Update on 222Rn emanation measurements

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Update on 222Rn emanation measurements

• S. Lindemann, H. Richter, H. Simgen, G. Zuzel
• MPI für Kernphysik, Heidelberg

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Outlook

• 222Rn detection technique
• New results laboratory samples
• New results GERDA cryostat
• Conclusions and future activities

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222Rn detection technique
- Developed for the GALLEX/GNO experiment -
Hand-made at MPI-K ( 1 cm3 active volume) - In
case of 222Rn only a-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)
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222Rn detection technique
MoREx
Emanation chambers
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New results laboratory samples
) CRa226 (5.4 ? 0.2) Bq/kg ) CRa226
(7.8 ? 0.3) Bq/kg only small 222Rn fraction is
emanated
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New results laboratory samples
Welds
PT100
Welds
MS
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New results laboratory samples
Delrin
MS
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New results laboratory samples
Three-axial line
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New results GERDA cryostat
Goal ARn ? 14 mBq It has been decided to clean
the cryostat (wiping)
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New results GERDA cryostat
Cryostat after cleaning Sampling on the top and
from the bottom (polyamide tube 8 m 8?1mm, ARn lt
71 µBq) for 222Rn (in)homogeneity check Precise
pressure drop (after sampling) measurement -gt
systematic error reduction
MoREx
P
Cryostat
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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
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New results GERDA cryostat
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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 -gt 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