Environmental radiation dosimetry with ionization chambers and thermoluminescence dosimeters

Inferring dose to man from measurements of externally incident radiation implicitly involves relating the responses of radiation detectors to those of another set of 'detectors', the organs of interest. For environmental radiation fields, the energy and angular distributions of the flux densities of the significant components under representative or specified conditions have been reasonably well established. The responses of detectors can then be calculated as a function of the total flux densities in the detector-free air, or of proportional quantities such as ionization rate or absorbed dose rate. These data yield the desired calibration of detector response in terms of organ dose, usually to an accuracy of about +-10% (s.d.). This approach was employed to environmental radiation dose assessment in the interpretation of the responses of ionization chambers and thermoluminescence dosimeters to environmental photons and cosmic-ray charged particles. These responses were shown to be proportional to mean absorbed dose rates in the detector media in both photon and muon fields. Published data on particle spectra in environmental radiation fields are then applied to the calculation of detector response in such fields. A consistency check is available from the close agreement (+-5%) between the values of absorbed dose rate in free air inferred from the responses of the two detectors in a variety of such fields. This methodology is contrasted with that recommended in ICRU Report 19 for radiation protection purposes, where a difficult determination of the maximum absorbed dose in a 30 cm diameter sphere of soft tissue is presumed to appropriately characterize ambient radiation fields