The Study for the Evaluation of the Method for 222 Rn in Water

Transcription

1 w y wz 9«( 2y) 134~138, 2006 J. of the Korean Society for Environmental Analysis 222 Rn Á Á Á½w Á Á»Á k w œ l The Study for the Evaluation of the Method for 222 Rn in Water Youngmi Oh, Jongbok Lee, Kyungjin Shin, Hakchul Kim, Jaehee Lee, Sanggi Jung, and Sangtae Lee Water Analysis and Research Center, Korea Water Resources Corporation, Daejeon , Korea The instrumentation used to count 222 Rn activity was liquid scintillation counter (LSC) which could resolute α and β radiations. The optimal scintillation liquid (High Efficiency Mineral Oil TM ) for Radon analysis was selected and the combination ratio for scintillation liquid and sample was founded as 1:1. Efficiencies and Spillover values were investigated for determining optimal Pulse Shape Discriminator (PSD) level for better discrimination between α and β radiations. The Minimum detectable activity (MDA) value was 0.04 Bq/L when the PSD level was 100. Samples were measured for 150 minutes using low diffusion polyethylene vessel and high Efficiency Mineral Oil TM. Key words: Radon, LSC, radiation 1. ƒ w ù m w ( 238 U, U) 235 m ( Th) 232 w z,, y». y eù» ƒ š wì 1) ƒ. s x, 1998 w w w 2) z(unscear) š» ü l vs œ l 52% w w s w. ù w w ƒ ƒ ³ w v. ƒ mw ww w öe. œ» w y» mw. mw. Tayyeb et al. 3) w w mw ƒ y mw j šw. d Ÿ» w, Ÿ» wš z, û» w ƒ yw» d š. w Ÿ» qx mw q k d ƒ w. q/ k w qx (pulse shape analysis, PSA) Ÿ ü q(α) l» xÿr (fluorescence pulse)ƒ k(β) w xÿr ¼ ƒ w w Ÿ qx mw q vj k w x k z. 222 Rn w Ÿ, Ÿ To whom correspondence should be addressed. esangtae@hanmail.net

2 222 Rn 135 w v, PSA w Ÿ» w ü 222 Rn y w Rn t w 226 Ra t (0.2 µci, ISOTOPE PRODUCTS LABORATORIES, USA) w, Ÿ Perkin Elmer High Efficiency Mineral Oil TM, Hi-Safe III TM, Ultima gold AB TM, Ultima gold LLT TM w x» d w q k w r w qx» ƒ Packard Tri- Carb 3170 TR/SL Ÿ» w t 222 Rn t 226 Ra t (373 Bq/mL) 10 ml ƒ ¼»(scintilation vial) š ƒ k» g w» w z Ÿ (High Efficiency Mineral OilTM) 10 ml ƒw w. k x w 10 ml Ÿ 10 ml w w. mw» yw» w» ü lv gq 20 ml s p» w.» xÿ w d p g. qx (PSA) d t 226 Ra t Ÿ High Efficiency Mineral Scintillator ƒƒ TM 10 ml w 20 ml» 25 ew v w ƒ g w x Ÿ Ÿ w q 4ƒ Ÿ vj e,, w Ÿ yw yw wš Ÿ yw k y w qx (PSA) t ƒ š PSA q rp k rp q d z y w d z d ƒƒ 226 Ra t d w t y y wš w d z w ww L.Curie(1968) w w 15,16) wwe w. 3. š 3.1. Ÿ Ÿ Fig. 1 x zw š ƒ q Ÿ w w k x w. Ÿ Perkin Elmer High Efficiency Mineral Oil TM, Hi-Safe III TM, Ultima gold AB TM, Ultima gold LLT TM 4. Ÿ l» Ÿ, 4 Ÿ x Fig. 1. Test result according different kinds of scintillators.

