NaI (Tl) スペクトロメトリーによる牛乳中放射性ヨウ素定量法の誤差評価

抄録

An uncertainty in the method of determination of radioactive iodine (¹³¹I) in milk with a NaI (Tl) scintillation spectrometry of which procedure manual is provided by the Science and Technology Agency is analyzed on the basis of a train of the actually measured data, and a minimum detectable activity in a routine monitoring is estimated. Judging from the error analysis, the total systematic error of the concentration of ¹³¹I in milk is about 10pCi/l, which is mainly attributed to the presence of natural radioactive nuclides except ⁴⁰K, and the total random error is ±6 pCi/l resulting from the counting error and the deviation in gain adjustment. If we define a minimum detectable activity as the sum of systematic error and three times random error, it would be about 30pCi/l for ¹³¹I, But in case some other unexpected nuclides are contained in milk, this method cannot afford to determine the concentrations precisely.