2003-10-25 80th KPS meeting

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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