Pulse-shape discrimination with PbWO4_4 crystal scintillators

The light output, $\alpha/\beta$ ratio, and pulse shape have been investigated at $-25^\circ$ C with PbWO$_4$ crystal scintillators undoped, and doped by F, Eu, Mo, Gd and S. The fast $0.01-0.06 \mu$s and middle $0.1-0.5 \mu$s components of scintillation decay were observed for all the samples. Slow components of scintillation signal with the decay times $1-3 \mu$s and $13-28 \mu$s with the total intensity up to $\approx50$ have been recognized for several samples doped by Molybdenum. We found some indications of a pulse-shape discrimination between $\alpha$ particles and $\gamma$ quanta with PbWO$_4$ (Mo doped) crystal scintillators.Comment: 12 pages, 5 figures, submitted to NIM

Search for 2β processes in 64Zn with the help of ZnWO4 crystal scintillator

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Search for double beta decay of Zinc and Tungsten with the help of low-background ZnWO4 crystal scintillators

Double beta processes in 64-Zn, 70-Zn, 180-W, and 186-W 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. Total time of measurements exceeds 10 thousands hours. New improved half-life limits on double electron capture and electron capture with positron emission in 64-Zn have been set, in particular (all the limits are at 90% C.L.): T1/2(0nu2EC)> 1.1e20 yr, T1/2(2nuECbeta+)>7.0e20 yr, and T1/2(0nuECbeta+)>4.3e20 yr. The different modes of double beta processes in 70-Zn, 180-W, and 186-W have been restricted at the level of 1e17-1e20 yr.Comment: 20 p., submitted to Phys. Rev.

Complete event-by-event α/γ(β) separation in a full-size TeO2 CUORE bolometer by simultaneous heat and light detection

The CUORE project began recently a search for neutrinoless double-beta decay ($0\nu\beta\beta$) of $^{130}$Te with a $\mathcal{O}$(1 ton) TeO$_2$ bolometer array. In this experiment, the background suppression relies essentially on passive shielding, material radiopurity and anti-coincidences. The lack of particle identification in CUORE makes $\alpha$ decays at the detector surface the dominant background, at the level of $\sim$0.01 counts/(keV kg y) in the region of interest ($Q$-value of $0\nu\beta\beta$ of the order of 2.5 MeV). In the present work we demonstrate, for the first time with a CUORE-size (5$\times$5$\times$5 cm) TeO$_2$ bolometer and using the same technology as CUORE for the readout of the bolometric signals, an efficient $\alpha$ particle discrimination (99.9\%) with a high acceptance of the $0\nu\beta\beta$ signal (about 96\%). This unprecedented result was possible thanks to the superior performance (10 eV RMS baseline noise) of a Neganov-Luke-assisted germanium bolometer used to detect a tiny (70 eV) light signal dominated by $\gamma$($\beta$)-induced Cherenkov radiation in the TeO$_2$ detector. The obtained results represent a major breakthrough towards the TeO$_2$-based version of CUPID, a ton-scale cryogenic $0\nu\beta\beta$ experiment proposed as a follow-up to CUORE with particle identification

Scintillating bolometers based on ZnMoO4 and Zn100MoO4 crystals to search for 0ν2β decay of 100Mo (LUMINEU project): first tests at the Modane Underground Laboratory

The technology of scintillating bolometers based on zinc molybdate (ZnMoO4) crystals is under development within the LUMINEU project to search for decay of 100Mo with the goal to set the basis for large scale experiments capable to explore the inverted hierarchy region of the neutrino mass pattern. Advanced ZnMoO4 crystal scintillators with mass of ∼0.3 kg were developed and Zn100MoO4 crystal from enriched 100Mo was produced for the first time by using the low-thermal-gradient Czochralski technique. One ZnMoO4 scintillator and two samples (59 g and 63 g) cut from the enriched boule were tested aboveground at milli-Kelvin temperature as scintillating bolometers showing a high detection performance. The first results of the low background measurements with three ZnMoO4 and two enriched detectors installed in the EDELWEISS set-up at the Modane Underground Laboratory (France) are presented

100^{100}Mo-enriched Li2_2MoO4_4 scintillating bolometers for 0ν2β0\nu 2\beta decay search: From LUMINEU to CUPID-0/Mo projects

International audienceA scintillating bolometer technology based on 100Mo-enriched lithium molybdate (Li2100MoO4) crystals has been developed by LUMINEU to search for neutrinoless double-beta (0ν2β) decay of 100Mo. The results of several low temperature tests at underground environments have proved the reproducibility of high detector performance and crystal radiopurity: in particular ∼5–6 keV FWHM energy resolution and at least 9σ rejection of α’s in the vicinity of the 0ν2β decay of 100Mo (3034 keV) and below 10 µBq/kg bulk activity of 228Th and 226Ra. A modest acquired exposure (0.1 kg×yr) is a limiting factor of the LUMINEU experiment sensitivity to the 0ν2β decay half-life of 100Mo (T1/2 ≥ 0.7×1023 yr at 90% C.L.), however the two-neutrino 2β decay has been measured with the best up to-date accuracy, T1/2 = [6.92 ± 0.06(stat.) ± 0.36(syst.)l × 1018 yr. The applicability of the LUMINEU technology for a tonne-scale 0ν2β decay bolometric project CUPID is going to be demonstrated by the CUPID-0/Mo experiment with ∼5 kg of 100Mo embedded in forty 0.2 kg Li2100MoO4 scintillating bolometers. A first phase of the experiment with twenty Li2100MoO4 detectors is in preparation at the Modane underground laboratory (France) to start by the end of 2017

