Handbook of Radon.
8. Monitoring for radon: methods and discrepancies.
Measurements of radon in buildings over short periods (even over a few days) may give a poor estimate of the annual average level. Readings taken over minutes or hours are largely meaningless except in research work.
Most domestic radon monitoring in the UK has been undertaken using 'plastic' or 'track-etch' detectors that are capable of integrating radon over periods as long as a year. These cost around £20 each, including analysis, and are used typically for three month periods. They are generally accurate to within 20%, but larger systematic differences between different makes have been observed. An explanation of the working principle is given in Section 36.
Notwithstanding that radon daughters deliver most of the dose to lung tissue it is the long-term average radon gas level in a building that may be monitored to determine health risks and for assessing the effectiveness of most types of remedial measures. For most purposes therefore, track-etch detectors are suitable.
However, in the USA extensive use has been made of a different type of device, the charcoal canister. For several reasons, these are not recommended by many scientists, and inappropriate concern or complacency can result from placing reliance on results from these units. Concern might be even greater in the UK, where naturally ventilated houses would be expected to exhibit greater short period fluctuations than are the norm in many American dwellings.
In old heavyweight houses typical of parts of Devon and Cornwall, summertime readings with track-etch detectors may be suspect. During months of hot weather these houses are often cooler indoors than outdoors, a reversal of the conditions that are responsible for much radon entry (see Section 11). It has been discussed for years that summertime measurements are suspect in some types of houses, but they have been continued. These houses may be worse affected than reported results would suggest.
Another type of detector, the electret ion chamber, has demonstrated good test accuracy and performance on site and is rapidly gaining acceptance amongst scientists. However, it is affected by gamma fields and care needs to be exercised in its use.
The proven deficiencies of some track-etch detectors have included end errors (substantial errors of measurement at low radon exposures) and gradient (calibration) errors. These have affected readings over the whole range of integrated concentration. Both types of error are relevant in assessment of national statistics, since the fraction of houses estimated to be above any given 'action level' may be markedly affected. Further information is given in Section 36.
KEY FACTS:
Screening using commercially available track-etch or charcoal detectors is poor value compared with the free and confidential service offered by DOE in the affected areas of the UK (see Section 9).
Short term tests using portable radiation monitors can be misleading in respect of assessing either long term average radon levels or the differences room-to-room. Indeed variations room-to-room can depend on which way the wind has been blowing.
Summertime readings in some types of houses may be particularly suspect.
A well known scientific law applies to radon measurements, especially to those using some track-etch detectors:
if you want to measure something accurately only do it once!
Diagnostics measurements in buildings are discussed in Section 59.