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Update on 222 Rn emanation measurements

This presentation provides an update on the 222Rn detection technique and new results from laboratory samples and the GERDA cryostat. The results show acceptable 222Rn emanation rates and demonstrate that 222Rn is homogeneously distributed in the cryostat volume. Further tests and investigations are planned.

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Update on 222 Rn emanation measurements

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  1. Update on 222Rn emanation measurements S. Lindemann, H. Richter, H. Simgen, G. Zuzel MPI für Kernphysik, Heidelberg GERDA general meeting, Padova Italy, 11-13.03.2009

  2. Outlook • 222Rn detection technique • New results – laboratory samples • New results – GERDA cryostat • Conclusions and future activities GERDA general meeting, Padova Italy, 11-13.03.2009

  3. 222Rn detection technique - Developed for the GALLEX/GNO experiment - Hand-made at MPI-K (~ 1 cm3 active volume) - In case of 222Rn only α-decays are detected 50 keV 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

  4. 222Rn detection technique MoREx Emanation chambers GERDA general meeting, Padova Italy, 11-13.03.2009

  5. New results – laboratory samples *) CRa226 = (5.4  0.2) Bq/kg **) CRa226 = (7.8  0.3) Bq/kg – only small 222Rn fraction is emanated GERDA general meeting, Padova Italy, 11-13.03.2009

  6. New results – laboratory samples Welds PT100 Welds MS GERDA general meeting, Padova Italy, 11-13.03.2009

  7. New results – laboratory samples Delrin MS GERDA general meeting, Padova Italy, 11-13.03.2009

  8. Shutter New results – laboratory samples Three-axial line GERDA general meeting, Padova Italy, 11-13.03.2009

  9. New results – GERDA cryostat Goal: ARn 14 mBq It has been decided to clean the cryostat (wiping) GERDA general meeting, Padova Italy, 11-13.03.2009

  10. New results – GERDA cryostat Cryostat after cleaning Sampling on the top and from the bottom (polyamide tube 8 m 81mm, ARn < 71 µBq) for 222Rn (in)homogeneity check Precise pressure drop (after sampling) measurement -> systematic error reduction MoREx P Cryostat GERDA general meeting, Padova Italy, 11-13.03.2009

  11. New results – GERDA cryostat Measurement procedure: • Taking a small sample (4 m3) from the bottom • Taking a small sample (4 m3) from the top • Adding cold, 222Rn-free nitrogen (mixing) • Taking a small sample (4 m3) from the bottom • Taking a big sample (26 m3) 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 222Rn (extractions/decay/production). Doing so one gets: Cb = (0.28 ± 0.03) mBq/m3 Ct = (0.42 ± 0.05) mBq/m3 Cb = (0.27 ± 0.05) mBq/m3 Ct = (0.23 ± 0.03) mBq/m3 A1 = (33.2 ± 4.0) mBq A3 = (31.3 ± 5.7) mBq A4 = (27.3 ± 2.5) mBq ---------------------------- Aav = (30.6 ± 2.4) mBq GERDA general meeting, Padova Italy, 11-13.03.2009

  12. New results – GERDA cryostat GERDA general meeting, Padova Italy, 11-13.03.2009

  13. Conclusions • Most of the samples show acceptable 222Rn 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 222Rn was homogeneously distributed in the cryostat volume • The systematic uncertainties were significantly reduced • Further tests with a completed cryogenic infrastructure foreseen • 222Rn emanation measurements of the commissioning lock (hall di montaggio) • Investigation of “cold” 222Rn emanation GERDA general meeting, Padova Italy, 11-13.03.2009

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