The influence of the wind structure at various altitudes on the ground distribution of the nearby fallout is qualitatively repre- sented in Figure 2. The last sketch in Figure 2 illustrates the effects of the "shearing" action of the winds when they travel in different _ directions and/or speeds at the various altitudes through which the particles must fall. Due to these wind conditions, it is possible to obtain fallout patterns ranging from one looking like an ink blot around ground zero at one extreme, to other situations where the fallout material is spread in a long thin finger. In general, the pattern may be expected to approximate an ellipse. It is clear that such variables as wind conditions and the yields of nuclear bombs and their positions of detonations above different types of surface make it impossible to predict fallout patterns precisely. In the case of nuclear weapons testing these variables are either known or can be predicted with good accuracy. However, in civil defense planning, certain assumptions concerning these variables must be used in estimating not only a single fallout pattern, but also possible overlapping patterns in the event of multiple detonations. RADIATIONS AND FALLOUT ~ In describing and evaluating the effects of fallout patterns, it is necessary to consider the characteristics of the radiations emitted from the radioactive material. These are of three types: rays, beta particles and alpha particles. gamma Gamma rays are the emissions os ,