How long does it take for radon and radon decay products to reach secular equilibrium?

The concept of secular equilibrium in the context of radon and its decay products refers to the situation where the rate of production of radon decay products equals the rate at which they decay, leading to a consistent concentration of these products over time. For radon, this process typically takes about 4 hours.

This duration is primarily due to the half-lives of the various radon decay products, notably radon-222 and its immediate decay products like polonium-218 and lead-214. The effective half-life of these products results in the establishment of equilibrium within approximately 4 hours after radon is introduced into an environment. Thus, after about this time frame, the concentration of radon decay products becomes stable and reflective of the existing radon levels.

Understanding this equilibrium is crucial for accurate radon measurement and assessment, as it helps technicians determine when to take measurements for reliable data.