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Stefano Pirro LRT-2004 Sudbury December 13, 2004
Cleanliness backgrounds and surface contaminations in Cuore
Stefano Pirro INFN-Milano
Stefano Pirro LRT-2004 Sudbury December 13, 2004 Sum energy: 5407 keV
210Po α line
3600 keV
Bkg in DBD region
Continuum
2528 keV
Surface contaminations – bolometers
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Cuoricino
Cold finger
Tower
Roman Pb shield
Mixing chamber
Total mass40.9 kg
Cuoricino: 62 detectors array.11 module of 4 detectors 2 modules of 9 detectors
9 detectors 3x3x6 cm3, 340 g each
4 detectors 5x5x5 cm3, 790 g each
New limit 1024 y
The largest DBD experiment presently operating
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Direct measurements
The measured surface activity in the -region is
0.2 c/keV/kg/y 0.79 kg 150 cm2
0.003 c/cm2/day/MeV
This value is far away from the best alfa detector available ( 0.1 c/cm2/day/MeV)
The CUORE Goal implies a reduction on this value by a factor 10
The idea is therefore to do a indirect screening on materials
Perform a bolometric run deep underground
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Surface radioactivity levels in Cuoricino
The amount of radioactive contaminants are estimated from the background
Unfortunately this is not a simple task because it depends on several items
Roughness of the surfaces
Profile of the contamination
Statistics
Breaks in the secular equilibrium
Using the coincidences we estimate that 80 % of the background arise from copper
Assuming an exponential profile of the contaminations (λ=5 m), and matching low energy -peaks together with the continuum, we find an estimation of the surface radioactivity.
238U 1.6 10-10 g/g
232Th 7 10-10 g/g In the first 1 m
Stefano Pirro LRT-2004 Sudbury December 13, 2004
HR-ICPMS Measurements
Aim: 238U and 232Th contamination measurement in the surface layer (05 m thickness) of copper parts.
The idea is to remove by chemical attack a thin layer from the surface of the copper and then to measure U and Th concentration in the obtained solution via Mass Spectrometry.
Due to the Mass factor 50001000sol
etchCu
M
M
In order to reach sensitivity of 10-10 - 10-11 on the concentration in Cu
Reagents, containers tools must satisfy a purity of 10-14 g/g
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Measurements
Test measurements were performed at JCR-Lab - Ispra , Italy
VG-Axiom-Plus PTFE Container- pliers- thermometerSample during etchingSample draw
Etching rate 0.5 m/minute (2,5 % HNO3 at 45 °C)
5 samples + blank
Cu bar surface 100 cm2 amount of etsching solution 150 ml
ICPMS
VIS Spectrophotometric
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Measurements
Sample without STD
Cu X/Blank
Sample + STD 1
Sample + STD 2
Sample + STD 3
Sample without STD
Cu X/Time1
Sample without STD
Cu X/Time3
Sample step 3
CuX/Time3
Sample without STD
Cu X/Time4
Sample step 4
CuX/Time4
Sample step 5
Cu X/Time5
Copper sample in nitric acid solution
Blank sample
nitric acid solution
Sample + STD 1
Sample + STD 2
Sample + STD 3
Sample step 1
Cu X/Time1
Sample + STD 1
Sample + STD 2
Sample + STD 3
Sample + STD 1
Sample + STD 2
Sample + STD 3
Sample + STD 1
Sample + STD 2
Sample + STD 3
Sample without STD
Cu X/Time5
Sample without STD
Cu X/Time2
Sample step 2
Cu X/Time2
Sample + STD 1
Sample + STD 2
Sample + STD 3
Stefano Pirro LRT-2004 Sudbury December 13, 2004
ICPMS-Results
Systematic effects are not well understood
A possible solution is to increase the statistics (number of pieces)
TECM sample - integral measureTC sample - integral measure
Some points are not physically compatible
Problems arise in order to quote errors bars
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Direct Measurements
Hall C Cryostat Setup
Inside!More inside!
Eight 5x5x5 cm3 TeO2 crystals
10 days of LT measure to measure at 1 σ level the CUORICINO background
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Results
A radioactivity Test Run was performed during September-November 2004 (222 kgxd)
We changed both the copper treatment and the crystal lapping procedure
Unfortunately the background in the continuum showed no significant decrease
The surface radioactivity of the crystals is reduced by a factor 4 (match CUORE milestone)
230ThU232Th
No other lines are present with a limit of 0.2 Bq/kg (16 ppq for 238U)
4.4 10-17 g/g
Stefano Pirro LRT-2004 Sudbury December 13, 2004
Conclusions
Copper surface radioactivity remains the only task for CUORE
Different types of Copper treatment are under development
Chemical etching
Electro-etching
Electrochemical polishing
Plasma cleaning
Ion beam cleaning“Screening” HR ICPMS measurements started this year
Bolometric technique is the only one that gives the actual answer.
Thanks are due to the LNGS chemical lab and in particular to Dr. S. Nisi