Environmental radiation monitoring in the context of regulations on dose limits to the public

Many countries have regulations that limit the radiation dose to members of the general public. Most are consistent with the ICRP and are moving towards a 1 mSv annual dose limit, with some specifying additional lower limits to allow for exposure from multiple sources. Such limits currently being considered are in the range of 0.10 mSv to 0.30 mSv. Limits apply to all pathways, and, therefore, will require dose modeling. Measurements of the external dose could help to verify the assumptions made in dose modeling codes. Based on long-term measurements of the natural background radiation, assessing an additional external dose on the order of 0.15 mSv or more would be possible using currently available technology. However, interpretations of any environmental monitoring data require knowledge of the natural background radiation field and its variations. Results from international intercomparisons demonstrate that passive dosimeters, such as TLDs, are appropriate devices for measuring the external dose off-site. National standards being developed for such devices should address the needs of regulations on dose limits. Active instruments such as PICs and GM detectors are useful for real-time monitoring or spot measurements, and provide more information than may be needed to demonstrate compliance with public dose limits. Limits of 0.15 mSv or less may require more extensive measurements with spectrometers and calculations of derived limits for soil concentrations, similar to those being presently developed in the U.S. for decommissioned sites. (author)