Jonathan & Pooya Computational Neuroscience summer school June 17-29, 2007.
Presented by: S. M. Hosseini Pooya (PhD) National Radiation Protection Department
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Transcript of Presented by: S. M. Hosseini Pooya (PhD) National Radiation Protection Department
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Presented by: S. M. Hosseini Pooya (PhD)National Radiation Protection Department
Iran Nuclear Regulatory Authority
Development of a diffusion chamber for passive
discriminative measurements of
radon/thoron concentration in dwellings
F. Torabi Nabil, S. M. Hosseini Pooya, M. Taheri, M. Shamsaie Zafarghandi
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Introduction Radon (222Rn) has the most contribution in annually natural exposure of the human via inhalation of the gas. Thoron (220Rn) may have the same effects (even be more hazardous) due to the long lived of its daughters . As well most of the radon detectors are also sensitive to the thoron and may be affected on accurate measurements by the presence of thoron in media. Thus some of the researches are focused on the designing of discriminative systems for separated measurements of these isotopes. Most of the suggested systems have complicated designs (in active methods) and etching conditions (in passive methods). A home-made passive diffusion chamber which is based on SSNTD, has been used for many years for passive radon measurements in dwellings in Iran. In this research first the operation and calibration method of the chamber have been described for both radon and thoron measurements. Then the design is developed for separated measurements of radon/thoron, and the measurement characteristics of the detector are discussed in detail.
Structure of home-made diffusion chamber: for Radon measurements
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Electrochemical Etching (ECE) 4
H2O) 45% + C2H5OH 40% + KOH 15%Etchant PEW :Voltage:800 VFrequency: 2 kHzTime: 3 hrTemp.:25 ° C
0.0 0.5 1.0 1.5 2.0 2.5 3.00
25
50
75
100
Alpha Fluence: 1000 / cm2
Etchant: 15% KOH + 40% C2H
5OH + 45% H
2O
ECE Conditions: 32 kV.cm-1 , 2 kHz , 3 hr , 25oC
Alpha Particle Energy (MeV)
Det
ectio
n E
ffici
ency
(%)
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Calibration Method
The volume of calibration chamber for Radon is 50 litersand for Thoron is 4 liters
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0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000 Y=0.83186X
R2=0.90131
Trac
k de
nsity
(tr
acks
cm-2
)
Time-integrated thoron conc. (Bq lit-1 day)0 20 40 60 80 100 120 140 160 180
0
500
1000
1500
2000
2500 Y=13.54957X
R2=0.99989
Trac
k de
nsity
(tr
acks
cm-2
)
Time-integrated radon conc. (Bq lit-1 day)
S= 13.55 (Track.cm-2.Bq-1 .l .day-1) S= 0.83 (Track.cm-2.Bq-1 .l .day-1)
The calibration curve of the chamber for
Radon
The calibration curve of the chamber for
Thoron
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Results of the chamber response in the 4th International Intercomparison of Passive
Radon Detectors (by NIRS –Japan, 2011)
Home-Made Radon Diffusion Chamber
Reference values by NIRS Measured values by diffusion chamber
Activity Exposure time (h)
Rn conc. (Bq. m-3)
Int. Rn conc. (kBq.h.m-3)
Rn conc. (Bq. m-3)
Int. Rn conc. (kBq.h.m-3) Difference
Low 100 1022 ± 59 102 ± 6 1033.6 ± 70 103.36 ± 7.2 1%
Medium 50 8818 ± 221 441 ± 11 8409 ± 720 420.43 ± 36 4.60%
High 100 8753 ± 270 875.3 ± 27 8478 ± 760 847.88 ± 75 3.20%
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Developed diffusion chambers for discriminative measurement of radon and
thoron
A. Double-filter diffusion chamber & 212Po detector
B. Double-film diffusion chamber
Double-filter diffusion chamber + 212Po detector
Developed diffusion chamber: Radon detectorthe outside detector:
212Po detector
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Detector holder
Detector(Lexan 250µm)
Attenuator(Lexan 75µm)
• It attenuates only the particles of 8.78 MeV of 212Po to the energies between 0.5 to 1MeV and absorbs all of the other particles of the daughters.
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75% C2H4(NH2)2+25% H2O
attenuator The thickness of 75±2 μm has been calculated by Trim Code
The thickness of 75±2μm is achievable by soaking of the 250μm Lexan films in the Aqueous solution of Ethylenediamine for 4 hours at 25 ⃘C as :
Sensitivity of the diffusion chamber for radon measurements
The MDL values of the diffusion chamber for radon
measurements0 20 40 60 80 100 120 140 160
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Trac
k de
nsity
(trac
ks c
m-2)
Time-integrated radon conc. (Bq lit-1day)
0 5 10 15 20 25 300
2
4
6
8
Det
ectio
n Li
mit (B
q lit
-1)
Exposure time (day)
S= 8.95 (Track.cm-2.Bq-1 .l .day-1)
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tSC netTDMDL .
2
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Sensitivity of the outer Lexan film for 212Po measurements
0.0 0.1 0.2 0.3 0.4 0.50
1000
2000
3000
4000
5000
6000
Trac
k de
nsity
(trac
ks c
m-2
)
Exposure(Bq Lit-1 day)
S=7.96 (Track.cm-2.Bq-1 .m3 .day-1)
The MDL values of the outer Lexan film for 212Po
measurements
0 5 10 15 20 25 300.000
0.002
0.004
0.006
0.008
0.010
Det
ectio
n Li
mit
(Bq
lit-1
)Exposure time (day)
tSC netTDMDL .
2
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Calculation of Thoron Concentration The outer Lexan film only can measure the concentration of
212Po
Tn
Po
Tn F
CC
21264100913.0
CTn(Thoron concentration)can be calculated by:
The average value of FTn (Equilibrium Factor) is 0.03 in dwellings,
0.913 is the Equilibrium Coefficient,
100/64 is the reverse value of branching ratio in decay chain of 212Po
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Detector holder
Detector
Filter holder
Detector holder
DetectorFiber glass filter
Cap & fiber glass filter
Double-film diffusion chamber
The upper film detects Radon+ Thoron The lower film detects only the Radon
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0 5 10 15 20 25 300
10
20
30
40
50D
etec
tion
Lim
it (B
q lit
-1)
Exposure time (day)
upper film sensitivity=2.06
lower film sensitivity=1.60
S(upper film)=2.06S(lower film)=1.60
Sensitivity of the diffusion chamber for radon measurements
The MDL values of the diffusion chamber for radon
measurements
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0 1000 2000 3000 4000 5000 6000 7000 80000
100
200
300
400
upper film
Trac
k de
nsity
(tr
acks
cm
-2)
Time-integrated thoron conc. (Bq day lit-1)
0 5 10 15 20 25 300
200
400
600
800
1000
1200
1400
Det
ectio
n Li
mit
(Bq
lit-1
)Exposure time (day)
Sensitivity of the diffusion chamber for Thoron measurements
The MDL values of the diffusion chamber for Thoron measurements
S=0.056(Track.cm-2.Bq-1 .l.day-1)
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Conclusion
A home-made passive diffusion chamber which is based on Lexan SSNTD, has been developed for simultaneous measurements of radon/thoron in dwellings.
The sensitivity of the chamber shows that it is appropriate for seasonal measurements of radon in an extended range of concentrations.
The sensitivity of the double-film chamber shows that it is appropriate for seasonal measurements of thoron in areas with high thoron concentrations, while the double-filter method is appropriate for that of low concentration .
The advantages of the method are including its small size, light weight and simple etching process.
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Thank you!