Underground Crystal Growth

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.