Size distribution of radioactive particles collected at Tokai, Japan 6 days after the nuclear accident

Airborne radioactive particles released by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in 2011 were collected with a cascade low-pressure impactor at the Japan Atomic Energy Agency (JAEA) in Tokai, Japan, 114 km south of the FDNPP. Size-fractionated samples were collected twice, in the periods of March 17–April 1, 2011, and May 9–13, 2011. These size-fractionated samplings were carried out in the earliest days at a short distance from the FDNPP. Radioactivity of short-lived nuclides (several ten days of half-life) was determined as well as 134Cs and 137Cs. The elemental composition of size-fractionated samples was also measured. In the first collection, the activity median aerodynamic diameter (AMAD) of 129mTe, 140Ba, 134Cs, 136Cs and 137Cs was 1.5–1.6 μm, while the diameter of 131I was 0.45 μm. The diameters of 134Cs and 137Cs in the second collection were expressed as three peaks at