Radioactivity and Air Dose Rate
ＱHow is radioactive Cs distributed in a town?
ＡOur evaluation showed that the amount of radioactive Cs remaining on planar permeable fields was large, whereas that on paved grounds or buildings was small.
Those figures present the percentages of inventories relative to the values of the inventories on planar permeable fields measured in 2015 and converted to those immediately after the accident. The relative inventories four years after the accident were significantly low on paved ground and on building surface materials in the evacuation zone in which decontamination had not been conducted. These results indicate that large amounts of radioactive Cs deposited in residential areas were removed by the initial runoff and subsequent wash-off effects of rainfall, even without decontamination.
Porous materials such as mortar showed significantly higher relative 137Cs inventories than others; smooth-surface materials such as glazed tile and metallic slate showed obviously smaller values. This indicates that 137Cs deposited on smooth-surface materials are easily and quickly removed from the surface.