Underground Crystal Growth

1. Underground Crystal Growth Marisa Pedretti

2. Participants TeO2 section INFN (ITALY) (USA) Lawrence Berkeley National Laboratory University of South Carolina • LNGS • Como • Milano-Bicocca Contractor Non-EU Institutions Marisa Pedretti

3. Participants Ge section MPI HEIDELBERG ZARAGOZA ? Contractor Contractor Marisa Pedretti

4. 5 cm3 TeO2 crystals • our crystals are realized by the Chinese company • SICCAS (Shanghai) • we have checked in the past the radioactivity of the • metallic Te • the crystals are grown through two steps: • - TeO2 powder formation • - TeO2 crystallization • (platinum crucibles are used for both the steps) • SICCAS grew for us 4 isotopically • enriched crystals Marisa Pedretti

5. TeO2 crystals: bulk contamination problem CUORICINO background spectrum alpha region – 190Pt peak 190Pt comes from the platinum crucibles used to grow them the 190Pt alpha peak could present a low energy tail extending down to the Q-value of 130Te Double Beta Decay transition, and so contributing to the background Marisa Pedretti

6. Possible effects of Pt contaminations But it is possible that the Pt contamination could have a role also in an other Cuoricino problem: the pulse shape “zoology”. In Cuoricino, we have pulses with different shapes (long and double tails, fast rise time…) Normal: the shape is explainable with a simple thermal model Marisa Pedretti

7. Long pulse Possible effects of Pt contaminations But it is possible that the Pt contamination could have a role also in an other Cuoricino problem: the pulse shape “zoology”. In Cuoricino, we have pulses with different shapes (long and double tails, fast raise time…) Marisa Pedretti

8. Two (?) decay times Possible effects of Pt contaminations But it is possible that the Pt contamination could have a role also in an other Cuoricino problem: the pulse shape “zoology”. In Cuoricino, we have pulses with different shapes (long and double tails, fast raise time…) Marisa Pedretti

9. Possible effects of Pt contaminations But it is possible that the Pt contamination could have a role also in an other Cuoricino problem: the pulse shape “zoology”. In Cuoricino, we have pulses with different shapes (long and double tails, fast raise time…) Two (?) decay times Marisa Pedretti

10. Three decay times • Difficulties in the • data analysis • Problem in global • detector reproducibility • Possible effects on the • energy resolution Possible effects of Pt contaminations But it is possible that the Pt contamination could have a role also in an other Cuoricino problem: the pulse shape “zoology”. In Cuoricino, we have pulses with different shapes (long and double tails, fast raise time…) Marisa Pedretti

11. 3x3x6 cm3 crystal with a Pt contamination not detectable over bkg crystal with an high Pt concentration The idea We suspect a correlation between the Platinum concentration and a some shape parameter properly chosen Pt = 3.1e-06 g/g Pt < 1.2e-07 g/g Marisa Pedretti

12. The idea 5x5x5 cm3 Pt < 7.9e-08 g/g Pt = 7.9e-07 g/g crystal with a Pt contamination not detectable over bkg crystal with an high Pt concentration Marisa Pedretti

13. ICPMS measure  no uniform distribution Teflon thermistor electrons glue spots Heat bath Gold Wires thermistor lattice electron/phonon decoupling Which is the conductance between Pt and TeO2? Which is its temperature law? TeO2 crystal Pt crystal Possible explanation If all the platinum is concentrated in a unique cluster and if it is metallic, then it could have a heat capacity comparable with the TeO2 crystal one and so it could modify the pulse shape Anyway also if this is the obvious thermal model it is hard to obtain the observed pulse shapes with it. Marisa Pedretti

14. We think that the distortion introduced by the platinum inclusions regards the first part of the peak (fast and sharp) (not the long tails) Marisa Pedretti

15. PRELIMINARY WORK 1/4 “Spike Width (SW)” Marisa Pedretti

16. We used the contamination (taking in account of the BKG in the 3-4 MeV) • We use the “SW” parameter SW vs SW Pt contamination Marisa Pedretti

17. Attempt of quantification • We used the contamination (taking in account of the BKG in the 3-4 MeV) • We use the “SP” parameter SW vs Correlation index = 0.81 Marisa Pedretti

18. Answers from SICCAS (Chinese crystal company) “We have discussed on Iridium crucible issue. However, due to the brittleness of the Iridium, it's not easy to make the crucible for our Bridgman crystal growth. • To decrease the Pt contamination, we would like to make some modifications • use quartz crucible instead of Pt crucible for powder preparation • use low temperature in-gradient method to grow the crystal To make the experiment, we would need your funding of USD50,000 and in return we'll deliver you two pcs of 5x5x5 size crystals within three months.” 1st solution • replace the Pt crucibles with Ir crucibles • (Ir does not contain radioactive isotopes, • but the effects on the pulse shape could persist) not economically feasible Marisa Pedretti

19. 2nd solution • to change the crystallization method from • Bridgman to Czochralski (CZ), which in principle • avoids crucible contact with the triple phase • boundary We are in contact with two US companies in order to investigate the CZ method for TeO2. Trips in the US are planned to define crystal production with the CZ method, under the control of this WG. CRYSTAL TECHNOLOGY INC. INTEGRATED PHOTONIC INC. (IPI)

20. Results on Berkeley TeO2 crystal We measured the Berkeley TeO2 crystal on a Ge detector in the Baradello Lab Marisa Pedretti

21. Results on Berkeley TeO2 crystal We obtain a spectrum compatible with the limit of the Ge detector A measurement of the crystal is in program at LNGS Marisa Pedretti

22. Ge crystal growth 1) Contacts have been established with Canberra-Eurosys through the Spanish delegation, an enterprise called Tecnasa. They are contacting with the central offices and their preliminary results will be given to us in a future meeting. 2) Contacts have started directly with Canberra-Eurosys (in collaboration with german and Gran Sasso people), which has built Ge detectors for the Gran Sasso facility for radiopurity  measurements and is going to build also new Ge detectors for the corresponding Canfranc facility.