ABSTRACT

We obtained the rare data on low activity concentration of ²⁴¹Am in the surface seawater collected at about 210 km northeast of Fukushima Daiichi Nuclear Power Plant (FDNPP) on 29 April 2011. The concentration of ²³⁶U, ²³⁸U, ²³⁹Pu, ²⁴⁰Pu, ¹³⁴Cs and ¹³⁷Cs in that seawater was also determined and the atomic ratio ²³⁶U/²³⁸U and ²⁴⁰Pu/²³⁹Pu was calculated. The activity concentration of 137Cs compared to that before the incident and the equal activity ratio of ¹³⁴Cs/¹³⁷Cs clearly indicate that the seawater was contaminated by the radioactive Cs discharged from the FDNPP, while the activity concentration of ²⁴¹Am as well as ²³⁶U, ²³⁹Pu and ²⁴⁰Pu was in the range of the values reported before the incident. ²⁴¹Am in the aerosols collected at about 120 km from the FDNPP, in which FDNPP derived ²³⁶U and Pu isotopes were found, was analyzed. However, no significant larger amount compared to ²³⁶U and ^239+240Pu was found.