Measurement of Radiostrontium with plastic scintillator using a …apsorc2017.org/file/PFile/A-194.pdf · 2017-10-11 · Chemical separation of radiostrontium using cation exchange

© 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

[email protected]

Measurement of Radiostrontium with plastic scintillator

using a liquid scintillation system

APSORC17 2017/9/17-22 at Jeju From Japan


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


1. Introduction What kind of department of Hitachi?

2

http://www.google.co.jp/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjJo5Oy6cbVAhWDEbwKHbb8CEQQjRwIBw&url=http://english.aimi-style.com/archives/812&psig=AFQjCNETML7UvUlyMHcF5dp1UttOWiuk4g&ust=1502253728662479


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.


Key features of a new measurement method

4


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


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.


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.


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.

© Hitachi, Ltd. 2017. All rights reserved. 9

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


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


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


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


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


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


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.


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..


Acknowledgements

17

We thank for the Tsukahara-SS Co., which had you offer a Kurukuru cutter.


Thank you for your attention!

Documents

Measurement of Radiostrontium with plastic scintillator using a …apsorc2017.org/file/PFile/A-194.pdf · 2017-10-11 · Chemical separation of radiostrontium using cation exchange