3 136 Á Á Á½w Á Á»Á k Fig. 2. Test for optimal mixing ratio of sample & scintillator. High Efficiency Mineral Oil w TM vj eƒ w Po Ÿ w y 218 w Ÿ yw Ÿ v (10/10) yw wš 20 ml w 5~15 ml¾ 5 w k d w (Fig. 2). š q w d w k ƒ yw š w. x : Rn yw 222 1:1 ƒ w k ùkù 1:1 yw w qx (PSA) qx (PSA) 226 Ra t Ÿ yww 25 ew t ƒ š PSA 0~240¾ 18 w ƒ PSA q rp k rp (spillover(%)) d w. Fig. 3 q PSA 0~100 yƒ ƒ z w w yw ùkù 170 l. ù spillover(%) 90 ƒw» w 170 l ùkü. x k PSA q w q Fig. 3. Determination of PSA. spillover(%) ƒw» w š 100 w. PSA 100 w k ƒ q š, 100 q ƒ k z ƒ d z d PSA 222 Rn q w w s³ d z w» w 226 Ra t w 1.49~29.84 Bq 226 Ra w z 1 ew. z ƒ t w q vj d w.» d z Ÿ w 222 Rn z d» dz sww. Fig. 4 x t q vj w Ra 226 Fig. 4. Calibration curve of the 226 Ra standard sample solutions in low-diffusion polyethylene vial with different activity, ingrowth period of 29 days.

4 222 Rn 137 (Bq)ƒ x ew. d z (ε) z e Ra sx š w 226 F. A. Hohorst (1995) w 14) w. CPM A CPM B E = A S ( 1 exp λ T ) 60», λ : 222 Rn (0.182/ ) T : l d ¾ ( ) As : 226 Ra t (Bq) CPM A : q vj (CPM) CPM B : q vj (CPM) q vj w s³ d z PSA % ùkû ww (Minimum Detectable Activity, MDA) x d 1000 wš œ x w 5z d w. wwe(mda) L. Currie(1968) 15,16) w w. MDA Bq L ( ) 4.65 C B = V 60 t», C B : (CPM) V: (L) t: d ( ) = d ( ) ε : q vj d z 5z e œ d s³ (C B ) L d 1,000.» w q d z 2.55 L. Currie(1968) w w Bq/L MDA w. 4. Ÿ» w w Rn d 222 w. Ÿ» q k ƒ ƒ w Packard Tricarb 3170-TR w. Ÿ 4 Ÿ x High Efficiency Mineral Oil TM (Perkin Elmer, U.S.A.) w 218 Po Ÿ w y wš ƒ š» ƒ» mw d z ùkü j w w q Ÿ w, Ÿ yw 1:1 w. PSD dw wwe(mda) 0.04 Bq/L š, 226 Ra t w 226 Ra t w 222 Rn w, 218 Po, 214 Po d z 255% ù kû. š x 1. N. Harley, J.M. Samet, F.T. Cross, T. Hess, J. Muller, D. Thomas, Health Perspect., 1986, 70, NAS, 1999, Risk assessment of radon in drinking water, National Academy Press. Washington, D. C. 3. Z.A. Tayyeb, A.R. Kinsara, S.M. Fraid, J. Env. Radia., 1998, 38, APHA, AWWA, WEF, Standard methods 7500-Rn. 5. ASTM D : Standard test method for Radon in drinking water. 6. x,, y, x, yÿ,, Analytical Science & Technology, 1999, 12, Barnett, J.M., McKlveen J.W., J. Radioanal. Nucl. Chem. Art., 1992, 161, Schonhofer, F. and Henrich E., J. Radioanal. Nucl. Chem. Art., 1987, 115, Schonhofer, F. and Henrich, E., J. Radioanal. Nucl. Chem. Art., 1992, 45, Chereji, L., J. Radioanal. Nucl. Chem. Lett., 1992, 165, Cooper, E.L., Brown, R.M., and Milton, G.M., EnvironInt., 1998, 14, Gomez Escobar, V., Vera Tome, F., and Lozano, J.C., Radia. Isot., 1996, 47, Dillon, M.E. Carter, G.L., Arora, R., and Kahn, B., J.

5 138 Á Á Á½w Á Á»Á k Health Physics., 1991, 60(2), F. A. Hohorst, M. W. Huntley, and S. D. Hantenstein, INEL-95/0546, L. Currie, Anal. Chem., 1968, 40, B.S. Pastermnack and N. H. Harleg, Nucl. Instrum. Methods, 1971, 91, K. Treutler, H. C., Dehnert, J., and Nestler, W., J. Env. Radia., 1997, 37,