Search for naturally occurring seaborgium with radiopure 116^{116}CdWO4_{4} crystal scintillators

International audienceA detector containing two radiopure $^{116}$CdWO$_{4}$ crystal scintillators with total mass of 1.2 kg was operated during 35324 h at the Gran Sasso Underground Laboratory (INFN, Italy) with the main aim to investigate double beta decay of $^{116}$Cd. As a by-product of the experiment, a new upper limit on atomic abundance of hypothetical naturally occurring long-lived seaborgium (eka-tungsten, Z = 106) in tungsten was set at 5.1 10$^{−15}$ atom(Sg)/atom(W) with 90% C.L. (assuming the Sg half-life of 10$^{9}$ yr) by the analysis of the alpha decay events. This limit is better than those obtained with a ZnWO$_{4}$ scintillator and in other types of experiments which used the accelerator mass spectrometry or searched for spontaneous fission of superheavy elements

Search for rare processes with ZnWO

Radiopure ZnWO4 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 1018−1021 yr; in addition a new half-life limit on alpha transition of 183W to the metastable excited level of 179Hf has also been obtained. The achieved radiopurity of the ZnWO4 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

Charge-to-heat transducers exploiting the Neganov-Trofimov-Luke effect for light detection in rare-event searches

International audienceIn this work we present how to fabricate large-area (15 cm 2 ), ultra-low threshold germanium bolometric photo-detectors and how to operate them to detect few (optical) photons. These detectors work at temperatures as low as few tens of mK and exploit the Neganov-Trofimov-Luke (NTL) effect. They are operated as charge-to-heat transducers: the heat signal is linearly increased by simply changing a voltage bias applied to special metal electrodes, fabricated onto the germanium absorber, and read by a (NTD-Ge) thermal sensor. We fabricated a batch of five prototypes and ran them in different facilities with dilution refrigerators. We carefully studied how impinging spurious infrared radiation impacts the detector performances, by shining infrared photons via optical-fiber-guided LED signals, in a controlled manner, into the bolometers. We hence demonstrated how the radiation-tightness of the test environment tremendously enhances the detector performances, allowing to set electrode voltage bias up to 90 volts without any leakage current and signal-to-noise gain as large as a factor 12 (for visible photons). As consequence, for the first time we could operate large-area NTD-Ge-sensor-equipped NTL bolometric photo-detectors capable to reach sub 10-eV baseline noise (RMS). Such detectors open new frontiers for rare-event search experiments based on low light yield Ge-NTD equipped scintillating bolometers, such the CUPID neutrinoless double-beta decay experiment

Search for alpha and double alpha decays of natural Nd isotopes accompanied by gamma quanta

International audienceFrom 7 naturally occurring Nd isotopes, 5 are unstable in relation to α decay. If an excited level of the daughter nucleus is populated, or the daughter nucleus is unstable, γ quanta can be emitted. We used an ultra-low background spectrometry system with 4 high purity germanium (HPGe) detectors (about 225 cm$^{3}$ volume each) to search for such decays using a highly purified Nd-containing sample with mass of 2.381 kg. Measurements were performed at the INFN Gran Sasso underground laboratory (with an overburden of about 3600 m w.e.) during 51,237 h. Half-life limits for α decays of $^{143}$Nd and $^{145}$Nd were determined to be T$_{1/2}$($^{143}$Nd) > 1.1 × 10$^{20}$ year and T$_{1/2}$($^{145}$Nd) > 2.7 × 10$^{19}$ year at 90% C.L. This is an increase of three and two orders of magnitude, respectively, compared with the most restrictive values currently given in literature. A limit for α decay of $^{144}$Nd to the excited level of $^{140}$Ce with E$_{exc}$ = 1596.2 keV was determined for the first time as T$_{1/2}$($^{144}$Nd → $^{140}$Ce$^{*}$) > 9.3 × 10$^{20}$ year. Restriction for the α decay of $^{146}$Nd to the excited level of $^{142}$Ce with E$_{exc}$ = 641.3 keV was increased by 3 orders of magnitude to T$_{1/2}$($^{146}$Nd → $^{142}$Ce$^{*}$) > 1.4 × 10$^{21}$ year. For α and 2α decays of $^{148}$Nd, first T$_{1/2}$ limits were set as 4.2 × 10$^{18}$ year and 2.1 × 10$^{20}$ year, respectively