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Radon Environment of Underground Experiment and Detection of Radon

Radon Environment of Underground Experiment and Detection of Radon. Lee, Myeong Jae DMRC, Seoul national university For the KIMS collaboration. Contents. Property of Radon Radioactivity of the rock for other experiments Radon detection for the KIMS experiments Radon-Free techniques

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Radon Environment of Underground Experiment and Detection of Radon

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  1. Radon Environment of Underground Experiment and Detection of Radon Lee, Myeong Jae DMRC, Seoul national university For the KIMS collaboration

  2. Contents • Property of Radon • Radioactivity of the rock for other experiments • Radon detection for the KIMS experiments • Radon-Free techniques • Conclusion

  3. Radon • Odorless, tasteless, invisible gas • Chemically inert and essentially non-reactive • Heaviest noble gas with highest melting and boiling point • Highly soluble in non-polar solvents • Moderately soluble in cold water • Able to diffuse through rock and soil • Decays by alpha particle emission (T1/2 = 3.8 days) • Exists in the typical atmosphere and specially in the underground environment • outside : 0.2 ~ 0.7 pCi/L • inside : ~ 1.25 pCi/L • residential recommendation : 4 pCi/L

  4. Decay chain of Radon

  5. Can cause lung cancer !! (From “Univ. of Minesota”) Why Radon is Important?

  6. Why Radon is Important?(2) • Radioactive contamination of experimental setup • Radon dissolves in water and contaminates all other material • Po ion easily attaches to other material • Can cause b.g. event • For the neutrino experiment radon daughter beta decay is significant bg source

  7. Radioactivity data for other experiment (From UKDMC Homepage)

  8. Sample Avg. Element(ppm) A B C D <0.5 U 3.46 <0.5 <0.5 <0.5 4.67 Th 1.89 2.20 9.02 5.58 Radioactive environment of Y2L Y2L 호상편마암 (~2Gyr) 중생대 화성암 (~200Myr)

  9. Radon Detection Method • No way to detect radon directly : Noble gas • Decay is detectable • alpha and its emitter detection • Lucas cell, SSNTD, electrostatic alpha spectroscopy, filter method, ionization detector • beta and its emitter detection • Liquid scintillator, beta spectroscopy, gamma counting

  10. Radon Detection Scheme (electrostatic alpha spectroscopy) 222Rn Decay 218Po(115keV) Stripping effect α (5.49MeV) 218Po+,+2 Attach to water, aerosol, oxygen (chemically stable) Decay 214Pb Decay 214Bi Electrostatic collection near photodiode Electrostatic collection near photodiode Decay α (6.00MeV) 214Po α (7.69MeV) Decay Detect

  11. Voltage Divider, Preamp Photodiode Radon Monitoring Detector • Electrostatic alpha spectroscopy • Use Si(Li) photodiode • 30mm X 30mm • Photodiode – chassis potential difference : -500V • Photodiode bias : -70V • Photodiode calibration : 210Po, 241Am • Neutralization of 218Po : Humidity control is necessary • Volume : ~ 70 liter

  12. Controller Moisture trap Radon detector Vacuum pump DAQ & Control computer Humidity, Temperature, Pressure, HV monitor Voltage Divider HV Supply Preamplifier HV Air Signal Shaping amplifier ADC Control Radon Detector Operation

  13. Data Histogram ADC ADC ADC Data Before Cut Data After Cut Mean time Mean time Calibration data analysis • Energy resolution is not good, • But we can distinguish two alpha particle. Typical Event Shape

  14. Typical signal and Background Air, ~0.74 Hz N2, ~0.0074 Hz 12h DAQ for typical air 6h DAQ for typical air and nitrogen 6.00MeV (218Po) 7.69MeV (214Po) Recent BG measurement = ~0.037Hz

  15. Standard Radon Source/ Calibration Setup • 226Ra in 5% HNO3 50g • Max. Activity : 130.3 Bq (at ~65days) = ~3500pCi = 50pCi/L * 70L • Made at 2004.4.17 at KRISS • Used at 2004.5.27 (34days after) : ~130.03Bq

  16. Radon detector Pump Temp. Humidity Sensor 11.5 liter/min X Flow meter Flow meter Filter 300cc/min 300cc/min Silicagel 280g, 452cc Grain size : Φ3mm X 222Rn 130.3Bq Total Event Po214 Decay Event Po218 Decay Event Calibration data analysis Calibration factor = (activity)/(event rate) [pCi/liter/Hz] ~1.8pCi/L/Hz = ~ 47Bq/Hz

  17. Radon detector (With know radon activity) X Temp. Humidity Sensor Pump Always ~74% at 25℃ 11.5 liter/min X Saturated solution X Flow meter Flow meter Salt (ex. NaCl) X ~74% at 25℃ NaCl saturated water Humidity Dependence Test Setup • Po positive ion easily attach to water molecule ⇒ “Neutralize” Po ion ⇒ Cannot detect alpha decay

  18. Humidity Dependence of Efficiency Humidity factor = (real event rate) / (expected event rate) Humidity factor Absolute humidity [kg/m3] Somewhat different with other experiment measurement

  19. Y2L Radon Level (pCi/Liter) Days elapsed since 2003.1.1

  20. Radioactivity data for other experiment Location Exp. U contents (ppb) Rn222 contents(pCi/L) Kamioka S-K, KamLand 0.8-1.3 Control room 5.4-54 Mine air. Seasonal dependence GranSasso DAMA, CRESST, Borexino 180~670 0.5-11 Mine air. Ventilation dependence 0.08-0.14 DAMA detector Sudbury SNO 1200 ~2.7 Mine air Boulby UKDMC ~10 Soudan CDMS 80~100 YYL KIMS ~ 500 ~1

  21. Radon-Free techniques • Blocking • Filtering • Ventilation

  22. Radon Blocking capability for various material

  23. Radon Blocking material :Example of KamLand

  24. Ventilation dependence of Radon

  25. Summary • Radon monitoring detector setup completed in Y2L • Radon contamination level monitoring in the air of Y2L is ongoing • Radioactivity in the rock is similar and radon activity is much lower than other experiment • Gamma background reduction from radon daughter elements in KIMS experiments is possible

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