Fundamental Research Division
From the source to the dosimetric impact assessment
The objective is to estimate as precisely as possible the committed effective dose, i.e. over a lifetime, or the equivalent dose to an organ. Several factors are taken into account and the process differs whether it is a question of irradiation or internal contamination.
Dosimetry consists in measuring (in case of external radiation) or estimating (in case of internal contamination) the committed effective dose, which depends on:
For irradiation, detection systems are calibrated and certified to be directly proportional to the dose received. An adjustment must be made to transpose operational quantities into dosimetric quantities depending on the heterogeneity of the irradiation, exposure time, rate and the nature of the emission.
As the level of internal contamination is not directly measurable, estimating the dosimetric impact is more complex. Indeed, evaluating the amount incorporated and then calculating the dosimetric detriment requires having an appropriate biokinetic model for the radionuclide(s) involved. These models and data are provided by the International Commission on Radiological Protection (ICRP). In practice, however, the use of these models is based on forming hypotheses regarding the circumstances of an incorporation event (either known or suspected), such as the chemical and physical characteristics of the radioactive contaminant to which the individual has been exposed, and the time interval between incorporation and the measurement. Repeated measurements over time make it possible to clarify the hypotheses and to refine the model, for a better dose evaluation.
To help address the health risks, the dose must be expressed in terms of the committed effective dose (50 years for workers) for all external and internal components, or as an equivalent dose to the most irradiated organ, or as an absorbed dose.
Indeed, the ICRP has defined radiological protection quantities, to determine the dose limits for occupational exposure. This ensures that deterministic effects can be avoided, and that the risk of developing stochastic health effects can be maintained at an acceptable level.
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