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Minimum Detectable Activity(MDA) for Analysis of Noble Gas in Atmosphere It is important to determine whether radioactivity of noble gas in atmosphere exist or not. It is also difficult to know the real value due to radioactivity or the fluctuation of background, specially among ultra low background counting sample such as noble gas analysis in atmosphere. This report has following contents: Introduction of the general MDA Method of MDA calculation for noble gas analysis The reduction method of MDA The MDA value has been estimated in radioactivity analysis of noble gas in atmosphere. It is proposed how to reduce MDA in ultra low background sample and introduced several type of MDA used in the field. The minimum MDA value for total xenon is 0.4 mbq/m 3 and the range of MDA value is almost below 1 mbq/m 3. This - iv -
factor is lower than that value proposed from the company of Germany. Here the MDA of 85 Kr is proposed and the minimum time is determined. The MDA value has been introduced in radioactivity analysis of noble gas in atmosphere and it has been calculated. It is applied in how to determine the singular value of radioactivity for noble gas or not. - v -
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표 2-1 미국 LLNL 주변에서는 Cs 와 Pu 의측정값 ( 참고 : LLNL 보고서 ) - 3 -
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그림 3-1 측정된시료의계수에따라서검출한계판단영역세가지 그림 2-2 Currie 논문에서정의한 LLD 개념 - 5 -
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표 2-2 검출한계유도와관련된양 ( 단위 : 계수 ) 참평균측정평균표준편차 Blank( 블랭크신호 ) 총신호 (total signal) 순신호 ( Net signal) 백그라운드신호 (Back ground) 1회측정 N회측정 - 7 -
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표 2-3 LLD 설정을위한오차및그에대응하는, 값들, 10 % 5 % 2.5 % 1.0 % 0.5 % 0.1 %, 1.282 1.645 1.960 2.326 2.576 3.090-10 -
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표 2-4 감마핵종분석에서의 MDA 종류에따른값의변화 - 12 -
표 2-5 LLD 와 MDA 에차이점 - 13 -
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Curie( 측정시간같음 ), 유의수준 =95 % mbq/m 3 1.20 1.00 0.80 0.60 0.40 0.20 0.00 40000 90000 140000 190000 Time (sec) BG(=1 cmp) BG(=2 cpm) Bg(=3 cpm) 그림 3-1 측정시간이같을때백그라운드 cpm 에따른 MDA 변화 - 15 -
Currie( 측정시간다름 ), 유의수준 =95 % mbq/m 3 1.20 1.00 0.80 0.60 0.40 0.20 0.00 40000 90000 140000 190000 Time (sec) BG(=1 cmp) BG(=2 cpm) BG(=3 cpm) 그림 3-2 측정시간다를경우 MDA 변화량 - 16 -
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독일 DIN( 측정시간다름 ), 유의수준 =95 % mbq/m 3 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 40000 90000 140000 190000 Time (sec) BG(=1 cmp) BG(=2 cpm) Bg(=3 cpm) 그림 3-3 측정시간다를경우유의수준 95 % 일경우 MDA 독일 DIN( 측정시간다름 ),1 종과오 (5%), 2 종과오 (0.1%) mbq/m 3 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 40000 90000 140000 190000 Time (sec) BG(=1 cmp) BG(=2 cpm) Bg(=3 cpm) 그림 3-4 측정시간다를경우제 1 종과오 5 % 및 2 종과오 0.1 % 로했을경우 MDA - 18 -
