measurement of radiostrontium with plastic scintillator using a...
TRANSCRIPT
© Hitachi, Ltd. 2017. All rights reserved.
1)Hitachi, Ltd. 2)The Jikei University School of Medicine 3)Nagoya University
1Yuka Kato, 2Haruka Minowa and 3Yoshimune Ogata
Measurement of Radiostrontium with plastic scintillator
using a liquid scintillation system
APSORC17 2017/9/17-22 at Jeju From Japan
© Hitachi, Ltd. 2017. All rights reserved.
1. Introduction 2. Measurement method 3. Results and discussion 4. Conclusion
Contents
1
What kind of department of Hitachi? Background and purpose
Key features of a new measurement method Measurement samples
Result of a measurement of each sample
© Hitachi, Ltd. 2017. All rights reserved.
1. Introduction What kind of department of Hitachi?
2
© Hitachi, Ltd. 2017. All rights reserved.
Background and purpose
3
Conventional methods for analyzing radioactive strontium are:
Time-consuming complicated procedures with deleterious substances.
When liquid scintillation counting method is adopted, organic liquid waste is generated.
We tried to develop a simple, quick and safety analysis method of radioactive strontium in seawater.
Chemical separation of radiostrontium using cation exchange method. Sr is collected by carbonate precipitation on a filter. Details of the chemical separation procedure were explained by Dr.
Minowa on Tuesday.
In this presentation, a new measurement method using plastic scintillator.
© Hitachi, Ltd. 2017. All rights reserved.
Key features of a new measurement method
4
© Hitachi, Ltd. 2017. All rights reserved.
Using the Plastic scintillator
5
Parts Materials Plastic scintillator EJ-200, Eljen Technology, 47 mmφ × 15 mm Spacer PC, Hitachi, Ltd. 44 mmφ × 22.5 mm Sealed film PE, Commercial products,200 µm 145 mL bottle PORYVIALSR 145, Zinsser Analytic GmbH
Plastic scintillator bottle
145 mL bottle
Sealed filter
Plastic scintillator
Spacer
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Low background liquid scintillation system
6
AccuFLEX LSC-LB7, Hitachi, Ltd.)
LSC-LB7 Cosmic rays are eliminated by an anti-
coincidence circuit. The large capacity bottle can be counted
with high efficiency by using three PMTs. Sample on a membrane filter can be
measured using the plastic scintillation bottle and LSC-LB7.
© Hitachi, Ltd. 2017. All rights reserved.
Measurement samples
7
Sample name Sample Filter Method Instruments
STD1 Spiked 90Sr standard solution Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
STD2 Spiked 90Sr standard solution - Liquid scintillator LSC-7400
LIN1-8 Spiked 90Sr standard solution Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
APR1-4 Spiked 90Sr standard solution Membrane filter 25 mmφ Plastic scintillator Liquid scintillator
LSC-LB7 LSC-7400**
SEA1 Artificial seawater + 90Sr (Cation exchange method) Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
SEA2 Natural seawater + 90Sr (Cation exchange method) Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
SEA3 Natural seawater + 90Sr (Cation exchange method) Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
BKG1-7 ) Membrane filter 45 mmφ* Plastic scintillator LSC-LB7
* Cut it from 47 mmφ using a Kurukru cutter (Kurukru cutter is made by Tsukahara-SS, Co.) ** LSC-7400 (AccuFLEX LSC-7400, Hitachi, Ltd.) is a general purpose type.
© Hitachi, Ltd. 2017. All rights reserved.
Effect of using plastic scintillator bottle
8
Cou
nts
Energy (keV) Energy (keV)
90Sr 90Sr
90Y 90Y
Plastic scintillator bottle (LSC-LB7) This sample is 90Sr standard sample. The spectrum of 90Sr shows a
maximum energy around 546 keV. The spectrum of 90Y exceeds 2000 keV.
(90Y: 2280 keV)
Liquid scintillator (LSC-7400) This sample is 90Sr standard
sample. Both 90Sr and 90Y are affected by
chemical quenching, the spectrum shifts to the low energy side and does not show the maximum value.
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Variation of the 90Sr standard samples
Average
Average+1%
Average-1%
Measurement with LSC-LB7 The STD1 sample was using the plastic scintillator bottle. The variation of 300 times of measurement was less than 1%.
