Observation of -rays from fallout collected at Ibaraki, Japan, during the Fukushima nuclear accident

Saegusa, Jun; Kikuta, Yasuaki; Akino, Hitoshi

Measurements of -ray pulse height distributions were performed for a fallout sample collected at Ibaraki, Japan during the Fukushima accident in March, 2011. The fallout was collected in a pan of water, then evaporated to dryness on a stainless-steel holder. The sample was measured by a germanium detector three times over a year. In the pulse height distribution of the initial measurement, approximately 140 peaks were observed between 50 and 2048 keV energy region. Most of them were either total absorption peak or the sum peak of Te, I or Cs isotopes. Compared to the fallout sampled at the past nuclear accidents, while some nuclides such as Ce and Ru were not detected, Ag etc was prominently observed. Radioactivity concentration of Cs was estimated to be at least 1.410 Bq m, approximately 14% of which was attributed to rainout.