MDA 구하는 방법 표 3-1 유도식에따라시간에따른 MDA 값의변화 DIN Currie 식에서 Currie 식에서 DIN 제1종과오과오 95 t_b=t_m이같음 t_b,t_m이다름제1,2종과오 95 % %, 제 2종과오제1,2종과오 95 % 제1,2종과오 95 % 99.99 % 1 2 3 4 t_m(h) t_s 1 2 3 1 2 3 1 2 3 1 2 3 14 50400 0.66 0.93 1.13 0.58 0.82 1.00 0.49 0.68 0.83 0.89 1.24 1.51 16 57600 0.62 0.87 1.06 0.55 0.78 0.95 0.47 0.65 0.79 0.85 1.19 1.45 18 64800 0.58 0.82 1.00 0.53 0.75 0.92 0.45 0.63 0.76 0.82 1.15 1.40 20 72000 0.55 0.77 0.95 0.52 0.73 0.89 0.43 0.61 0.74 0.80 1.11 1.35 22 79200 0.52 0.74 0.90 0.50 0.71 0.87 0.42 0.59 0.72 0.77 1.08 1.32 24 86400 0.50 0.71 0.86 0.49 0.69 0.85 0.41 0.58 0.70 0.76 1.06 1.29 26 93600 0.48 0.68 0.83 0.48 0.68 0.83 0.40 0.57 0.69 0.74 1.03 1.26 28 100800 0.46 0.65 0.80 0.47 0.67 0.81 0.40 0.56 0.68 0.73 1.02 1.24 30 108000 0.45 0.63 0.77 0.46 0.65 0.80 0.39 0.55 0.67 0.71 1.00 1.22 32 115200 0.43 0.61 0.75 0.46 0.64 0.79 0.38 0.54 0.66 0.70 0.98 1.20 34 122400 0.42 0.59 0.72 0.45 0.64 0.78 0.38 0.53 0.65 0.69 0.97 1.18 36 129600 0.41 0.57 0.70 0.45 0.63 0.77 0.37 0.52 0.64 0.68 0.96 1.17 38 136800 0.40 0.56 0.68 0.44 0.62 0.76 0.37 0.52 0.63 0.68 0.95 1.15 40 144000 0.39 0.55 0.67 0.44 0.61 0.75 0.37 0.51 0.63 0.67 0.94 1.14 42 151200 0.38 0.53 0.65 0.43 0.61 0.74 0.36 0.51 0.62 0.66 0.93 1.13 44 158400 0.37 0.52 0.64 0.43 0.60 0.74 0.36 0.50 0.61 0.66 0.92 1.12 46 165600 0.36 0.51 0.62 0.42 0.60 0.73 0.36 0.50 0.61 0.65 0.91 1.11 48 172800 0.35 0.50 0.61 0.42 0.59 0.73 0.35 0.50 0.60 0.65 0.91 1.10 50 180000 0.35 0.49 0.60 0.42 0.59 0.72 0.35 0.49 0.60 0.64 0.90 1.10 52 187200 0.34 0.48 0.58 0.41 0.58 0.72 0.35 0.49 0.60 0.64 0.89 1.09-19 -
1.60 Xe MDC due to BG count rate 1.40 MDA(mbq/m 3 ) 1.20 1.00 0.80 0.60 0.40 Xe 0.20 0.00 0 2 4 6 8 10 Background count rate(cpm) 그림 3-5 백그라운드계수율에따른 MDA 변화 - 20 -
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100.00 Currie( 측정시간같음 ), 유의수준 =95 % BG(=1 cmp) mbq/m 3 10.00 BG(=2 cpm) BG(=3 cpm) 720 sec 1260 sec 1800 sec 1.00 0 500 1000 1500 2000 Time (sec) 그림 3-6 백그라운드계수율에따른 MDA 변화 - 22 -
100.00 Currie( 측정시간같음 ), 유의수준 =95 % 10.00 BG(=1 cmp) mbq/m 3 BG(=2 cpm) BG(=3 cpm) 1.00 0.10 0 20000 40000 60000 80000 Time (sec) 그림 3-7 시간에따른 MDA 변화 ( 백그라운드계수율 : 1, 2, 3 cpm) - 23 -
14.00 12.00 Kr MDA due to BG count rate Kr 10.00 MDA(mbq/m 3 ) 8.00 6.00 4.00 2.00 0.00 0 50 100 150 200 250 Background count rate(cpm) 그림 3-8 백그라운드계수율에따른 MDA 변화 - 24 -
90.00 Kr MDA due to air collection volume of air 80.00 MDA(mbq/m 3 ) 70.00 60.00 50.00 40.00 30.00 20.00 Kr 10.00 0.00 0 2 4 6 8 10 12 collection volume(m 3 ) 그림 3-9 공기포집량에따른 MDA 변화 - 25 -
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그림 3-10. Decay correction method of Xe measurement among Atmosphere - 27 -
최소 최대 포집량 (cc) 0.35 0.6 효율 (%) 70 90 MDA (mbq/m 3 ) 1.04 0.47-28 -
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[1] L.A Currie, "Limits for qualitative detection and quantitative determination ", Anal. chem., 40(30), pp. 586-593, 1968. 이재기, 환경방사능감시 : 워크숍환경방사능검출한계에대한고찰 한국원자력안전 기술원, 1996. 한국원자력연구원, 금동권외다수, 대기중 Kr-85 분석기술개발, 2004. 이명호외다수, 환경시료중 Pu 측정에서최소검출방사능농도산출에대한연구 분석과학회지, vol. 14. No.1, 2001. 한국원자력안전기술원, 계측통계, 2000. 한국원자력안전기술원, KINS/G-009, 방사능표준분석법, 감마핵종분석법. 이완로외다수, 공기중방사성제논측정에서최소검출농도 (MDA) 산출에관한연 구, 2010 한국방사성폐기물학회춘계학술대회 - 31 -
한국원자력연구원, 이완로외다수, 대기중제논및크립톤포집기술, KAERI/TR-4087/2010, 2010. - 32 -
In Jun The MDA value has been estimated in radioactivity analysis of noble gas in atmosphere. It is proposed how to reduce MDA in ultra low background sample and introduced several type of MDA used in the field. The minimum MDA value for total xenon is 0.4 mbq/m 3 and the range of MDA value is almost below 1 mbq/m 3. This factor is lower than that value proposed from the company of Germany. Here the MDA of 85 Kr is proposed and the minimum time is determined.