Deposition of fission and activation products after the Fukushima Dai-ichi nuclear power plant accident

The Great Eastern Japan Earthquake on March 11, 2011, damaged reactor cooling systems at Fukushima Dai-ichi nuclear power plant. The subsequent venting operation and hydrogen explosion resulted in a large radioactive nuclide emission from reactor containers into the environment. Here, we collected environmental samples such as soil, plant species, and water on April 10, 2011, in front of the power plant main gate as well as 35 km away in Iitate village, and observed gamma-rays with a Ge(Li) semiconductor detector. We observed activation products (239Np and 59Fe) and fission products (131I, 134Cs (133Cs), 137Cs, 110mAg (109Ag), 132Te, 132I, 140Ba, 140La, 91Sr, 91Y, 95Zr, and 95Nb). 239Np is the parent nuclide of 239Pu; 59Fe are presumably activation products of 58Fe obtained by corrosion of cooling pipes. The results show that these activation and fission products, diffused within a month of the accident. ► We collected environmental samples near the Fukushima nuclear power plant. ► We observed 239Np and 59Fe along with many fission products. ► 239Np is evidently an activation product of 238U contained in nuclear fuel. ► 239Np is also parent nuclide of 239Pu. ► Our results show that activation products diffused within a month of the accident. We observed some activation product including 239Pu after the Fukushima Dai-ichi nuclear power plant accident.