Measurements of regional distribution of radon-222 concentration

Outdoor 222Rn concentrations were measured with electrostatic integrating radon monitors (EIRM) at 40 points around Nagoya, in which 15 sets of 2-month-exposure data over 2.5 yr were obtained. Seasonal variation of 222Rn concentration showed a clear pattern which had a spring-to-summer minimum and an autumn-to-winter maximum. Annual means 222Rn concentration ranged 3.5∼11.7Bq·m-3 depending on locations. Higher concentrations were obtained in mountainous regions while lower concentrations were obtained near the sea. The relation between atmospheric 222Rn concentration and uranium content of granitic rocks was also discussed. High level 222Rn concentrations were obtained over areas of granitic rocks which were comparatively uranium-rich. As as almost linear relationship was recognized between the 222Rn concentration and exposure rate due to external natural radiation, a close correlation was anticipated between the concentration and 226Ra content of soil. From the obtained regional distribution of 222Rn concentration, per caput lung dose in the area was estimated to be about 0.44±0.11 mSv·yr-1. (author)