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2003-10-25 80th KPS meeting
1
Development of Radon Monitoring Detector for the KIMS Experiment
Lee, Myoung Jae
DMRC, Seoul national university
2003-10-25 80th KPS meeting
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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 need
s Radon monitoring is necess
ary to check the systematic effect of the gamma background generated from the radon daughter elements
2003-10-25 80th KPS meeting
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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 : 220Rn < ~10 % of 222Rn Consider 222Rn only
232Th232Th1.4e10yr1.4e10yr
238U238U3.5e9yr3.5e9yr
4.014.01 4.204.20228Ra228Ra5.75yr5.75yr
234Th234Th24.10d24.10d
228Ac228Ac6.15h6.15h
234Pa234Pa6.7h6.7h
228Th228Th1.9yr1.9yr
234U234U2.5e5yr2.5e5yr
5.425.42 4.774.77224Ra224Ra3.65d3.65d
230Th230Th7.5e4yr7.5e4yr
5.695.69 4.694.69220Rn220Rn55.6s55.6s
226Ra226Ra1600yr1600yr
6.296.29 4.784.78216Po216Po0.145s0.145s
222Rn222Rn3.82d3.82d
6.786.78 5.495.49212Pb212Pb10.6h10.6h
218Po218Po3.05m3.05m
(~36%)(~36%)212Bi212Bi60.6m60.6m (~64%)(~64%)
6.006.00
6.056.05 212Po212Po60.3us60.3us
214Pb214Pb26.8m26.8m
208Tl208Tl3.05m3.05m
8.798.79 214Bi214Bi19.7m19.7m
208Pb208PbStableStable
214Po214Po164us164us
7.697.69210Pb210Pb22.3yr22.3yr
210Bi210Bi5.01d5.01d
210Po210Po138.4d138.4d
5.305.30206Pb206PbStableStable
2003-10-25 80th KPS meeting
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Radon Monitoring Detector (Cont.)
Electrostatic alpha spectroscopy Use Si(Li) photodiode Photodiode – chassis potential differ
ence : -500V
Photodiode bias : -70V Photodiode calibration
: 210Po, 241Am Neutralization of 218Po
: Humidity control is necessary
2003-10-25 80th KPS meeting
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Radon Monitoring Detector
Photodiode : 30mm X 30mm, ETRI Volume : 70 liter
Voltage Divider,Preamp
Photodiode
2003-10-25 80th KPS meeting
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Radon Monitoring Detector (Cont.)
Radondetector
Moisture trap
Vacuum pump
VoltageDivider
Preamplifier
Shapingamplifier
Gate generator
Delay Gate generator
ADC
DAQ & Controlcomputer
HV Supply
Humidity, Temperature sensorPressure gauge
Controller
HV
Air
Signal
Control
2003-10-25 80th KPS meeting
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Radon Detection Scheme
222Rn
218Po (115keV)
α (5.49MeV)Stripping effect
218Po+,+2
Electrostatic collection near photodiode
Decay
α (6.00MeV)
DetectDetect
Attach to water, aerosol, oxyzen
(chemically stable)Decay
214PbDecay214Bi
214Po
α (7.69MeV)
Electrostatic collection near photodiode
Decay
Decay
2003-10-25 80th KPS meeting
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Typical signal and Background
Air, 2658 event/hour
N2, 26.8 event/hour
12h DAQ for typical air
6h DAQ for typical air and nitrogen6.00MeV
(218Po)7.69MeV
(214Po)
2003-10-25 80th KPS meeting
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Radon Contamination mesurement
Nitrogen test for ~9days: Time evolution of alpha counts
Nitrogen test for ~9days: (218Po count) / (214Po count)
Radon contamination of radon detector does not matter in this experiment setup (1h DAQ each time)
Equilibrium
214Po count218Po count
2003-10-25 80th KPS meeting
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Radon level of the air in the Y2L
(~9 day run data)214Po count218Po count214Po count average
Alpha counts to 222Rn level calibration
Used 214Po event only 222Rn 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
2003-10-25 80th KPS meeting
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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