A method of numerical calculation of the γ-dose rate from the radioactive cloud was devised under the supposition that the distribution of the cloud is uniform along the flow direction; the relative error due to the supposition is less than 5%.
This method is capable of acquiring more accurate values than by the other calculations under the assumptions like the circle-like cross-wind section of the cloud and/or the neglecting of the build-up phenomena.
Actual calculations were made graphically to save time and effort efficiently. As the result of this method, the γ-dose rate distributions for the fission products cloud and the 41A cloud were obtained. This method of estimating γ-dose rate distributions was verified by the experiments using 41A cloud dispersion (at JAERI, in 1961).