+t fue te ate © oe cain cote Ted te fle understand the significance of these variations to properly interpret as well as predict the results of fallout measure- ments made either at ground level or from an airplane or helicopter. Thus, the results of our computations of radiation due to exponentially distributed sources are discussed in this light. A. Exposure Rates Total exposure rates for exponentially distributed sources of source strength one gamma emitted per cm® of interface surface are listed in Table 5, A. Unscattered exposure rates are tabulated separately in Table 5, B. The data in Table 5 should be sufficient to allow the reader to construct exposure rate vs. height curves for any source energy and relaxation length. The dependence of the exposure rate on detector height is shown in Figures 8, 9, and 10 for several source energies and depth distributions. (a ~ © corresponds to a plane source. All our calculations of the scattered component for a plane source were arrived at using a = 10,000. lated exactly.) The unscattered component was calcu- From Figures 8 and 9 we see that the variation with detector height is relatively insensitive to source energy, especially below h = 100 meters. Figure 10 illustrates the effect of the depth distribution on the exposure rate at various detector heights. The scattered component falls off very slowly with height all the way up to about h = 30 meters, but as the depth distribution approaches a plane source the unscattered component causes the total exposure rate to begin to drop off more quickly with height. The exposure rates for various depth distributions all tend to converge at higher altitudes, i.e. the effect of the source depth distribution is reduced. This is qualitatively what we would expect when using an exponential source distribution model to represent ground roughness, since ground roughness effects decrease as the detector height is increased.