What measurement is derived from the gamma decay of which isotopes in ACD testing?

The correct measurement in ACD (Alpha Continuous Detection) testing derives specifically from the gamma decay of Pb-214 and Bi-214 isotopes. These isotopes are part of the decay chain of Radon-222 (Rn-222), which is a naturally occurring radioactive gas and a significant health concern due to its potential link to lung cancer.

In the decay chain, Rn-222 decays into Pb-214, which subsequently decays into Bi-214. Both of these isotopes emit gamma radiation as they decay, and this emitted gamma radiation can be measured to assess the presence and concentration of radon and its decay products within the tested environment. Therefore, their detection is essential in radon measurement and evaluation protocols, particularly as they indicate radon exposure levels in a given location.

Through the monitoring of gamma emissions from these isotopes, practitioners can gauge the extent of airborne radon and the associated risks, making it crucial for radon mitigation efforts.