Basic theory for the diffusive sampling of radon

From the closed-form solution of the Fickian equation describing the uptake of radon by a diffusive sampler, the following are calculated: 1) the optimal estimate of the time-weighted average radon concentration; 2) the effect of the geometry of the diffusive sampler on performance; 3) the maximum sampling time consistent with a predetermined maximum error in the estimated time-weighted average concentration of radon; and 4) the effects of temperature and pressure on the performance of the sampler. It is shown that the maximum sampling error can be greatly reduced by dividing the adsorbent bed into two layers placed in series and by using a weighted average of the uptakes on the two layers.