a Sn Those are just tremendous orders of magnitude between those two. However, since the problem is with us, we consider a fallout in a rather ideale ized sort of model, an infinite plane, a smooth Plane -~- no hille, a structure initially with zero attenuation. There are three principal come ponente to the occupant of a structure. There is the component from the roof, there is the scattered contribution from the ground end there is the direot radiation from the ground in this fashion, (indiceting mbleckboard.) . It is both theroretically and ex- nerimentally fensible to determine the direct radiation from the fallout. It can be cale culated quite precisely; that is the vrimary radietion, The scatter situation om the other hend is altogether a different kind of problem, To determine this by oalculation is a rather formidable task, There are unoertainties in the orogss section; the mathematical techniques become involved especially when you go out over many sean free paths, co in order to get some fundamental scattering data we went to the rn [a 1s

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