What are the protection principles upon which radiation protection is founded?
As previously noted, the human activities, such as those ranging from nuclear power production to radiation medicine, that add radiation exposure to that which people normally receive due to background radiation, or increase the likelihood of adding exposure are termed practices. The human activities that seek to reduce the existing radiation exposure, or the likelihood of incurring exposure which are not part of controlled practices (e.g., radon in homes) are termed interventions.
For routine conditions involving practices, most exposure of workers and members of the public is the result of normal operating conditions. However, there may sometimes be variations in operating conditions that cannot be regarded as normal. The term potential exposure is used to describe exposure that is not certain to occur, (i.e., an exposure caused by some departure from normality). Potential exposure reflects the combination of the probability of occurrence of potential events, the chance that such events will result in a radiation dose to individuals and the probability of radiation effects from the expected resulting dose.
Bearing these distinctions in mind, radiation protection for practices is founded on a conceptual framework proposed by the International Commission on Radiation Protection (ICRP) and involves three principles: justification, optimisation and limitation.
Justification . No practice involving exposures to radiation should be adopted unless it produces sufficient benefit to the exposed individuals or to society to offset the detriment it causes. In the case of justification, detriment is not necessarily confined to radiation, but may include other social and economic considerations as well.
Optimisation . Once a practice has been justified and adopted, it is necessary to consider how best to use resources in reducing the radiation risk to individuals and the population. For any particular source, the broad aim should be that the magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposure which is not certain (potential exposure) should all be kept as low as reasonably achievable, economic and social factors being taken into account. Because of the interaction of the various factors to be considered, methods for dealing with optimisation are diverse. They range from simple common sense to complex techniques such as cost-benefit analysis.
Limitation . Exposure of individuals resulting from a combination of all relevant practices should be subject to dose limits, or to some control of risk in the case of potential exposure. These are aimed at ensuring that no individual is subject to radiation risks deemed to be unacceptable. Limits provide a clearly defined boundary of individual risk for application of the more subjective procedures of justification and optimisation.
Intervention involves the application of radiation protection principles retrospectively, i.e., when it is decided to reduce existing exposure caused by an accident, contamination from past practices or high natural background which is amenable to being reduced. Two principles are involved in the case of intervention: justification and optimisation.
Justification . The proposed intervention should do more good than harm, i.e., the reduction in radiation dose should be sufficient to justify the social and economic costs involved. However, there will be some level of projected dose for which intervention will almost always be justified because of the acute radiation injury it will produce.
Optimisation . The form, scale and duration of the intervention should be optimised so that the benefits of the dose reduction less its costs are maximised.
The breadth of the conceptual framework for radiation protection has grown constantly throughout the years, from the extremely simple guidance on protection against X-rays issued in the 1930s up to the very comprehensive system of protection which now covers practically all existing sources of human exposure, artificial as well as natural, recommended by the ICRP in its Publication 60. Figure 3 depicts this coverage.