Search

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 .

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.

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.

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.

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.

beta decay of (113)Cd was studied with the help of a low background CdWO(4) crystal scintillator (mass of 434 g) in an experiment at the Gran Sasso National Laboratories of the INFN for a period of 2758 h. The shape of the spectrum of the non-unique fourth-forbidden decay of (113)Cd was measured, and the half-life of (113)Cd was determined as T(1/2)=(8.04 +/- 0.05)x10(15) yr.

The indication for the a decay of Eu-151 (Q alpha = 1.964 MeV) with the half-life T-1/2(alpha) = 5(-3)(+11) x 10(18) yr has been observed for the first time with the help of a low background CaF2(Eu) crystal scintillator (mass of 370 g) in measurement at the Gran Sasso National Laboratories of the INFN during 7426 h. In a conservative approach the lower limit on the half-life of Eu-151 has been established as T-1/2(alpha) >= 1.7 x 10(18) yr at 68% C.L. (c) 2007 Elsevier B.V. All rights reserved.

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.

An update on the activity for particle Dark Matter direct detection by liquid xenon target-detector is presented.