Relation between gamma ray dose rate in air and whether

On increase of gamma ray dose rate in air during precipitation of rain and snow, the effects of amount of precipitation, wind direction and speed on the dose rate were investigated from 1997 to 2000. Six locations in Onagawa and Osika machi in Miyagi prefecture, Japan were selected. When it was rain, the distribution of dose rate shifted to higher dose rate, especially this phenomenon was observed in winter. The more precipitation intensity it was, the more decrease of dose rate. The effects of the wind direction and pressure distribution on increasing of gamma ray dose rate in air were not determined by the measurement results. The effects of the concentration of radon daughter nuclei in precipitation and route of atmospheric block on it were seemed to be larger than the above factors. (S.Y.)