ICRU Report 88, Measurement and Reporting of Radon Exposures


Lung cancer risk caused by the inhalation of radon (222Rn) and its short-lived progeny is related to lung dose, which cannot be directly measured. The only measurable parameters which allow the determining of lung doses are the radon and radon progeny activity concentrations and related size distributions. Although lung cancers are caused by the inhaled short-lived radon progeny and not by the radon gas, it is the radon gas which is commonly measured and not its progeny. Since radon gas measurements are much easier to carry out, require less expensive equipment and are especially suited for long-term measurements, the report focuses on the measurement of the radon gas for specific exposure conditions in homes and workplaces. The first objective of this Report is to provide information on how to measure radon, covering measurement techniques of radon in air and water, currently available detection systems, and measurement strategies most appropriate for the desired goal of a measurement campaign. Critical measurement strategy decisions are the selection of the measured radionuclide (i.e., radon gas or radon progeny and related size distributions), choice of the measurement period (i.e., short-term or long-term measurements), the choice of detector and its deployment, the type of measurement (i.e., areal or personal measurements), the survey strategy (i.e., integral or time-resolved measurements), or the strategy to accomplish the specific goal of a survey (i.e., measurements describing the current status or retrospective measurements). The choice of a specific strategy depends on the purpose of the survey, and differs therefore between the demands of a nation-wide indoor radon survey or an epidemiological study.

The second objective of this Report is how to interpret and report the results of these measurements, the associated uncertainties, and the resulting dosimetric estimates. Care should be taken when reporting and interpreting radon measurements because measured radon activity concentrations exhibit significant spatial variations (i.e., local and areal), and temporal variations (i.e., diurnal, seasonal, and annual) variations. Consequently, estimates of the average annual radon activity concentrations are typically used for radon surveys and are compared with reference levels for radiation protection purposes. Other factors that may affect the interpretation of radon measurement results and the related dose estimates include thoron (220Rn) interference on radon detection systems, variations of aerosol parameter, equilibrium factor, duration of exposure (i.e., occupancy times in a building or location) and breathing rates. Often encountered problems are the uncertainties in extrapolating short-term measurements carried out at different locations within a building, or at different times during a year or in different years to statistically reasonable average values.

Finally, the third objective of this Report is to provide recommendations on optimal measurement strategies, measurement techniques, recording and reporting of measurements for different measurement objectives, such as individual exposure, average population exposure in a region or country, epidemiological studies or compliance with reference levels in radiation protection.