and *°*T exposure rates were obtained by interpolating from the data in Table 2 for the source energies in Table l, multiplying by the number of y-rays emitted per 23°y and Th disintegration and summing. 232 s * . . Calculations of the exposure rates for uniformly distributed sources in the soil are discussed and evaluated together with the differential energy spectra, exposure rate spectra, A. integral and angular exposure rates. Exposure Rates The total exposure rates as well as the direct beam or unscattered component are given in Table 2 as functions of source energy for various detector heights. Figure l illustrates the variation of exposure rates with height for three different source energies. Note that the total expoSure rate changes very little in the first 10 meters above the interface but then begins to drop off fairly rapidly with height with the lower energy sources falling more rapidly than the higher energy sources due in large part to the more rapid decrease of the unscattered component for low source energies. The scattered components fall off less rapidly than the total exposure rate. Since the calculated expesure rates for *°K. **°u series, and the 7°*tTh series all showed though single height almost exactly the same variation with height even their source spectra varied considerably (Table 3), curve is given in Figure 1 for the variation with of the natural gamma emitters. The variation with height of exposure rate, given in Figure 1, us at a single location by making measurements at h - 1 meter and h the natural emitter was crudely verified by ionization chamber = 7 meters above a predominantly (95%) natural y-radiation field. The measured variation in exposure rate with height of 14% compares reasonably well with the 11% reduction predicted by Figure 1, and is within the experimental error. i te oe a