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INFN Sezione di Roma, ITALY

TeO 2 crystals for DBD experiments. I.Dafinei. INFN Sezione di Roma, ITALY. introduction TeO 2 crystal general properties crystal growth specific requirements for DBD use large scale production problems TeO 2 chemistry crystal growth and processing transport and storage

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INFN Sezione di Roma, ITALY

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  1. TeO2 crystals for DBD experiments I.Dafinei INFN Sezione di Roma, ITALY

  2. introduction TeO2 crystal general properties crystal growth specific requirements for DBD use large scale production problems TeO2 chemistry crystal growth and processing transport and storage potential developments conclusion content

  3. why TeO2 ? • 130Te largest isotopic abundance • existing industrial production of an “easy to find” compound • accessible price ββ emitters of experimental interest 2b - CUORE module: 4 x 760g 2.530MeV TeO2 crystal 5x5x5 cm3 Crystals of TeO2 are detector and source why DBD ? why TeO2 ? • why DBD ? • neutrino oscillation experiments can give only: • values of mixing angles • mass differences (predict range of effective mass) • DBD measurements may: • give the scale of neutrino mass • demonstrate the Maiorana nature of neutrino

  4. TeO2 (paratellurite) short:: 1.88 Å long:: 2.12 Å a = 4.8088 Å c = 7.6038 Å • relatively low melting point • distorted rutile (TiO2) structure • anisotropy of expansion coefficient TeO2 general properties

  5. seed Czochralski grown Xtal molten TeO2 molten TeO2 grown Xtal heating seed Pt “crucibles” filled with TeO2 powder Bridgman as grown TeO2 crystal ingot • Bridgman grown crystals are more stressed than Czochralski ones • annealing at about 550°C helps in removing the residual stresses TeO2 crystal growth • TeO2 crystal is particularly repellent to impurities • most of radioactive isotopes have ionic characteristics incompatible with substitutional incorporation in TeO2

  6. natural radioactivity activation products crucible material main radioactive series DBD requirements radio-purity

  7. see S. Capelli “Simulation of the CUORE background … major production problems come from (radio)purity constraints bulk surface internal external • cannot be avoided by shielding • vetoes do not always work contamination: rough estimation of impurity levels • radio-purity quality control during production is impossible • freeze production conditions found in the R&D phase • sampling radio-purity check of raw materials and consumables • special precaution during operation and handling solution impurity allowed (g/g): T ≥ 1024 yr Ti < 1010 yr close to or below detection limit of most sensitive techniques used for quantitative elemental analysis (NAA, ICP-MS) large scale production problems TeO2 crystals currently produced at industrial scale for acousto-optics applications have mechanical and optical characteristics much above DBD application requirements

  8. compliance with radio-purity requirements large scale production problems (continued) • intermediary products • TeO2 powder (after densification by calcination) • 238U < 2*10-10 g/g • 232Th < 2*10-10 g/g • 210Pb < 10-4 Bq/kg • 40K < 10-3 Bq/kg • 60Co < 4*10-5 Bq/kg • Pt contamination in as grown crystals • Pt (element) < 10-10 g/g • 190Pt (isotope) < 3*10-6 Bq/kg • final product • (TeO2 crystal ready-to-use) • 238U < 3*10-13 g/g • 232Th < 3*10-13 g/g • 210Pb < 10-5 Bq/kg • 60Co < 10-6 Bq/kg • raw materials and reactants • Te metal contamination • 238U < 2*10-10 g/g • 232Th < 2*10-10 g/g • 210Pb < 10-4 Bq/kg • 40K < 10-3 Bq/kg • 60Co < 10-5 Bq/kg • acids contamination • 238U < 5*10-12 g/g • 232Th < 5*10-12 g/g • water contamination • 238U < 4*10-12 g/g • 232Th < 4*10-12 g/g • contamination of other liquids • 238U < 5*10-12 g/g • 232Th < 5*10-12 g/g

  9. refining TeO2 @ SICCAS Te HNO3 2Te+9HNO3 → Te2O3(OH)NO3+8NO2+4H2O Te2O3(OH)NO3→2 TeO2+HNO3 TeO2 washing HCl TeCl4 TeO2 TeO2+HCl→TeCl4+H2O grinded filtering NH4OH TeCl4+4NH4OH→Te(OH)4+4NH4Cl Te(OH)4→TeO2+H2O TeCl4 TeO2 1/3 ingot selected washing, drying calcination 1st Xtal growth TeO2 99.999% calcination 2nd Xtal growth TeO2 chemistry

  10. future CUORE crystals growth unit @ SICCAS Technological space growth control room crystal growth room Pt crucibles preparation place on duty Annealing storage room TeO2 growth CUORE crystals production at SICCAS • specially dedicated technological area • separated raw material circuit • separated consumables and ancillaries circuit • production flow survey by parallel sampling radio-contamination control of raw materials, consumables and ancillaries (SINAP)

  11. SICCAS / INFN clean room ultra-pure water generator (2) • class 1000 qualified • general standard respected • easy maintenance guarantee • ultrapure water 300 l/h P/B chemical etching and polishing • clean surrounding dressing room 1 dressing room 2 packaging • Xray difractometer • lapping bench • ultrasound washer • microwave oven • chemical etching bench • polishing bench • packaging bench passage air shower ultra-pure water generator (1) outer storage area final shaping and lapping 1 m TeO2 crystal processing

  12. SICCAS / INFN clean room TeO2 crystal processing(continued)

  13. see S. Cebrian's talk "Status of the Cosmogenic-induced-activity task” transport and storage Measurements of activation cross sections in proton beams CERN PS and ISOLDE • cosmogenic contamination • total exposure time to cosmic rays from metallic Te synthesis to LNGS delivery must be less than 6 months • setting-up of a dedicated underground storage at SICCAS is on the way Ettore Fiorini, CUORE meeting Como, Feb.21-23, 2007

  14. enriched TeO2 ? first tests, bad experience scintillating TeO2 ? other research directions? search for the Double Beta Decay of 120Te (0.09% abundance) ______ 120Sb ______ 120Te e e ______ 120Sn potential developments • Nucl.Instr.Meth.in Phys.Res. A 554, Issues 1-3 , 1 December 2005, 195-200 • SCINT2005 Proc. 8th Int. Conf., Alushta, Crimea, Ukraine, Sept. 19-23, 2005, pp. 106-108 • phys. stat. sol. (a) 204, No. 5, 1567–1570 (2007) / DOI 10.1002/pssa.200622458 DBD2: (A,Z) + 2 e- (A,Z-2) + 2neallowed by SM (A,Z) + e- (A,Z-2) + e+ + 2ne (A,Z)  (A,Z-2) + 2 e+ + 2ne DBD0: decays with no neimplies physics beyond SM see E.B. Norman et al in CUORE GM, LNGS June 2007

  15. low temperature scintillation in TeO2 photo-luminescence X-ray excited luminescence potential developments • conclusions on luminescence origin • excitonic nature of instrinsic photoluminescence in TeO2 (STE recombination) • in the case of radio-luminescence the contribution of different luminescent centre becomes preponderant (possibly defect states related to oxygen vacancies and consequent Te2+ defect presence, i.e. local states in forbidden band) • complete quenching of scintillation at 10mK must be due to a very active trapping process

  16. TeO2 crystal is among the best choices for DBD experiments growth and processing of TeO2 crystals having a radio-purity compatible with foreseen CUORE total background of 0.001 counts/keV/kg/y is a very challenging task joint efforts from INFN (Italy) and SICCAS (China) may fulfill this task conclusion

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