DETERMINATION OF RADON USING SILICONE OIL SCINTILLATOR

Transcription

1 DETERMINATION OF RADON USING SILICONE OIL SCINTILLATOR Yukio Yoshizawa, Haruka Minowa and Makoto Takiue The Jikei University School of Medicine

2 Summary Silicone oil was used as a scintillation solven t to determine the radon concentration in w ater and air. Methyl phenyl silicone oil was thought to be an excellent scintillation solvent.

3 DETERMINATION OF RADON USIN G SILICONE OIL SCINTILLATOR a. Properties of radon. b. Liquid scintillation counting of radon. c. Features of silicone oil and its scintillator. d. Method for determination of radon in water. e. Method for determination of radon in air. f. Conclusion.

4 Properties of radon Radon is a radioactive noble gas, occurring n aturally as the decay product of radium. Radon gas emanates from soil, rocks, spring waters and hot springs.

5 Radon isotopes and progeny Radon α α β - α 222 Rn 218 Po 214 Pb 214 Bi 214 Po 210 Pb d 3.05 m 26.8 m 19.8 m 164 μs 22.3 y β - Thoron 212 Po 220 Rn 216 Po 212 Pb 212 Bi 208 Pb 55.6 s 0.15 s h m α β - stable Actinon α α α α 207 Tl 219 Rn 215 Po 211 Pb 211 Bi 207 Pb 3.96 s 1.78 ms 36.1 m 2.13 m β - stable β - β - β - α μs 208 Tl 3.05 m 4.77 m 210 Po s α β - α

6 Liquid scintillation counting of radon Liquid scintillation counting has been a s tandard measuring method for radon, esp ecially radon in water. This popularity is due to the high solubility of radon in organic solvents.

7 Integral counting method for determina tion of radon STUDY ON THE APPLICABILITY OF THE INTEGRAL COUNTING METHOD FOR THE DETERMINATION OF Ra IN VARIOUS SAMPLE FORMS USING A LIQUID SCINTILLATION COUNTE R Y. HOMMA and Y. MURAKAMI J Radioanalytical Chemistry. 36: (1977) Radon α α β - β - α 222 Rn 218 Po 214 Pb 214 Bi 214 Po 210 Pb d 3.05 m 26.8 m 19.8 m 164 μs 22.3 y

8 Integral counting method for determina tion of radon STUDY ON THE APPLICABILITY OF THE INTEGRAL COUNTING METHOD FOR THE DETERMINATION OF Ra IN VARIOUS SAMPLE FORMS USING A LIQUID SCINTILLATION COUNTE R Y. HOMMA and Y. MURAKAMI J Radioanalytical Chemistry. 36: (1977) Extraction of radon with toluene from water. Finding absolute counts by the integral counting method. The determination of 226 Ra was performed by counting the activity of 222 Rn with its descendants in a radioactive equilibrium.

9 Features of silicone oil Colorless transparent liquids. Physiologically inert. Resistance to heat, cold, and moisture. Soluble in organic solvents. Insoluble in water. CH3 CH3 CH3 CH3 Si O Si O Si O Si CH3 CH3 CH3 CH3 m n Formula of methyl phenyl silicone

10 Silicone diffusion pump oil HIVAC F-4 (Shin-etsu Chemical Co., Ltd.) CH3 CH3 Si O Si O Si CH3 CH3 Molecular weight Density 1.07 Burning point 210

11 Silicone oil scintillator cocktail 7 g of 2,5-diphenyloxazole (DOP) 0.2 g of 1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) 1 L of HIVAC F-4 T. Kato. Anal Chem. (1980)

12 Experiment ml each of scintillation cocktails was dispe nsed into the scintillation vials ml of radon-containing toluene was added to the each vial and mixed well. 3. Radon and progeny in equilibrium were meas ured for 100 minutes.

13 Scintillation Spectra from Radon 222 Rn Toluene scintillator Silicone scintillator 218 Po 214 Po

14 Method for determination of radon in water 1. Pour slowly one liter of sample water into a on e-liter bottle and then add 25 ml of toluene. 2. Shake vigorously for a minute. 3. Take 22 ml of toluene off and put into a vial. 4. Measure activity of radon and progeny using th e integral counting method. Mineral spring analysis method guide 2002 Ministry of the Environment, Government of Japan

15 Experiment ml of freshly prepared radon-containing water was po ured into a 50 ml centrifuge tube (60 ml of inner volume) and then 20 ml of scintillator was added. 2. The tube was shaken vigorously for 10 minutes. 3. After five minutes standing, solvent was separated from water ml of extraction solution was transferred to a vial and 7 ml of scintillator was added to the vial. 5. Two ml of original radon-water or extracted one was tran sferred to a vial and added 20 ml of Lumasafe plus. 6. Radon and progeny in equilibrium were measured using t he integral counting method for 100 minutes.

16 Radioactivity in scintillators and aqueous samples Activity (cpm) Aqueous Phase (Silic one Scintillator) Radon Water Toluene Scintillator Silicone Scin tillator Aqueous Phase (Tolue ne Scintillator) Time (day)

17 Method for determination of radon in air A NEW METHOD FOR THE DETERMINATION OF RADON IN S OIL AIR BY THE "OPEN VIAL AND INTEGRAL COUNTING WI TH A LIQUID SCINTILLATION COUNTER. K. HORIUCHI and Y. MURAKAMI J Radioanalytical Chemistry. 80: (1983) A: open vial holder B: wood stick C: filter paper D: paper disk E: polyethylene sheet F: soil

18 Experiment 3 1. A radon source was placed in a four liter of glass container. 2. Open counting vials containing 10 ml of liquid sc intillation cocktail were set in the container. 3. After 48 h, the open vials were sealed with caps a nd measured using the integral counting techniqu e.

19 Procedure blank of scintillators and PICO-RAD Sample Measure time Activity Activity Detection limit min counts cpm cpm PICO RAD Blank Toluene Blank Silicone Scintillator Blank

20 Radon trap ability of the open-vial method and PIC O-RAD system Sample Activity by extrapolati on Rn conc. by PICO RAD system Activity per unit concentration Counting st atistics of bl ank Detection li mit cpm Bq/m 3 cpm/(bq/m 3 ) cpm Bq/m 3 PICO RAD ± PICO RAD Silicone Scintil lator 1 Silicone Scintil lator Exposure time: 48 hours Errors are due to counting statistics (1σ).

21 Conclusion 1. The methyl phenyl silicone oil scintillator wa s applied to the radon samples. 2. The silicone oil was the excellent liquid scinti llation solvent. 3. There is a need for improvement of the comp osition of the scintillation cocktail. 4. Sensitivity of the radon determination method s using the silicone oil scintillator is sufficient for screening of indoor radon.