【放射線科学】福島原発事故後のプルトニウム放出を示す証拠

As the one-year anniversary of the Fukushima nuclear disaster approaches, a study published in Scientific Reports this week presents isotopic evidence of the subsequent release into the atmosphere of plutonium and other radioactive elements. The results could prove important for estimating reactor damage at the Daiichi nuclear power plant (DNPP) and for the decontamination strategy. The magnitude-9.0 earthquake in Japan on 11 March 2011 caused serious damage to the electric system of the Fukushima DNPP. The accident triggered the massive release of radioactive elements into the environment but although evaluations have revealed the widespread distribution of highly volatile fission products, such as isotopes of caesium, the release of non-volatile radioactive elements, including certain plutonium isotopes, has remained uncertain. Plutonium isotopes, especially the short-lived plutonium-241 (241Pu), may present a large risk for internal radiation exposure via the ingestion of contaminated crops. Jian Zheng and colleagues assessed the composition of plutonium isotopes in surface soil and plant litter in the Fukushima region after the accident. They report isotope evidence for the release of plutonium into the atmosphere and on the ground in areas northwest and south of the Fukushima DNPP, including the 20-30 km exclusion zone. The high activity of 241Pu, compared to the more stable 239Pu and 240Pu, demonstrates the need for long-term assessment of radioactivity from both 241Pu and americium-241 into which it decays, the authors conclude.