Measurement of the Radioactivity in Surface Soils
Surface soils have been collected since April 2011. Figure 10.2 shows a photograph of the soil sampling location. Soil samples were collected from a 30 × 30 cm2 area and a ground depth of 1 cm with a scoop at the center of the ground (Fig. 10.2). The collected soils were mixed and packed in U-8 sample cases at the sampling place. These samples were measured with a high pure germanium detector at Kinki University AERI in Osaka that was calibrated with a standard volume source, and the measured gamma spectrum was analyzed using the nuclide library of ORTEC EG&G. Measurement time was 1,800 s for each sample. The data include a summing effect correction and a self-shielding effect correction.
Fig. 10.1 Map of the research area in Fukushima City. Red line, research area for a dose rate measurement; blue point, sampling point of surface soils for a specific activity measurement
Fig. 10.2 Photograph of soil sampling point taken April 17, 2011. Soil samples were taken at the center of this ground
Dose Rate Distribution Survey
In this measurement, a GPS-linked NaI(Tl) scintillation counter  was used to simultaneously record the dose rates and location. The GPS-linked NaI(Tl) scintillation counter includes three components: the first component is the radiation detection unit, which uses a NaI(Tl) survey meter (TCS-171; Hitachi-Aloka Medical) and a microcomputer board (CQ-V850; ESP); the second component is the GPS receiver unit, which uses a USB-linked GPS receiver (UMGPS/MF; IODATA; GPS receiver chip, SiRF StarIII); and the last component is a data acquisition unit, an Ultra-Mobile PC (FM-V BIBLO LOOX U/ C30; Fujitsu). The radiation detection unit and the GPS receiver unit are linked to the data acquisition unit where dose rate and GPS data are saved. The data acquisition software was developed and built using the Visual C#/ .NET Framework (Microsoft).
The whole system was put in a portable bag with the detection head of the radiation detector positioned 50–60 cm above ground, and the measurement was taken while walking at a speed of about 100 m/min. The height of the radiation detector was determined from the limits of the detector equipment.
In the research area, there are some typical areas paved with different materials. Figure 10.3 shows a cushion paving area, Fig. 10.3b is a block paving area, and
Fig. 10.3 Sites for dose rate distribution measurement photographed July 17, 2011: cushion paving area (a), block paving area (b), and normal asphalt paving area (c). Dose rates were measured by walking at the center of the walkway
Fig. 10.3c is a normal asphalt paving area. Dose rates were measured with walking at the center of the walkway in the photographs.