Figure 3 : Curves of the calculated activity ratios of 241Pu/239+240Pu and 241Am/239+240Pu from the Nagasaki atomic bomb Pu, the global fallout Pu and the Fukushima DNPP accident Pu with elapsed time.

From: Isotopic evidence of plutonium release into the environment from the Fukushima DNPP accident

Figure 3

The 241Am ingrowth from the Nagasaki atomic bomb detonation was based on the initial 241Pu/239+240Pu activity ratio estimated by Yamamoto et al.27. The 241Am/239+240Pu activity ratio (0.036 ±0.006) detected in a soil core collected in Nishiyama area, Nagasaki, Japan in 2008 approached the calculated maximum value, indicating that 241Am and Pu were still together in the soils after 6 decades. 241Am from the global fallout source was expected to reach the maximum 241Am/239+240Pu activity ratio of 0.36 in the year 204225. The theoretic calculation indicated that 241Am/239+240Pu activity ratio would quickly approach the value of 1 by 7 years after the Fukushima DNPP accident and it would reach a maximum value of 3.18 in the year 2081.