868 research outputs found

    Rejection of randomly coinciding events in ZnMoO4_4 scintillating bolometers

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    Random coincidence of events (particularly from two neutrino double beta decay) could be one of the main sources of background in the search for neutrinoless double beta decay with cryogenic bolometers due to their poor time resolution. Pulse-shape discrimination by using front edge analysis, mean-time and χ2\chi^2 methods was applied to discriminate randomly coinciding events in ZnMoO4_4 cryogenic scintillating bolometers. These events can be effectively rejected at the level of 99% by the analysis of the heat signals with rise-time of about 14 ms and signal-to-noise ratio of 900, and at the level of 92% by the analysis of the light signals with rise-time of about 3 ms and signal-to-noise ratio of 30, under the requirement to detect 95% of single events. These rejection efficiencies are compatible with extremely low background levels in the region of interest of neutrinoless double beta decay of 100^{100}Mo for enriched ZnMoO4_4 detectors, of the order of 10410^{-4} counts/(y keV kg). Pulse-shape parameters have been chosen on the basis of the performance of a real massive ZnMoO4_4 scintillating bolometer. Importance of the signal-to-noise ratio, correct finding of the signal start and choice of an appropriate sampling frequency are discussed

    Rejection of randomly coinciding events in Li2_2100^{100}MoO4_4 scintillating bolometers using light detectors based on the Neganov-Luke effect

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    Random coincidences of nuclear events can be one of the main background sources in low-temperature calorimetric experiments looking for neutrinoless double-beta decay, especially in those searches based on scintillating bolometers embedding the promising double-beta candidate 100^{100}Mo, because of the relatively short half-life of the two-neutrino double-beta decay of this nucleus. We show in this work that randomly coinciding events of the two-neutrino double decay of 100^{100}Mo in enriched Li2_2100^{100}MoO4_4 detectors can be effectively discriminated by pulse-shape analysis in the light channel if the scintillating bolometer is provided with a Neganov-Luke light detector, which can improve the signal-to-noise ratio by a large factor, assumed here at the level of 750\sim 750 on the basis of preliminary experimental results obtained with these devices. The achieved pile-up rejection efficiency results in a very low contribution, of the order of 6×105\sim 6\times10^{-5} counts/(keV\cdotkg\cdoty), to the background counting rate in the region of interest for a large volume (90\sim 90 cm3^3) Li2_2100^{100}MoO4_4 detector. This background level is very encouraging in view of a possible use of the Li2_2100^{100}MoO4_4 solution for a bolometric tonne-scale next-generation experiment as that proposed in the CUPID project

    Final results of an experiment to search for 2beta processes in zinc and tungsten with the help of radiopure ZnWO4 crystal scintillators

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    A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO4 crystal scintillators (0.1-0.7 kg) at the Gran Sasso National Laboratories of the INFN. The total exposure of the low background measurements is 0.529 kg yr. New improved half-life limits on the double beta decay modes of 64Zn, 70Zn, 180W, and 186W have been established at the level of 10^{18}-10^{21} yr. In particular, limits on double electron capture and electron capture with positron emission in 64Zn have been set: T_{1/2}(2\nu 2K) > 1.1 10^{19} yr, T_{1/2} (0\nu 2\epsilon) > 3.2 10^{20} yr, T_{1/2} (2\nu \epsilon \beta^+) > 9.4 10^{20} yr, and T_{1/2} (0\nu \epsilon \beta^+) > 8.5 10^{20} yr, all at 90% C.L. Resonant neutrinoless double electron capture in 180W has been restricted on the level of T_{1/2} (0\nu 2\epsilon) > 1.3 10^{18} yr. A new half-life limit on alpha transition of 183W to the metastable excited level 1/2^- 375 keV of 179Hf has been established: T_{1/2} > 6.7 10^{20} yr.Comment: This is an author-created, un-copyedited version of an article published in J. Phys. G: Nucl. Part. Phys. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at doi: 10.1088/0954-3899/38/11/11510

