th KPS meeting 1 Development of Radon Monitoring Detector for the KIMS Experiment Lee, Myoung Jae DMRC, Seoul national university

th KPS meeting 2 KIMS experiments  Korea Invisible Mass Search  Y2L : Yang-Yang underground Laboratory  Opened at  Located YangYang pumped water power plant  Dark matter (WIMP) search experiment using CsI crystal detector  Recoil energy : ~ few keV  Low gamma background needs  Radon monitoring is necessary to check the systematic effect of the gamma background generated from the radon daughter elements

th KPS meeting 3 Decay chain of Radon  Able to detect , 7.59, 8.79MeV alpha separately  Rock  U : < 0.5 ppm  Th : ~5.6 ppm  Air : 220 Rn < ~10 % of 222 Rn  Consider 222 Rn only232Th1.4e10yr238U3.5e9yr 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

th KPS meeting 4 Radon Monitoring Detector (Cont.)  Electrostatic alpha spectroscopy  Use Si(Li) photodiode  Photodiode – chassis potential difference : -500V  Photodiode bias : -70V  Photodiode calibration : 210 Po, 241 Am  Neutralization of 218 Po : Humidity control is necessary

th KPS meeting 5 Radon Monitoring Detector  Photodiode : 30mm X 30mm, ETRI  Volume : 70 liter Voltage Divider, Preamp Photodiode

th KPS meeting 6 Radon Monitoring Detector (Cont.) Radon detector Moisture trap Vacuum pump Voltage Divider Preamplifier Shaping amplifier Gate generator DelayGate generator ADC DAQ & Control computer HV Supply Humidity, Temperature sensor Pressure gauge Controller HV Air Signal Control

th KPS meeting 7 Radon Detection Scheme 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, oxyzen (chemically stable) Decay 214 Pb Decay 214 Bi 214 Po α (7.69MeV) Electrostatic collection near photodiode Decay

th KPS meeting 8 Typical signal and Background Air, 2658 event/hour N 2, 26.8 event/hour 12h DAQ for typical air 6h DAQ for typical air and nitrogen 6.00MeV ( 218 Po) 7.69MeV ( 214 Po)

th KPS meeting 9 Radon Contamination mesurement Nitrogen test for ~9days : Time evolution of alpha counts Nitrogen test for ~9days : ( 218 Po count) / ( 214 Po count)  Radon contamination of radon detector does not matter in this experiment setup (1h DAQ each time) Equilibrium 214 Po count 218 Po count

th KPS meeting 10 Radon level of the air in the Y2L (~9 day run data) 214 Po count 218 Po count 214 Po count average  Alpha counts to 222 Rn level calibration  Used 214 Po event only  222 Rn level in Y2L  Mean : 2.68pCi/liter  Min : 1.51pCi/liter  Max : 3.79pCi/liter  Measurement is undergoing now  Cf)  2002 년 환경부 조사 : 0.5~2 pCi/liter  미국 환경부 권고기준 : 4 pCi/liter

th KPS meeting 11 Conclusion  Radon monitoring detecter setup completed in Y2L  Electrostatic, use Si photodiode  Radon contamination level monitoring in the air of Y2L is ongoing  Gamma background reduction from radon daughter elements in KIMS experiments is possible