A simple method of finding the percentage frequency that areas near a target will be affected by radioactive fallout of a critical dose is presented. The target location, the climatological period, the fission yield, and a critical dose or dose rate must be specified. If the distribution of the actual effective winds is not available, the assumption of a circular normal distribution of the effective wind is made. This distribution can be obtained by C. E. P. Brooks' method or, if the points are numerous as in describing an areal frequency pattern, by a mechanical method described herein.
1 Currently assigned to 10th Weather Group, APO 925, San Francisco, Calif.
