.) in the Laboratori Nazionali del Gran Sasso of INFN, Italy; during 17249 h with a low-background set-up with 4 HP Ge detectors. After 2β2ν decay of 100Mo to the 0+1 excited level of 100Ru (Eexc = 1131 keV), two γ quanta of 540 keV and 591 keV should be emitted in deexcitation process. Both these γ's are observed in the accumulated data as in coincidence spectrum as well in 1-dimensional sum spectrum. Measured half life is T1/2 = (7.0+1.1−0.8) × 1020 yr, in agreement with positive results obtained in previous experiments.

Measurements of 116 Cd double beta decay with help of enriched 116 CdWO 4 crystal scintillator are in progress in the Solotvina Underground Laboratory. The last part of the exposition with the background rate less than 0.6 counts/y·kg·keV (in the region of interest 2.7–2.9 MeV) is about 19000 hours. The half-life limit T 1 2 (0ν)≥3.2·10 22 y (90% C.L.) is obtained for neutrinoless 2β decay of 116 Cd. It corresponds to restrictions on the values of the neutrino mass 〈m ν 〉≤3.9 eV, right-handed admixtures in weak interaction 〈η〉≤5.7·10 −8 , 〈λ〉5.0·10 −6 and R-parity violating parameter of minimal supersymmetric standard model e≤1.1·10 −3 . For neutrinoless modes with emission of one and two Majorons, the limits T 1 2 (0ν M 1)≥1.2·10 21 y and T 1 2 (0ν M 2)≥2.4·10 20 y (90% C.L.) are determined. To advance these results to a level of the limit ťm ν 〉≤1–2 eV, the improved set-up with four enriched 116 CdWO 4 crystals is in mounting low.

Measuremennts of 116Cd double beta decay with the help of enriched 116CdWO4 crystal scintillators are in progress in the Solotvina Underground Laboratory. The last part of the exposition with the background rate 0.7 counts/y·kg·keV (in the region of 116Cd 0ν2β decay 2.7–2.9 MeV) is 22826 hours. For neutrinoless modes with emission of one and two Majorons, the limits T 1 2 (0ν M1 ) ⩾ 1.2 × 10 21 y and T 1 2 (0ν M2 ) ⩾ 2.6 × 10 20 y (90% C.L.) are determined. The above mentioned values give the restriction on the Majoron-neutrino coupling constant of gM ⩽ 2.1 × 10−4. To improve these results, an advanced set-up with four enriched 116CdWO4 detectors shielded by fifteen large (1.5–2 kg) CdWO4 crystals has been mounted.