plat me eanattns DD me bd? B. we we Be Exposure Rate Dependence on Air Density The air density used in our calculations was 1.204 mg/cm corresponding to a temperature of 20°C. Since y-ray distances must be measured in mean free paths, the fluxes and exposures for other air densities can be obtained through adjustments to our data as in the case of differing soil densities. Thus, our data at h meters represents the flux or exposure rate at a distance is the new air density. Cc. (1.204 x 10°°/p’)h where po’ Exposure Rate Dependence on Soil Composition and Moisture Content In our calculations, the assumed soil constituent concentrations given in percentage of total weight were Si0g - 67.5%, Alg 03 - 13.5%, Fez03 - 4.5%, COz - 4.5%, and H2 0 - 10. 0%. Changing the composition of the soil medium affects the fluxes and exposures more fundamentally than changes in density since Compton scattering, which is the dominant process at the higher energies, is proportional to the average Z2/A of the soil while photoelectric absorption, which dominates at low energies, depends on the atomic number 2%. Thus, a soil with more water in it would have an increased Z/A due to the lesser number of electrons per hydrogen atom as compared to most of the other soil constituents and, therefore, relatively more Compton scattering. High Z materials in the soil such as iron could also affect the exposure rates and spectra. We investigated this possible dependence on soil composition by comparing calculations for our standard mock soil which has an average (Z/A) of .503 with similar calculations for pure aluminum having a (Z/A) of .482, a range of (Z/A) typical of most soils. Relatively minor differences were found in the exposure rates calculated for these two materials indicating that the radiation field is not extremely sensitive to the exact composition of the soil. For a .662 MeV plane source