    On the possibility to search for double beta decay of initially unstable (alpha/beta radioactive) nuclei

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    Possibilities to search for double beta decay of alpha/beta unstable nuclei, many of which have higher energy release than "conventional" (beta stable) double beta decay candidates, are discussed. First experimental half-life limits on double beta decay of radioactive nuclides from U and Th families (trace contaminants of the CaWO_4, CdWO_4 and Gd_2SiO_5 scintillators) were established by reanalyzing the data of low-background measurements in the Solotvina Underground Laboratory with these detectors (1734 h with CaWO_4, 13316 h with CdWO_4, and 13949 h with Gd_2SiO_5 crystals).Comment: 15 pages, 6 figure

    Investigation of rare nuclear decays with BaF2_2 crystal scintillator contaminated by radium

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    The radioactive contamination of a BaF2_2 scintillation crystal with mass of 1.714 kg was measured over 101 hours in the 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^{212}Po (present in the crystal scintillator due to contamination by radium) was measured as T1/2(212T_{1/2}(^{212}Po) = 298.8±\pm0.8(stat.)±\pm1.4(syst.) ns by analysis of the events' pulse profiles. The 222^{222}Rn nuclide is known as 100% decaying via emission of α\alpha particle with T1/2T_{1/2} = 3.82 d; however, its β\beta decay is also energetically allowed with Qβ=24±21Q_\beta = 24\pm21 keV. Search for decay chains of events with specific pulse shapes characteristic for α\alpha or for β/γ\beta/\gamma signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of 222^{222}Rn relatively to β\beta decay as Bβ<0.13B_\beta < 0.13% at 90% C.L. (equivalent to limit on partial half-life T1/2β>8.0T_{1/2}^\beta > 8.0 y). Half-life limits of 212^{212}Pb, 222^{222}Rn and 226^{226}Ra relatively to 2β2\beta decays are also improved in comparison with the earlier results.Comment: 10 pages, 9 figures, 2 table

    The event generator DECAY4 for simulation of double beta processes and decay of radioactive nuclei

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    The computer code DECAY4 is developed to generate initial energy, time and angular distributions of particles emitted in radioactive decays of nuclides and nuclear (atomic) deexcitations. Data for description of nuclear and atomic decay schemes are taken from the ENSDF and EADL database libraries. The examples of use of the DECAY4 code in several underground experiments are described.Comment: 8 pages, 1 fi

    Search for long-lived superheavy eka-tungsten with radiopure ZnWO4_4 crystal scintillator

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    The data collected with a radioactively pure ZnWO4_4 crystal scintillator (699 g) in low background measurements during 2130 h at the underground (3600 m w.e.) Laboratori Nazionali del Gran Sasso (INFN, Italy) were used to set a limit on possible concentration of superheavy eka-W (seaborgium Sg, Z = 106) in the crystal. Assuming that one of the daughters in a chain of decays of the initial Sg nucleus decays with emission of high energy α\alpha particle (Qα>8Q_\alpha > 8 MeV) and analyzing the high energy part of the measured α\alpha spectrum, the limit N(Sg)/N(W) < 5.5 ×\times 1014^{-14} atoms/atom at 90% C.L. was obtained (for Sg half-life of 109^9 yr). In addition, a limit on the concentration of eka-Bi was set by analysing the data collected with a large BGO scintillation bolometer in an experiment performed by another group [L. Cardani et al., JINST 7 (2012) P10022]: N(eka-Bi)/N(Bi) < 1.1 ×\times 1013^{-13} atoms/atom with 90% C.L. Both the limits are comparable with those obtained in recent experiments which instead look for spontaneous fission of superheavy elements or use the accelerator mass spectrometry.Comment: 9 pages, 2 figures; in press on Physica Script

    Search for double beta decay of 136^{136}Ce and 138^{138}Ce with HPGe gamma detector

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    Search for double β\beta decay of 136^{136}Ce and 138^{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 γ\gamma detector with a volume of 465 cm3^3 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 limT1/210171018\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.
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