1. 2005-2-18 Workshop for Underground experiments and astroparticle physics 1 Radon Environment of Underground Experiment and Detection of Radon Lee, Myeong Jae DMRC, Seoul national university For the KIMS collaboration

2. 2005-2-18 Workshop for Underground experiments and astroparticle physics 2 Contents  Property of Radon  Radioactivity of the rock for other experiments  Radon detection for the KIMS experiments  Radon-Free techniques  Conclusion

3. 2005-2-18 Workshop for Underground experiments and astroparticle physics 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 (T 1/2 = 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. 2005-2-18 Workshop for Underground experiments and astroparticle physics 4 Decay chain of Radon232Th1.4e10yr238U3.5e9yr 4.014.20 228Ra5.75yr234Th24.10d 228Ac6.15h234Pa6.7h 228Th1.9yr234U2.5e5yr 5.424.77 224Ra3.65d230Th7.5e4yr 5.694.69 220Rn55.6s226Ra1600yr 6.294.78 216Po0.145s222Rn3.82d 6.785.49 212Pb10.6h218Po3.05m (~36%)212Bi60.6m(~64%)6.00 6.05212Po60.3us214Pb26.8m 208Tl3.05m8.79214Bi19.7m 208PbStable214Po164us 7.69 210Pb22.3yr 210Bi5.01d 210Po138.4d 5.30 206PbStable

5. 2005-2-18 Workshop for Underground experiments and astroparticle physics 5 Why Radon is Important? (From “Univ. of Minesota”) Can cause lung cancer !!

6. 2005-2-18 Workshop for Underground experiments and astroparticle physics 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. 2005-2-18 Workshop for Underground experiments and astroparticle physics 7 Radioactivity data for other experiment (From UKDMC Homepage)

8. 2005-2-18 Workshop for Underground experiments and astroparticle physics 8 Radioactive environment of Y2L U 3.46<0.5 Th 1.892.209.025.58 Element(ppm) ABCD Sample <0.5 4.67 Avg. Y2L 호상편마암 (~2Gyr) 중생대 화성암 (~200Myr)

9. 2005-2-18 Workshop for Underground experiments and astroparticle physics 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. 2005-2-18 Workshop for Underground experiments and astroparticle physics 10 Radon Detection Scheme (electrostatic alpha spectroscopy) 222 Rn 218 Po (115keV) α (5.49MeV) Stripping effect 218 Po +,+2 Electrostatic collection near photodiode Decay α (6.00MeV) Detect Attach to water, aerosol, oxygen (chemically stable) Decay 214 Pb Decay 214 Bi 214 Po α (7.69MeV) Electrostatic collection near photodiode Decay

11. 2005-2-18 Workshop for Underground experiments and astroparticle physics 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 : 210 Po, 241 Am  Neutralization of 218 Po : Humidity control is necessary  Volume : ~ 70 liter

12. 2005-2-18 Workshop for Underground experiments and astroparticle physics 12 Radon Detector Operation Radon detector Moisture trap Vacuum pump Voltage Divider Preamplifier Shaping amplifier ADC DAQ & Control computer HV Supply Humidity, Temperature, Pressure, HV monitor Controller HV Air Signal Control

13. 2005-2-18 Workshop for Underground experiments and astroparticle physics 13 Calibration data analysis Typical Event Shape Data Before Cut Mean time ADC Data After Cut Mean time ADC Data Histogram ADC  Energy resolution is not good,  But we can distinguish two alpha particle.

14. 2005-2-18 Workshop for Underground experiments and astroparticle physics 14 Typical signal and Background Air, ~0.74 Hz N 2, ~0.0074 Hz 12h DAQ for typical air 6h DAQ for typical air and nitrogen 6.00MeV ( 218 Po) 7.69MeV ( 214 Po) Recent BG measurement = ~0.037Hz

15. 2005-2-18 Workshop for Underground experiments and astroparticle physics 15 Standard Radon Source / Calibration Setup  226Ra in 5% HNO 3 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. 2005-2-18 Workshop for Underground experiments and astroparticle physics 16 Calibration data analysis Total EventPo214 Decay EventPo218 Decay Event Calibration factor = (activity)/(event rate) [pCi/liter/Hz] Radon detector Pump X Flow meter Filter Temp. Humidity Sensor X 300cc/min Silicagel 280g, 452cc Grain size : Φ3mm 11.5 liter/min 222Rn 130.3Bq ~1.8pCi/L/Hz = ~ 47Bq/Hz

17. 2005-2-18 Workshop for Underground experiments and astroparticle physics 17 Humidity Dependence Test Setup  Po positive ion easily attach to water molecule ⇒ “Neutralize” Po ion ⇒ Cannot detect alpha decay Always ~74% at 25 ℃ Saturated solution Salt (ex. NaCl) Radon detector (With know radon activity) Pump X Flow meter Temp. Humidity Sensor X 11.5 liter/min NaCl saturated water X X ~74% at 25 ℃

18. 2005-2-18 Workshop for Underground experiments and astroparticle physics 18 Humidity Dependence of Efficiency Humidity factor = (real event rate) / (expected event rate) Somewhat different with other experiment measurement Absolute humidity [kg/m 3 ] Humidity factor

19. 2005-2-18 Workshop for Underground experiments and astroparticle physics 19 Y2L Radon Level Days elapsed since 2003.1.1 (pCi/Liter)

20. 2005-2-18 Workshop for Underground experiments and astroparticle physics 20 Radioactivity data for other experiment Mine air~2.71200SNOSudbury ~10UKDMCBoulby 80~100CDMSSoudan ~1~ 500KIMSYYL DAMA detector0.08-0.14 Mine air. Ventilation dependence0.5-11180~670DAMA, CRESST, Borexino GranSasso Mine air. Seasonal dependence5.4-54 Control room0.8-1.3S-K, KamLand Kamioka Rn222 contents(pCi/L) U contents (ppb) Exp.Location

21. 2005-2-18 Workshop for Underground experiments and astroparticle physics 21 Radon-Free techniques  Blocking  Filtering  Ventilation

22. 2005-2-18 Workshop for Underground experiments and astroparticle physics 22 Radon Blocking capability for various material

23. 2005-2-18 Workshop for Underground experiments and astroparticle physics 23 Radon Blocking material :Example of KamLand

24. 2005-2-18 Workshop for Underground experiments and astroparticle physics 24 Ventilation dependence of Radon

25. 2005-2-18 Workshop for Underground experiments and astroparticle physics 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