Measurement of radiation and radioactivity in KEK Tsukuba-campus after Fukushima No. 1 Nuclear Power Plant accident

The radioactivity released by the Fukushima Daiichi No.1 Nuclear Plant accident was measured at the Tsukuba-campus of the High Energy Accelerator Research Organization (KEK). The Tsukuba-campus is located ~165 km south-southwest of the Fukushima nuclear plant. We set up several measurement points in the Tsukuba-campus and measured the time variation of the radiation dose over a year by using an NaI survey meter and an LaBr3 spectrometer. We measured the radioactivity concentrations in soils and dried grasses by using a germanium semiconductor detector with In-Situ Object Calibration Software (ISOCS). On April 1, 2011, the dose rate without a roof was ~50% higher than that with a roof owing to rain. With regard to the difference on the ground surface, on April 11, 2011, the dose rate on turf was 20% higher than that on tiles. However, since the end of May 2011, it became lower than that on tiles. On March 18, 2011, the radioactivity concentration of I in dried grasses and in soils was 109 and 0.8 Bq/g, respectively. On March 18, 2011, the radioactivity concentration of Cs and Cs in soils was 0.04 and 0.03 Bq/g, respectively; on April 1, 2011, the radioactivity concentration was 0.11 and 0.11 Bq/g, respectively.