Update on 222 Rn emanation measurements S Lindemann

Update on 222 Rn emanation measurements S. Lindemann, H. Richter, H. Simgen, G. Zuzel MPI für Kernphysik, Heidelberg GERDA general meeting, Padova Italy, 11 -13. 03. 2009

Outlook o o 222 Rn detection technique New results – laboratory samples New results – GERDA cryostat Conclusions and future activities GERDA general meeting, Padova Italy, 11 -13. 03. 2009

222 Rn detection technique - Developed for the GALLEX/GNO experiment - Hand-made at MPI-K (~ 1 cm 3 active volume) - In case of 222 Rn only α-decays are detected 50 ke. V threshold - bcg: 0. 1 – 2 cpd - detection efficiency of ~ 50% - Special filling line needed (blank value of ~10 µBq) - Absolute detection limit ~ 30 µBq (15 Rn atoms) GERDA general meeting, Padova Italy, 11 -13. 03. 2009

222 Rn detection technique Mo. REx Emanation chambers GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – laboratory samples Sample Emanation rate Remarks Steel plates without welds < 0. 1 m. Bq <0. 4 m. Bq/m 2 4 plates, ~0. 26 m 2 (brushed, acetone wiping) Steel plates with welds < 0. 1 m. Bq <0. 03 m. Bq/m 4 plates, 3. 2 m, 62 A (brushed, acetone wiping) < 50 µBq Cylinder, 380 cm 2, 43 g (6. 6 0. 5) Bq/piece Steel encaps. , 10 pieces (0. 36 0. 03) m. Bq Cryostat < 20 µBq Cryostat Shutter valve (0. 92 0. 03) m. Bq Cryostat Three-axial cryo-line (LN 2/LAr) (0. 25 0. 04) m. Bq Cryo-infrastructure Molecular sieve zeolite Z 10* (2. 2 0. 1) Bq/kg WARP, air prepurification Molecular sieve zeolite Z 4** (0. 12 0. 01) Bq/kg WARP, air dehydrattion Delrin PT 100 sensors Lenght measuring device CF-40 flange with a glass window *) CRa 226 = (5. 4 0. 2) Bq/kg **) CRa 226 = (7. 8 0. 3) Bq/kg – only small 222 Rn fraction is emanated GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – laboratory samples Welds PT 100 Welds MS GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – laboratory samples Delrin MS GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – laboratory samples Three-axial line Shutter GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – GERDA cryostat Sample description Single results [m. Bq] Av. value [m. Bq] 1 st test, SIMIC in Nov. 2007 16. 9 1. 6 stat 3. 0 sys 29. 8 2. 4 stat 5. 8 sys 23. 3 3. 6 Empty cryostat after cleaning, no N 2 mixing prior to extractions 2 nd test, SIMIC/GS in March 2008 13. 6 0. 7 stat 2. 4 sys 13. 7 0. 7 stat 2. 7 sys 13. 7 1. 9 Empty cryostat, after additional cleaning performed at SIMIC 4 th test, GS in June 2008 33. 0 2. 8 stat 7. 0 sys 35. 7 2. 9 stat 8. 8 sys 34. 4 6. 0 6 weeks after the 3 rd test. Results indicate residual air-born Rn present in the cryostat during 3 rd test. Comments Goal: ARn 14 m. Bq It has been decided to clean the cryostat (wiping) GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – GERDA cryostat Cryostat after cleaning Sampling on the top and from the bottom (polyamide tube 8 m 8 1 mm, ARn < 71 µBq) for 222 Rn (in)homogeneity check Precise pressure drop (after sampling) measurement -> systematic error reduction Mo. REx P Cryostat GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – GERDA cryostat Measurement procedure: o o o Taking a small sample (4 m 3) from the bottom Taking a small sample (4 m 3) from the top Adding cold, 222 Rn-free nitrogen (mixing) Taking a small sample (4 m 3) from the bottom Taking a big sample (26 m 3) from the top To compare obtained concentrations and finally to find the total emanation rate of the cryostat one has to calculate back and normalize the measured activities taking into account the amount of extracted gas and changes in the activities in the remaining 222 Rn (extractions/decay/production). Doing so one gets: Cb = (0. 28 ± 0. 03) m. Bq/m 3 Ct = (0. 42 ± 0. 05) m. Bq/m 3 Cb = (0. 27 ± 0. 05) m. Bq/m 3 Ct = (0. 23 ± 0. 03) m. Bq/m 3 A 1 = (33. 2 ± 4. 0) m. Bq A 3 = (31. 3 ± 5. 7) m. Bq A 4 = (27. 3 ± 2. 5) m. Bq --------------Aav = (30. 6 ± 2. 4) m. Bq GERDA general meeting, Padova Italy, 11 -13. 03. 2009

New results – GERDA cryostat Sample description Single results [m. Bq] Av. value [m. Bq] 1 st test, SIMIC in Nov. 2007 16. 9 1. 6 stat 3. 0 sys 29. 8 2. 4 stat 5. 8 sys 23. 3 3. 6 Empty cryostat after cleaning, no N 2 mixing prior to extractions 2 nd test, SIMIC/GS in March 2008 13. 6 0. 7 stat 2. 4 sys 13. 7 0. 7 stat 2. 7 sys 13. 7 1. 9 Empty cryostat, after additional cleaning performed at SIMIC 4 th test, GS in June 2008 33. 0 2. 8 stat 7. 0 sys 35. 7 2. 9 stat 8. 8 sys 34. 4 6. 0 6 weeks after the 3 rd test. Results indicate residual air-born Rn present in the cryostat during 3 rd test. 5 th test GS in Nov. 2008 33. 2 3. 5 stat 1. 9 sys 31. 3 4. 6 stat 3. 4 sys 27. 3 2. 4 stat 0. 7 sys 30. 6 2. 4 After wiping of Cu / steel surface. Precise pressure reading. In the last extraction the biggest gas volume was processed Comments GERDA general meeting, Padova Italy, 11 -13. 03. 2009

Conclusions o o o o Most of the samples show acceptable 222 Rn emanation rates (shutter valve, three-axial line, . . . ) The impact of the last cryostat cleaning on its emanation rate was very minor (solutions -> talk of B. Schwingenheuer) It has been shown that 222 Rn was homogeneously distributed in the cryostat volume The systematic uncertainties were significantly reduced Further tests with a completed cryogenic infrastructure foreseen 222 Rn emanation measurements of the commissioning lock (hall di montaggio) Investigation of “cold” 222 Rn emanation GERDA general meeting, Padova Italy, 11 -13. 03. 2009