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 210 Po 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 mass 40.9 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 cm 3, 790 g each New limit 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 cm c/cm 2 /day/MeV This value is far away from the best alfa detector available (  0.1 c/cm 2 /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. 238 U  g/g 232 Th  g/g In the first 1  m

Stefano Pirro LRT-2004 Sudbury December 13, 2004 HR-ICPMS Measurements Aim: 238 U and 232 Th contamination measurement in the surface layer (0  5  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 In order to reach sensitivity of on the concentration in Cu Reagents, containers tools must satisfy a purity of 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- thermometer Sample during etching Sample draw Etching rate  0.5  m/minute (2,5 % HNO3 at 45 °C) 5 samples + blank Cu bar surface  100 cm 2 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 measure TC 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 cm 3 TeO 2 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) 230 Th U 232 Th No other lines are present with a limit of 0.2  Bq/kg (16 ppq for 238 U) 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