Monitoring on the land
It is crucial for the evacuees to know to what extent they are compelled to be exposed to unwanted radiation when they return home. Upon request we carefully and closely measure radiation levels room by room per house, in a garden and the surrounding field. We report the results to a client with drawings in which each of measured points shows the accurate radiation level in the unit of micro Sieverts per hour (Sv/h).
When local people return home, as a way to know how much radiation one would be exposed to, we measure on request the radiation level in a room, a garden, and the surrounding field in view of their pattern of daily life. By mapping the levels in actual living environments, we can easily calculate the total amount of external exposure depending on where and how long they spend their time according to their weekly or monthly life pattern. This also helps them to avoid suspected places in which a possibility of internal exposure still remains.
We have high-precision measuring equipment, namely, an ionization chamber for the high radiation level up to 10 milli Sv/h, a NaI scintillation survey meter for the medium and low level down to 0.05 micro Sv/h, and others. For the detection of surface contamination, we use a β-γ coaxial GM type survey meter, which is newly developed by Electoronics Co., Ltd for this particular purpose. When it needs to differentiate the contribution of radioactive cesium which is the main radioactive element emitted from Fukushima Daiichi Nuclear Power Plant from that of natural elements such as 40K and 208Tl, a mobile γ-ray energy spectrometer, which is also developed by Electoronics Co., Ltd, is employed.
In our standardized monitoring procedure, we measure the radiation level at four corners and the center in a room at the height of 1 centimeter and at the height of 1 meter from the floor. We do near the ceiling above the center of the room. We quite cautiously trace and check on a berm around the house, gutter drain outlets, dried pool, path of rain water streams, and the surface of large garden stones. Even in areas already decontaminated by the central government, we frequently find so-called hot spots remaining here and there. We present the results in reports and charts.