Figure 1.2

Sources of radon and related radiation exposure pathways.

^*Gamma exposure from radon collected during some mitigation procedures (see Appendix E).

The first four descendants of radon—²¹⁸Po, ²¹⁴Pb, ²¹⁴Bi, and ²¹⁴Po—are also radioactive and are collectively referred to as radon decay products. They are all metals and have half-lives ranging from a fraction of a second to 27 min (see figure 1.1). Indoors, some of these decay products come into contact with surfaces and are removed from the air by a process called plate-out. The rest of the decay products remain suspended in air as free atoms (unattached) or combined with other aerosols (attached). Although it is possible to measure the concentration of each radon decay product suspended in air, they are generally grouped. In addition, the concentration is not presented in terms of activity per unit volume (becquerel per cubic meter), but rather in terms of the total energy that would be released by alpha particles when all the short-lived atoms decayed completely. This quantity is called potential alpha energy (PAE), and the concentration in air