Introduction to Radon & Health Risk
The Fundamentals of Radon & Radioactivity
Radon Occurrence & Behavior
Radon Measurement & Devices
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Radon Half Life Progression

When a radium atom decays, radon gas is released into the surrounding air or water. Since radon-222 has a half-life of 3.8 days, it has enough time to move from its radium source into buildings, where both the radon and its decay products can be inhaled, delivering a dose of radiation to the lung tissue.  The decay products of radon 222 – polonium-218, lead-214, bismuth-214, and polonium-214 – have very short half-lives. These decay products account for the major portion of the dose of radiation received in most situations and are the primary source of radon-induced lung cancer.  Notably, polonium-218 and Polonium-214 are the alpha emitters that do most of the damage to the lung tissue and DNA. Bismuth-214 and lead-214 are beta emitters and also produce most of the gamma radiation in the decay series.

Figure 2-8
Uranium Decay Chain Progression Chart
Source: A.P. Jacobson