Pretreatment conditions for detecting <sup>134</sup>Cs -Eight years after the Fukushima Daiichi nuclear accident-

Abstract

134Cs is an activation product with a short half-life (2.06 years) that was released during the Fukushima Daiichi nuclear disaster. It is an important indicator of contamination from the disaster because it has been more than 30 years since the last event when 134Cs was released. The radioactivity ratio of 137Cs to 134Cs was approximately 1 at the time of the accident, and thus, it is possible to quantitatively evaluate the sources of 137Cs from the radioactivity of 134Cs in environmental samples. In particular, because the radioactivity of 134Cs in foodstuffs in Japan is low due to its short half-life, pretreatment (concentration) is essential for quantification. For analyses using a 2-L Marinelli vessel and a conventional HPGe semiconductor detector (relative efficiency 25%), the detection limit for 134Cs was approximately 0.05 Bq/kg without pretreatment. For the 137Cs contamination source segregation in Japan in March 2020, the radioactivity in samples must be at least 0.83 Bq/kg of 137Cs. This study provided guideline requirements for sample volume and pretreatment.