- FE le Aan me Em Bate tes" Samet sensitive to both source energy and detector height and becomes a very significant portion of the total exposure rate at low source energies and higher detector positions. B. Differential Energy Spectra The effect of the source depth distribution on the differential energy spectra of the scattered energy flux is shown in Figure 14 for a .662 MeV (**’cs) source. At h = 1 meter the spectrum for the distributed source (a = .33) is softer than that for the plane source while at h = 100 meters there is little difference in the shapes of the two spectra. Thus, it would not be possible to make inferences about the depth distribution or the exact exposure rate at ground level by using an altitude measurement of the energy spectra. Cc. Integral Exposure Spectra The softening of the scattered energy flux spectra at h = 1 meter results in a corresponding softening in the integral exposure rate spectra (Figures 15, 16, 17) especially for h = 1 meter. All three figures show the same general features. The diminished influence of the source depth distribution at h = 100 meters is evident. The fraction of the exposure rate due to y-rays below a given energy, E, increases and the total scattered component increases as the source energy decreases, comparable to the result we obtained for the uniformly distributed sources. Again, we must emphasize the need to properly interpret energy dependent dosimeter readings, since at h = 100 meters over 20% of the exposure rate from an *87>T source (.364 MeV) is due to y-rays of energy less than 100 keV as opposed to a corresponding 6% for 1.25 Mev D. (°° co) y~-Yays. Angular Distributions For a plane source or even a source distributed slightly with depth, at detector heights close to the interface the Ay We