Radioactive contamination of ZnWO4 crystal scintillators

The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed.Comment: 15 pages, 8 figures, 6 tables, submitted for publicatio

Radioactive contamination of SrI2(Eu) crystal scintillator

A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using the Stockbarger growth technique. The crystal was subjected to a characterization that includes relative photoelectron output and energy resolution for gamma quanta. The intrinsic radioactivity of the SrI2(Eu) crystal scintillator was tested both by using it as scintillator at sea level and by ultra-low background HPGe gamma spectrometry deep underground. The response of the SrI2(Eu) detector to alpha particles (alpha/beta ratio and pulse shape) was estimated by analysing the 226Ra internal trace contamination of the crystal. We have measured: alpha/beta=0.55 at E_alpha=7.7 MeV, and no difference in the time decay of the scintillation pulses induced by alpha particles and gamma quanta. The application of the obtained results in the search for the double electron capture and electron capture with positron emission in 84Sr has been investigated at a level of sensitivity: T_1/2 \sim 10^{15}-10^{16} yr. The results of these studies demonstrate the potentiality of this material for a variety of scintillation applications, including low-level counting experiments.Comment: 24 pages, 12 figures, 4 tables, accepted for publication on Nucl. Instrum. Meth.

Search for double beta decay processes in 106Cd with the help of 106CdWO4 crystal scintillator

A search for the double beta processes in 106Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) with the help of a 106CdWO4 crystal scintillator (215 g) enriched in 106Cd up to 66%. After 6590 h of data taking, new improved half-life limits on the double beta processes in 106Cd were established at the level of 10^{19}-10^{21} yr; in particular, T_{1/2}(2\nu \epsilon \beta^+) > 2.1 10^{20} yr, T_{1/2}(2\nu 2\beta^+) > 4.3 10^{20} yr, and T_{1/2}(0\nu 2\epsilon) > 1.0 10^{21} yr. The resonant neutrinoless double electron captures to the 2718 keV, 2741 keV and 2748 keV excited states of 106Pd are restricted to T_{1/2}(0\nu 2K) > 4.3 10^{20} yr, T_{1/2}(0\nu KL1) > 9.5 10^{20} yr and T_{1/2}(0\nu KL3) > 4.3 10^{20} yr, respectively (all limits at 90% C.L.). A possible resonant enhancement of the 0\nu 2\epsilon processes is estimated in the framework of the QRPA approach. The radioactive contamination of the 106CdWO4 crystal scintillator is reported.Comment: Minor changes of half-life limits after improving the data analysis; version accepted for publication on Phys. Rev.

Searches for neutrinoless resonant double electron captures at LNGS

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 Conferenc

Low background detector with enriched 116CdWO4 crystal scintillators to search for double beta decay of 116Cd

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 Instrumentatio

Dark Matter Search Results from the PICO-60C(3)F(8) Bubble Chamber

[EN] New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C3F8 located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C3F8 exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than one event per month. A blind analysis of an efficiency-corrected 1167-kg day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the weakly interacting massive particle (WIMP)-proton spin-dependent cross section at 3.4 x 10(-41) cm(2) for a 30-GeVc(-2) WIMP, more than 1 order of magnitude improvement from previous PICO results.The PICO Collaboration wishes to thank SNOLAB and its staff for support through underground space, logistical, and technical services. SNOLAB operations are supported by the Canada Foundation for Innovation and the Province of Ontario Ministry of Research and Innovation, with underground access provided by Vale at the Creighton mine site. We are grateful to Kristian Hahn and Stanislava Sevova of Northwestern University and Bjorn Penning of the University of Bristol for their assistance and useful discussion. We wish to acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI) for funding. We acknowledge the support from National Science Foundation (NSF) (Grants No. 0919526, No. 1506337, No. 1242637, and No. 1205987). We acknowledge that this work is supported by the U.S. Department of Energy (DOE) Office of Science, Office of High Energy Physics (under Award No. DE-SC-0012161), by a DOE Office of Science Graduate Student Research (SCGSR) award, by Direccion General Asuntos del Personal Academico, Universidad Nacional Autonoma de Mexico (DGAPA-UNAM) through the grant Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT) No. IA100316 and by Consejo Nacional de Ciencia y Tecnologia (CONACyT) (Mexico) through Grant No. 252167, by the Department of Atomic Energy (DAE), the Government of India, under the Center of AstroParticle Physics II project (CAPP-II) at Saha Institute of Nuclear Physics (SINP), by the Czech Ministry of Education, Youth and Sports (Grant No. LM2015072), and by the Spanish Ministerio de Economia y Competitividad, Consolider MultiDark (Grant No. CSD2009-00064). This work is partially supported by the Kavli Institute for Cosmological Physics at the University of Chicago through NSF Grant No. 1125897, and an endowment from the Kavli Foundation and its founder Fred Kavli. We also wish to acknowledge the support from Fermi National Accelerator Laboratory under Contract No. De-AC02-07CH11359, and Pacific Northwest National Laboratory, which is operated by Battelle for the U.S. Department of Energy under Contract No. DE-AC05-76RL01830. We also thank Compute Canada and the Center for Advanced Computing, ACENET, Calcul Quebec, Compute Ontario, and WestGrid for the computational support.Amole, C.; Ardid Ramírez, M.; Arnquist, I.; Asner, DM.; Baxter, D.; Behnke, E.; Bhattacharjee, P.... (2017). Dark Matter Search Results from the PICO-60C(3)F(8) Bubble Chamber. Physical Review Letters. 118(25). https://doi.org/10.1103/PhysRevLett.118.251301S11825Olive, K. A. (2014). Review of Particle Physics. 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Search for new phenomena in final states with an energetic jet and large missing transverse momentum inppcollisions ats=13  TeVusing the ATLAS detector. Physical Review D, 94(3). doi:10.1103/physrevd.94.03200