The distribution of terrestrial gamma-ray dose rates in Nagoya city

This study investigated whether variations in dose rates exist in a small area such as Nagoya, and accurate dose rates were measured in relation to geological features. Gamma rays were measured with a NaI(Tl) scintillation counter. In order to assess the influence of soil brought from other places on the results of this investigation, radiation at various sites (temples, school grounds, parks, river beaches, etc.) was measured first. Based on the result, parks were selected as the measurement site, and dose rates were measured at 268 parks. The arithmetic mean of the measured value was 45.9 nGy/h, and the standard deviation was 7.1. A contour line map of terrestrial gamma-ray dose rates was made for the entire area of Nagoya, and the dose rates distributions were compared with outer layer geological features. By carefully selecting the measuring conditions and sites, accurate gamma dose rates were measured in Nagoya. The influence of the mixed soil also appeared to have been minimized, because the dose distribution corresponded very closely to the geological features, and the form of the power spectra was natural, but the influence could not evaluated quantitatively. (K.H.)