Passive, integrated measurement of radon using 5A synthetic zeolite and blue silica gel.

Synthetic zeolite of 0.5nm pore size (5A) and blue silica gel were tested to determine their capability to be used as radon collectors. Tests conducted in a radon chamber under controlled conditions of temperature and relative humidity indicate that simple, inexpensive and maintenance-free passive devices containing about 250g of synthetic zeolite or about 270g of blue silica gel in open face metal canisters that can measure radon conveniently and adequately, the latter though being suitable only for dry-medium dry atmosphere with quite high radon concentrations. Both materials can be recycled for reuse, in a way similar to the recycle and reuse of active carbon. The amount of radon adsorbed in such collectors is determined by counting the gamma rays from the radon decay products. The lower limit of detection (LLD) is estimated to approximately 45Bqm(-3) for the synthetic zeolite and to approximately 350Bqm(-3) for the blue silica gel, for an exposure of 48h at a relative humidity of about 50%. In comparison, the corresponding LLD for active carbon is estimated to 10Bqm(-3). At relative humidity in the range between 10% and 50%, radon chamber experiments indicate that the measured radon in the canisters is proportional to the mean concentration of radon during the period of exposure. It is estimated that calibration uncertainty lies within +/-20% for both materials, thus suggesting that at least detectors based on the 5A synthetic zeolite presenting a reasonably low LLD, are a feasible and of similar cost alternative to activated carbon for indoors radon concentration measurements in practical situations.