Gamma radiation from radon daughters in the atmosphere

The gamma ray flux and ionization from the decay products of 222Rn in the atmosphere and the corresponding photon energy and angular distributions as a function of height above the air-ground interface have been calculated for several vertical 214Pb and 214Bi concentration profiles. These physical properties are compared with the corresponding radiation field resulting from sources in the soil. It was found that for normal turbulence the radon daughter gamma flux at ground level is only about 2% of the typical soil source flux, whereas for an inversion this ratio is of the order of 20%. At 100 m, radon daughters account for about 5% of the total gamma flux for normal turbulence and about 25% under inversion conditions. At 100 m the radon daughter produced flux is harder than the flux from soil sources, and the skyshine of gammas greater than 500 keV is much larger than the skyshine from soil sources. These results suggest means of separating out airborne radon contributions from total gamma flux or ionization measurements. Other applications of the calculated results to natural background radiation variations, natural fallout, and measurement interpretation are discussed.