Underground Crystal Growth Marisa Pedretti

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

Participants ZARAGOZA Contractor Ge section Marisa Pedretti ? MPI HEIDELBERG Contractor

TeO 2 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: - TeO 2 powder formation - TeO 2 crystallization (platinum crucibles are used for both the steps) SICCAS grew for us 4 isotopically enriched crystals 5 cm 3 Marisa Pedretti

TeO 2 crystals: bulk contamination problem TeO 2 crystals: bulk contamination problem CUORICINO background spectrum alpha region – 190 Pt peak CUORICINO background spectrum alpha region – 190 Pt peak 190 Pt comes from the platinum crucibles used to grow them Marisa Pedretti the 190 Pt alpha peak could present a low energy tail extending down to the Q-value of 130 Te Double Beta Decay transition, and so contributing to the background

Possible effects of Pt contaminations Marisa Pedretti 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

Possible effects of Pt contaminations Marisa Pedretti Long pulse 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…)

Possible effects of Pt contaminations Marisa Pedretti Two (?) decay times 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…)

Possible effects of Pt contaminations Marisa Pedretti Two (?) decay times 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…)

Possible effects of Pt contaminations Marisa Pedretti Three decay times Difficulties in the data analysis Problem in global detector reproducibility Possible effects on the energy resolution 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…)

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

The idea 5x5x5 cm 3 crystal with an high Pt concentration crystal with a Pt contamination not detectable over bkg Marisa Pedretti Pt < 7.9e-08 g/g Pt = 7.9e-07 g/g

Possible explanation Heat bath TeO 2 crystal thermistor electrons thermistor lattice electron/phonon decoupling glue spots Teflon Gold Wires Pt crystal ICPMS measure  no uniform distribution 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 TeO 2 crystal one and so it could modify the pulse shape Which is the conductance between Pt and TeO 2 ? Which is its temperature law? Marisa Pedretti Anyway also if this is the obvious thermal model it is hard to obtain the observed pulse shapes with it.

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

“Spike Width (SW)” 1/4 Marisa Pedretti

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

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

1 st solution replace the Pt crucibles with Ir crucibles (Ir does not contain radioactive isotopes, but the effects on the pulse shape could persist) Marisa Pedretti “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. Answers from SICCAS (Chinese crystal company) To decrease the Pt contamination, we would like to make some modifications 1.use quartz crucible instead of Pt crucible for powder preparation 2.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.” not economically feasible

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

Results on Berkeley TeO 2 crystal We measured the Berkeley TeO 2 crystal on a Ge detector in the Baradello Lab Marisa Pedretti

Results on Berkeley TeO 2 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

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.