III. RADIATION IN AIR DUE TO THE UNIFORMLY DISTRIBUTED NATURALLY OCCURRING SOURCES IN THE SOIL Gamma radiation in air due to naturally occurring isotopes in the soil is usually calculated by assuming uniform distribution in the soil. The only natural emitters of consequence are *°x, 23°y, and *°*Th. The latter two isotopes decay by means of a long chain process and *°x decays to *°~n with the emission of a Single 1.46 MeV y-ray. For the 7°°U series, most of the yY-rays are emitted by Rac (77* Bi) and RaB(***Pb) which are daughters of 222Rn, a gaseous daughter of #®6Ra. Because it is a gas, 222Rn can emanate from soil particles, diffuse through the soil air to the surface and escape into the atmosphere. This effect tends to reduce the y-ray emission in the soil due to 238 U 2381 by as much as 50%, thus lessening the importance of the series relative to the other two emitters‘*?. ‘The 797th series contributes a large number of y-rays of varying energies from several different daughter isotopes. Although one of these emitters is a gas, thoron (77°Rn), the short half life of this isotope (54.5 sec) prevents any significant escape and subsequent loss of soil gamma activity. 226 232 Since the decay schemes of Ra and Th (particularly the relative intensities of the various decay levels) are still somewhat uncertain, we give in Table 1 the source spectra and intensities used for the calculations in this report. These energies and intensities are our estimates based on the best available data. Some of the weaker energy lines have been grouped together or included with stronger lines in order to keep the total, number of source energies manageable. Table 2 gives the exposure rates for monoenergetic sources ranging from 0.25 to 2.75 MeV vs. detector height so that if necessary the reader can recalculate 7°*u and 232 0h exposure rates for other source spectra. The #38 y yh 4