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Description
Radon is a colourless, odourless radioactive gas which is the largest source of our annual radiation dose. It can only be measured using detectors, which can be passive or electronic.
Passive radon detectors are cheap and easy to manufacture or to buy, so companies can provide a radon measurement service for householders and employers. The accuracy of the detectors depends on various factors, such as how they have been stored before use, the sensitivity of the plastic detection medium, the design of the detector casing, the method used to etch the detector medium, how the exposed pits are counted, plus staff training, record-keeping and reporting of results.
In view of this, laboratories undergoing accreditation or renewing their accreditation should take part in recognised intercomparison exercises each year, where their detectors and those of other laboratories are exposed to a range of radon levels in a radon chamber. Their reported results are then compared against a reference instrument (e.g. ATMOS 12 DPX ionization chamber calibrated annually against a radon gas source from an accredited radon laboratory) to determine the performance classification. This can be useful for laboratories to confirm that their systems are working properly or to discover where they can make improvements.
UKHSA and its predecessor organisations have been carrying out the intercomparison every year, for over 40 years, typically for around 30 laboratories worldwide. All passive detectors are exposed side by side to 5 different exposures in our radon chamber, plus a transit group that is not exposed, which acts as a transit control. The detectors can be etched track, electret or (for UK laboratories only), charcoal.
Laboratories are ranked according to their performance (accuracy and precision). Anonymised results are shown from a recent intercomparison.
For those interested in taking part in future intercomparisons, or for more information, please contact radon.calibration@ukhsa.gov.uk.