2013 Volume 42 Issue 1 Pages 20-30
Radiation contamination by Fukushima accident in Kashiwa campus of University of Tokyo, which is located in the northwestern part of Chiba prefecture, was surveyed and decontamination methods were tested in nursery lawn in the campus. In open space and forests in the campus, air dose rate at 1 m aboveground was 0.3–0.6 μSv/h, and soil radiation was 39–137 kBq/m2 in the campus green. From vertical profiles of the pollution in lawn soils, radioactive cesium was found to be concentrated in the 0–1 cm layer of the surface soil and the amount of cesium in the clay particles (35–107 kBq/m2) was significantly greater than cesium amount in turf leaves, roots and thatch. Decontamination by mowing the turf and vacuuming up the thatch with a reel mower and a rotary mower (A-method) was not effective, while stripping the turf and surface soil layer with a sod cutter (B-method) decreased the air dose satisfactory from 0.4–0.6 μSv/h to 0.11–0.21 μSv/h at 5cm aboveground. Around the drain of roof gutter, soil pollution was higher than 100 kBq/kg at the surface 2 cm layer and more than 10 kBq/kg at 4–6 cm depth, and soil replacement to 6 cm deep reduced the air dose rate at 5 cm aboveground only to 0.5 μSv/h.
