Active radon detectors require a power source and are generally much more expensive than a passive detector. However, they can usually be used for considerably more tests than an individual passive detector.

There are two classes of active radon detector. One measures radon gas concentrations and the other measures the amount of radon ‘daughters’ or decay products, in the air.

Whilst it is the breathing in of radon daughter or ‘decay products’ that is of most concern, it is easier to measure the radon gas concentrations as more factors will affect concentrations of the decay products.

Active devices include those which record a single measurement from a sample of air and instruments which are automated to collect and analyse several samples in succession. These latter instruments can thus show how radon concentrations change over a period of time. This can be useful for specialist diagnostic work and for indicating potential radon problems over a shorter time scale than a passive device might show. The height of a measured ‘peak’ might indicate the strength of the radon source the property can draw on in certain conditions. In the case of a house purchase requiring a result in a few days, the pattern of the radon fluctuations coupled with temperature measurements made with the instrument can indicate whether the test conditions have been maintained and thus add credibility to the test result.

Once a remedial system has been installed it is recommended that follow up testing be carried out. This would normally be a 90 day test using alpha track detectors. Where it is required to determine if the installed measures appear to be working in a shorter time scale we offer a three day before and after test using RAD7 continuous radon monitors. This would consist of a three day test shortly before the work is undertaken followed by a further three day test on completion. Where previous radon levels were high (500 Bq/mł and above) a substantial reduction might be expected if the system was being effective. (This could be confirmed by a further 90 day alpha track measurement.) If however the results remained high it would indicate that the original source or problem had been misdiagnosed and that further investigations were in order. This could result in a saving of several months over the alternative of deploying alpha track devices only and waiting for the result. 3 day test.