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2005-2-18 Workshop for Underground experiments and astroparticle physics
1
Radon Environment of Underground Experiment and Detection of Radon
Lee, Myeong Jae
DMRC, Seoul national universityFor the KIMS collaboration
2005-2-18 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
2005-2-18 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 (T1/2 = 3.8 days) Exists in the typical atmosphere and specially in the unde
rground environment outside : 0.2 ~ 0.7 pCi/L inside : ~ 1.25 pCi/L residential recommendation : 4 pCi/L
2005-2-18 Workshop for Underground experiments and astroparticle physics 4
Decay chain of Radon 232Th232Th
1.4e10yr1.4e10yr238U238U
3.5e9yr3.5e9yr 4.014.01 4.204.20
228Ra228Ra5.75yr5.75yr
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
226Ra226Ra1600y1600y
rr6.296.29 4.784.78
216Po216Po0.1450.145
ss
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 212Po212Po60.3u60.3u
ss
214Pb214Pb26.8m26.8m
208Tl208Tl3.05m3.05m
8.798.79 214Bi214Bi19.7m19.7m
208Pb208PbStableStable
214Po214Po164us164us
7.697.69210Pb210Pb22.3yr22.3yr
210Bi210Bi5.01d5.01d
210Po210Po138.4138.4
dd5.305.30
206Pb206PbStableStable
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Why Radon is Important?
(From “Univ. of Minesota”)
Can cause lung cancer !!
2005-2-18 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 deca
y is significant bg source
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Radioactivity data for other experiment
(From UKDMC Homepage)
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Radioactive environment of Y2L
U 3.46 <0.5 <0.5 <0.5
Th 1.89 2.20 9.02 5.58
Element(ppm) A B C D
Sample
<0.5
4.67
Avg.
Y2L
호상편마암(~2Gyr)
중생대 화성암(~200Myr)
2005-2-18 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 me
thod, ionization detector beta and its emitter detection
Liquid scintillator, beta spectroscopy, gamma counting
2005-2-18 Workshop for Underground experiments and astroparticle physics 10
Radon Detection Scheme (electrostatic alpha spectroscopy)
222Rn
218Po (115keV)
α (5.49MeV)Stripping effect
218Po+,+2
Electrostatic collection near photodiode
Decay
α (6.00MeV)
DetectDetect
Attach to water, aerosol, oxygen
(chemically stable)Decay
214PbDecay214Bi
214Po α (7.69MeV)
Electrostatic collection near photodiode
Decay
Decay
2005-2-18 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 : 210Po, 241Am Neutralization of 218Po
: Humidity control is necessary Volume : ~ 70 liter
2005-2-18 Workshop for Underground experiments and astroparticle physics 12
Radon Detector Operation
Radondetector
Moisture trap
Vacuum pump
VoltageDivider
Preamplifier
Shapingamplifier
ADC
DAQ & Controlcomputer
HV Supply
Humidity, Temperature, Pressure, HV monitor
Controller
HV
Air
Signal
Control
2005-2-18 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.
2005-2-18 Workshop for Underground experiments and astroparticle physics 14
Typical signal and Background
Air, ~0.74 Hz
N2, ~0.0074 Hz
12h DAQ for typical air
6h DAQ for typical air and nitrogen6.00MeV
(218Po)7.69MeV
(214Po)
Recent BG measurement = ~0.037Hz
2005-2-18 Workshop for Underground experiments and astroparticle physics 15
Standard Radon Source/ Calibration Setup
226Ra in 5% HNO3 50g Max. Activity : 130.3 Bq (at ~65days)
= ~3500pCi = 50pCi/L * 70L Made at 2004.4.17 at KRISS Used at 2004.5.27 (34days after) : ~130.03Bq
2005-2-18 Workshop for Underground experiments and astroparticle physics 16
Calibration data analysis
Total Event Po214 Decay Event Po218 Decay Event
Calibration factor = (activity)/(event rate) [pCi/liter/Hz]
Radon detector
Pump
X Flow meter Flow meter Filter
Temp. Humidity Sensor
X300cc/min 300cc/min Silicagel 280g, 452cc
Grain size : Φ3mm
11.5 liter/min
222Rn 130.3Bq
~1.8pCi/L/Hz= ~ 47Bq/Hz
2005-2-18 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 Flow meter
Temp. Humidity Sensor
X
11.5 liter/min
NaCl saturated water
X
X
~74% at 25℃
2005-2-18 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/m3]
Humidity factor
2005-2-18 Workshop for Underground experiments and astroparticle physics 19
Y2L Radon Level
Days elapsed since 2003.1.1
(pC
i/Lite
r)
2005-2-18 Workshop for Underground experiments and astroparticle physics 20
Radioactivity data for other experiment
Mine air~2.71200SNOSudbury
~10UKDMCBoulby
80~100CDMSSoudan
~1~ 500KIMSYYL
DAMA detector0.08-0.14
Mine air. Ventilation dependence0.5-11180~670DAMA, CRESST, Borexino
GranSasso
Mine air. Seasonal dependence5.4-54
Control room0.8-1.3S-K, KamLand
Kamioka
Rn222 contents(pCi/L)
U contents(ppb)
Exp.Location
2005-2-18 Workshop for Underground experiments and astroparticle physics 21
Radon-Free techniques
Blocking Filtering Ventilation
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Radon Blocking capability for
various material
2005-2-18 Workshop for Underground experiments and astroparticle physics 23
Radon Blocking material :Example of KamLand
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Ventilation dependence of Radon
2005-2-18 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
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