A simple approach to measure the radon equilibrium factor F from air filter gross beta counting.

The internal alpha dose assessment (ICRP 65, 1994) depends on the value of the equilibrium factor F. This parameter is generally not measured and a mean conventional value ranging between 0.4 and 0.6 is assumed, possibly leading to a significant bias in the dose assessments. In this paper, a method for the measurement of F is reported, based on the total aerosol sampling on filters and immediate gross beta counting of 214Pb and 214Bi activities. Measurements are interpreted according to a Raabe-Wrenn and Jacobi simplified room model, leading to an estimate of the individual airborne activities of short-lived radon daughters, the removal parameter and the equilibrium factor. The method was laboratory tested and validated and it is being qualified by field surveys in different indoor environmental conditions.