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Double beta decay searches with enriched and scintillating bolometers

- Milano - Bicocca. Double beta decay searches with enriched and scintillating bolometers. Stefano Pirro. The Future of Neutrino Mass Measurements - NuMass 2010 INT Seattle February 8-11, 2010. . . . Background Issues (1). X. X. Internal trace contaminations ( 238 U and 232 Th).

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Double beta decay searches with enriched and scintillating bolometers

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  1. - Milano - Bicocca Double beta decay searches with enriched and scintillating bolometers Stefano Pirro The Future of Neutrino Mass Measurements - NuMass 2010 INT Seattle February 8-11, 2010 Stefano Pirro – NuMass 2010

  2.   Background Issues (1) Stefano Pirro – NuMass 2010

  3. X X Internal trace contaminations (238U and 232Th) Surrounding trace contaminations (238U and 232Th) Surface  contaminations Neutron induced background: direct and through (n,n’) 106Ru 106Rh (Q=3.5 MeV) (Fission) Long living - Emitters 110mAg (Q=2.9 MeV) (fast n activation) Background Issues (2) Stefano Pirro – NuMass 2010

  4. -region -region 76Ge 116Cd 130Te 100Mo 82Se 136 Xe CUORICINO  Background Environmental “underground” Background: 238U and 232Th trace contaminations Surface and Bulk contaminations Furthermore a not negligible part of the background can arise from high energy neutrons from -spallation Stefano Pirro – NuMass 2010

  5. Some History The first measurement of light and heat in a bolometer was performed in 1992 by the Milano group But this technique, using a silicon PD at low temperatures showed several difficulties • Radioactivity induced by the PD itself • Cold stage charge preamplifier inside the cryostat • Relatively small surface area of the PD For these reasons the technique was abandoned In 2004 we started to develop bolometer as LD (as CRESST and Rosebud Experiments) The activity was then funded by INFN through the BoLux (R&D) Experiment* 2007-2009 and by EC The CUPIDO R&D* project (INFN) funded for 2010 will go on with R&D on this technique. * Responsible: Stefano Pirro Stefano Pirro – NuMass 2010

  6. =C/G T=E/C Principles of operation Stefano Pirro – NuMass 2010

  7. Ge (Ø = 66 mm) FWHM=550 eV • Ge (Ø = 35 mm) FWHM=250 eV Light Detectors - Performances Our Light detectors are generally Pure Germanium disks (thickness 0.3-1 mm) . The Performances of a LD are normally evaluated through the Energy resolution on the 55Fe doublet (5.9 & 6.5 keV X-Ray) Stefano Pirro – NuMass 2010

  8. PbMoO4 ZnSe ZrO2 MgMoO4 CdMoO4 Li2MoO4 TeO2 SrMoO4 CdWO4 CaF2 CaMoO4 ZnMoO4 Summary of (almost) all the measured crystals Good Scintillation light Poor Scintillation light No Scintillation light Stefano Pirro – NuMass 2010

  9. Undoped48CaF2 In 2007 we tested a CaF2 crystal. The light output was “rather poor” but definitively enough to discriminate alpha’s Calibration (232Th) on a 3x3x3 cm3 PURE CaF2 crystal There was a lack of an actual calibration due to the “lightness” of the compound; nevertheless the Signal/noise ratio of the CaF2 was excellent. Stefano Pirro – NuMass 2010

  10. 4 3x3x3 cm3 (215 g each) CdWO4 1 common LD facing the 4 crystals CdWO4 – 3x3x6 Results on the first array of 116CdWO4 crystals (1) Stefano Pirro – NuMass 2010

  11. Background-Free area 2615 keV 208Tl  Results on the first array of 116CdWO4 crystals (2) The data on the single 420 g 3x3x6 cm3 crystal is presented here. The obtained scatter plot is shown it corresponds to 1066 hours of background measurement 44 days background The MC simulation predicts a background level of 10-4 c/keV/kg/y in the region of interest Stefano Pirro – NuMass 2010

  12. 226Ra, 222Rn, 218Po, 214Bi-214Po (56 mBq/kg) 210Pb (360 mBq/kg) Zn100MoO4 –A promising Molibdate A 22 g ZnMoO4 crystal was grown by Institute for Scintillation Materials (Kharkov, Ukraine) In collaboration with by Institute for Nuclear Research (Kiev, Ukraine) Stefano Pirro – NuMass 2010

  13. Ionizing particles / Ln (Light) Zn82Se –an extremely Puzzling compound (1) Looking at the coincidences between Heat in ZnSe and “Light” in the light detector, three population appears Stefano Pirro – NuMass 2010

  14. 337 g “new” ZnSe Crystal / Betaregion  Calibration with 232Th and a smeared  source Light Zn82Se –an extremely promising compound (2) First Results on a 4 cm  5 cm height 337 g ZnSe Crystal 210Po Smeared  source Rejection > 99.5 % Stefano Pirro – NuMass 2010

  15. It would be nice to obtain the same w/o this effort… “Beyond” Scintillating bolometers Scintillating bolometers are extremely powerful in order to discriminate background. Nevertheless, they require a double readout that implies a dedicated technical and construction effort. This is the “price” one has to pay in order to really “knock down” background. Stefano Pirro – NuMass 2010

  16. 147Sm- 2310 keV [ms] Rise time of the CaMoO4 crystal – no light detection Decay time of the CaMoO4 crystal – no light detection [au] Results on “large” crystals – 48Ca100MoO4 CaMoO4 is not a “perfect candidate” for future DBD Experiment since it contains 48Ca But this compound did show an extreme interesting feature The results are obtained on a ~160 g crystal CaMoO4 Bolometers permits alpha discrimination (99,8%) without Light detection Stefano Pirro – NuMass 2010

  17. / Zn82Se –an extremely promising compound (3) This compound shows another very interesting feature: ’s show different thermal pulse development rejection > 97 % without light detection Stefano Pirro – NuMass 2010

  18. No Light information - PSA This seems a characteristic of Molibdate crystals (also observed on other molibdates) Zn100MoO4 –A promising Molibdate (2) Light- Heat scatter plot Stefano Pirro – NuMass 2010

  19. Conclusions - I • We tested several types of scintillating crystals with interesting  emitters (100Mo,116Cd, 82Se, 48Ca) • Within them CdWO4 is “ready to use” • The “outsider” ZnSe is now, probably, the best candidate , even if some more tests are needed • Molibdates need more R&D both for radioactivity and scintillation light • This technique is the only one that can be used for several interesting DBD emitters with excellent energy • resolution (0.3  1 % FWHM) • Simulations show that a background level of 10-4 c/keV/kg/y can be “easily” reached without too much “restrictions” on internal radioactivity. • Within few months we plan to test 2 small arrays of CdWO4 and ZnSe crystals ( O(kg) ) in order to completely test the technique (unexpected “surprises” can always happen) • Particle Identification through Pulse Shape Analysis could result in a new, unexpected, ally Stefano Pirro – NuMass 2010

  20. CUORE 76Ge 116Cd 130Te 100Mo 82Se Gerda-Majorana 136 Xe SNO+ EXO Super-Nemo Conclusions-2 Different nuclei HAVE to be investigated by DBD experiments DBD Detectors with Q  >2615 keV can reach background levels  2 orders of magnitude smaller with respect to the others If we think about possible “ III generation experiments” the key point will be (if we consider solved the background issue….) Energy Resolution ( 1 %) Scintillating Bolometers are the only detectors that can fulfill all these 3 requirements Stefano Pirro – NuMass 2010

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