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

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

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

Workshop for Underground experiments and astroparticle physics 4 Decay chain of Radon232Th1.4e10yr238U3.5e9yr Ra5.75yr234Th24.10d 228Ac6.15h234Pa6.7h 228Th1.9yr234U2.5e5yr Ra3.65d230Th7.5e4yr Rn55.6s226Ra1600yr Po0.145s222Rn3.82d Pb10.6h218Po3.05m (~36%)212Bi60.6m(~64%) Po60.3us214Pb26.8m 208Tl3.05m Bi19.7m 208PbStable214Po164us Pb22.3yr 210Bi5.01d 210Po138.4d PbStable

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

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

Workshop for Underground experiments and astroparticle physics 7 Radioactivity data for other experiment (From UKDMC Homepage)

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

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

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

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

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

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.

Workshop for Underground experiments and astroparticle physics 14 Typical signal and Background Air, ~0.74 Hz N 2, ~ 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

Workshop for Underground experiments and astroparticle physics 15 Standard Radon Source / Calibration Setup  226Ra in 5% HNO 3 50g  Max. Activity : Bq (at ~65days) = ~3500pCi = 50pCi/L * 70L  Made at at KRISS  Used at (34days after) : ~130.03Bq

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

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 ℃

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

Workshop for Underground experiments and astroparticle physics 19 Y2L Radon Level Days elapsed since (pCi/Liter)

Workshop for Underground experiments and astroparticle physics 20 Radioactivity data for other experiment Mine air~ SNOSudbury ~10UKDMCBoulby 80~100CDMSSoudan ~1~ 500KIMSYYL DAMA detector Mine air. Ventilation dependence ~670DAMA, CRESST, Borexino GranSasso Mine air. Seasonal dependence Control room S-K, KamLand Kamioka Rn222 contents(pCi/L) U contents (ppb) Exp.Location

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

Workshop for Underground experiments and astroparticle physics 22 Radon Blocking capability for various material

Workshop for Underground experiments and astroparticle physics 23 Radon Blocking material :Example of KamLand

Workshop for Underground experiments and astroparticle physics 24 Ventilation dependence of Radon

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