Volume traps--a new retrospective radon monitor

A new method to trace back average radon concentrations in dwellings over several decades in time has been developed. This retrospective radon monitor is based on the measurement of the alpha activity of 210Po deposited in volume traps, e.g., spongy materials used for mattresses and cushions. Polyester samples with different densities have been exposed to radon-laden air. The exposures correspond to characteristic radon concentrations between 390 Bq m-3 and 3.9 kBq m-3 over a 20 y period. The precision in converting the 210Po-signal to the radon exposure has been improved by more than one order of magnitude compared to other common techniques. It is shown that this very sensitive method may be applied to almost all types of volume traps used in households.