underground crystal growth
DESCRIPTION
Underground Crystal Growth. Marisa Pedretti. Participants. TeO 2 section. INFN (ITALY). (USA). Lawrence Berkeley National Laboratory University of South Carolina. LNGS Como Milano-Bicocca. Contractor. Non-EU Institutions. Marisa Pedretti. Participants. Ge section. MPI - PowerPoint PPT PresentationTRANSCRIPT
Underground Crystal Growth
Marisa Pedretti
Participants Participants
INFN(ITALY)
• LNGS• Como• Milano-Bicocca
Contractor
Lawrence Berkeley National Laboratory
University of South Carolina
•
•
(USA)
Non-EU Institutions
TeO2 section
Marisa Pedretti
Participants Participants
ZARAGOZA
Contractor
Ge section
Marisa Pedretti
?
MPI HEIDELBERG
Contractor
TeO2 crystalsTeO2 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
5 cm3
Marisa Pedretti
TeO2 crystals:bulk contamination problem
TeO2 crystals:bulk contamination problem
CUORICINO background spectrumalpha region – 190Pt peak
CUORICINO background spectrumalpha region – 190Pt peak
190Pt comes from the platinum crucibles used to grow them
Marisa Pedretti
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
Possible effects of Pt contaminations
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
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
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
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
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 ideaThe idea
3x3x6 cm3
crystal with an high Pt concentration
crystal with a Pt contamination not
detectable over bkg Marisa Pedretti
Pt = 3.1e-06 g/g Pt < 1.2e-07 g/g
We suspect a correlation between the Platinum concentration and a some shape parameter properly chosen
The ideaThe idea
5x5x5 cm3
crystal with an high Pt concentration
crystal with a Pt contamination not
detectable over bkg
Marisa Pedretti
Pt < 7.9e-08 g/gPt = 7.9e-07 g/g
Possible explanationPossible explanation
Heatbath
TeO2
crystal
thermistorelectrons
thermistorlattice
electron/phonondecoupling
glue spots
Teflon
Gold Wires
Ptcrystal
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 TeO2 crystal one and so it could modify the pulse shape
Which is the conductance
between Pt and TeO2?
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
FWHM pulse % contamination
0
5
10
15
20
25
30
35
40
-20,0 0,0 20,0 40,0 60,0 80,0 100,0 120,0
Serie1
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
ln (FWHM pulse) % ln (Pt cont)
y = -0,3069x + 3,3943
R2 = 0,6514
0
0,5
1
1,5
2
2,5
3
3,5
4
-1 0 1 2 3 4 5
Correlation index = 0.81
Marisa Pedretti
SW vs
1st solution1st 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 andin 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
2nd solution2nd solution
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.
INTEGRATED PHOTONIC INC. (IPI)
CRYSTAL TECHNOLOGY INC.
Results on Berkeley TeO2 crystalResults on Berkeley TeO2 crystal
We measured the Berkeley TeO2 crystal on a Ge detector in the Baradello Lab
Marisa Pedretti
Results on Berkeley TeO2 crystalResults 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
Ge crystal growthGe 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.