Development of a live fish measuring method of ¹³⁷Cs concentration for masu salmon and white-spotted char inhabiting mountain streams in the difficult-to-return area in Fukushima Prefecture using a NaI (Tl) scintillation detector

We have developed a live fish measuring method of ¹³⁷Cs concentration for mountain stream fish, masu salmon and white spotted char, in the difficult-to-return area in Fukushima Prefecture using a 3x3 inch NaI (Tl) scintillation detector. The measurement using this equipment is convenient compared with more expensive Germanium semiconductor detector at investigation filed site or a base in neighborhood. By using individual identification markers, we succeeded in recording changes in the ¹³⁷Cs concentration of one same masu salmon. The accumulation rate of ¹³⁷Cs was estimated to be 24.7 Bq / kg / day in concentration and 2.1 Bq / day in ¹³⁷Cs amount in the two months from October 19 to December 20, 2020. On the other hand, it is necessary to consider the overestimation of ¹³⁷Cs concentration in small fish, the temperature condition of the detector, and the measurement error due to short-time measurement. (author)