STD1
Conditions Measurement times : 10 min, Measurement window : 5-2000 keV, Number of measurements : 300
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90Sr-90Y linearity of measurements
10
Sample No. Bq Net-CPM Efficiency
LIN1 0.405 34.87± 0.71 72% LIN2 0.691 56.60± 0.74 68) LIN3 1.742 144.2± 1.03 69% LIN4 4.087 364.0± 1.95 74) LIN5 5.584 422.5± 1.83 63) LIN6 11.17 849.3± 2.58 63) LIN7 24.47 2020± 3.68 69) LIN8 45.57 3662± 6.07 67)
Conditions Measurement times : 100 min-150min Measurement window : 5-2000 keV
Measurement with LSC-LB7 The LIN samples measured it
using the plastic scintillator bottle. The result showed good linearity. R2 = 0.9994
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Comparison with 90Sr standard sample
11
Samples Plastic scintillator bottle (LSC-LB7)
Liquid scintillator (LSC-7400)
Sample No. Activity(Bq) Counts(min-1) Efficiency(%) Counts(min-1) Efficiency(%)
APR1 880 37874 71.7 49271 93.3 APR2 837 35874 71.4 47934 95.4 APR3 866 36114 69.5 49185 94.7
Filter sample preparation 20 μL of 90Sr standard solution was dropped on a membrane filter (Millipore, 25 mmϕ) and dried.
Measurement with LSC-LB7 Each filter was sandwiched in polyethylene film, placed in the plastic scintillator bottle, then measured with LSC-LB7.
Measurement with LSC-7400 Each filter was put into 20 mL vials, 20 mL of liquid scintillator (Clearsol-2) was added, then measured with LSC-7400.
Conditions Measurement times : 10 min, Measurement window : 0.5-2000 keV
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Separation method of strontium from seawater
[First solution] (Spiked radiostrontium to seawater)
Cation exchange Column
Dowwx50W-X8 50-100 mesh
[Rinse] [Elution]
through out solution rinse solution eluate
Heat 80℃, 1h
pH>9, NaCO3
Leave to cool, 1 night
[Filtration]
precipitate
supernatant
Dry
[Sealed]
Radioactivity counting
Plastic scintillator bottle Cut the filter with
“Kurukuru cutter”.
Sample preparation method of SEA1-3
12
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90Y Growth curve
13
90Sr 90Y 90Zr (Stable)
Nuclide Half-life βmax (MeV)
90Sr 28.79) 0.546
90Y 64) 2.280
Measurement with LSC-LB7 The SEA samples were using the plastic scintillator bottle. Growth curves of SEA1-3 were in good agreement.
Conditions Measurement times : 1 min or 10 min Measurement window : 5-2000 keV
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Dispersion of the background samples
14
Measurement with LSC-LB7 The BKG samples were using the plastic scintillator bottle. The error range used 3 times of the standard deviation. The average was 8.1 cpm, and the difference from the average was
up to 0.6 cpm.
Conditions Measurement times : 10 min, Measurement window : 3-2000 keV, Number of measurements : 30
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The minimum detectable concentration (MDC)
15
t : Measurement time (min) ε : Apparent efficiency Y : Chemical yield nDL : Detection limit of count rate (cpm) ADL : Detection limit of activity (Bq) nb : Background count rate (cpm) V : Sample volume
Calculation condition Chemical yield : 70% Counting efficiency : 70% Back ground : 8.1 cpm Measurement time : 60 min Sample volume : 200 mL
MDC = 𝐴𝐴𝐷𝐷𝐷𝐷1000𝑉𝑉
0.1Bq L-1
MDC with LSC-LB7 The MDC becomes the high value
because there is much volume of sample.
In the case of 1000 mL of sea water, MDC will be 0.02 Bq L-1.
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Conclusions
16
Since this method is not affected by chemical quenching, quenching correction curve is not needed.
Since the variation in repeated measurements of the background sample (BKG) and the standard sample (STD) was small, and the linearity was also good, therefore the measurement accuracy of the plastic scintillator was confirmed.
Although the counting efficiency in a plastic scintillator bottle is about 70%, MDC is good because a large amount of sample can be measured. The MDC is 0.02 Bq L-1 when the sample is 1 L, which is sufficient to estimate the radioactive strontium concentration in the environmental sample.
The plastic scintillator bottle method have quantitative favorably compared with liquid scintillator method.
Since the filter is sealed with polyethylene film, the plastic scintillator is free from contamination. So that it is reusable. Furthermore, no organic liquid waste is generated.
This method can be used another method to collect strontium by means of solid phase extraction disk (EmporeTM Strontium RadDisk, 3M).
The new counting method using the plastic scintillation bottle can be applied to measure other beta nuclides emitting relative high energy beta-rays, such as 32P, etc..
© Hitachi, Ltd. 2017. All rights reserved.
Acknowledgements
17
We thank for the Tsukahara-SS Co., which had you offer a Kurukuru cutter.
© Hitachi, Ltd. 2017. All rights reserved.
Thank you for your attention!