1. 2003-10-25 80th KPS meeting 1 Development of Radon Monitoring Detector for the KIMS Experiment Lee, Myoung Jae DMRC, Seoul national university

2. 2003-10-25 80th KPS meeting 2 KIMS experiments  Korea Invisible Mass Search  Y2L : Yang-Yang underground Laboratory  Opened at 2003.4.  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

3. 2003-10-25 80th KPS meeting 3 Decay chain of Radon  Able to detect 6.00. 6.78, 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 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

4. 2003-10-25 80th 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

5. 2003-10-25 80th KPS meeting 5 Radon Monitoring Detector  Photodiode : 30mm X 30mm, ETRI  Volume : 70 liter Voltage Divider, Preamp Photodiode

6. 2003-10-25 80th 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

7. 2003-10-25 80th 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

8. 2003-10-25 80th 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)

9. 2003-10-25 80th 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

10. 2003-10-25 80th 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

11. 2003-10-25 80th 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