Natural Radionuclides in the Atmosphere

Abstract

Natural radioactive nuclides in the atmosphere have two principal sources—radon and its progeny derived from Earth’s surface and cosmic-ray-produced nuclides. Dust from the elevation of soils can also provide secondary sources of these nuclides. Suitable accommodation for these sources must be made if only those species having gaseous precursors are to be considered. There is a radon isotope in each of the three major natural-decay chains: 238U (222Rn, half-life ¼ 3.8 d), 232Th (220Rn, half-life ¼ 55 s), and 235U (219Rn, half-life ¼ 3.9 s). Almost all radon in the atmosphere is produced in soils and is transported to the atmosphere by diffusion. Because its longer half-life allows for greater diffusive transport, most radon entering the atmosphere is 222Rn; its radioactive decay scheme is presented in Table 1. An early summary of 222Rn and its progeny in the atmosphere was provided by Turekian et al. (1977). Table 2 lists the radioactive species produced by cosmic rays acting on the gaseous components of the atmosphere, which include nitrogen, oxygen, and all the rare gases as targets. A detailed discussion of the formation of radioactive species by cosmic-ray bombardment has been published by Lal (2001) based on his pioneering work since 1967 in a classic paper by Lal and Peters (1967). Radiocarbon (14C) is not discussed in this chapter. Because of its central role in many Earth’s surface processes, a separate chapter is found in this volume (see Chapter 4.09). (Table Presented). There are more than 30 radionuclides produced in the.