Variation of Radiation Dose in Tunnels

The inside of a tunnel was a semi-closed space, quite different from an outdoor environment, and had special environmental characteristics. In this study, we measured the radiation dose, dust, and wind speed for three tunnels (A, B, C), which penetrated the northern and southern regions in Kochi Prefecture, and attempted to specifically consider the factors for variations in the radiation dose. The results obtained showed that the radiation dose tended to be high inside the tunnel, but did not increase unilaterally away from the entrance. In addition to the radiation that came from soil to form mountains, it is believed that sediments present in leaked water and dust scattered in the air also contributed to this radiation source.