Evolution and trends of radiation protection

The purpose of this paper is to review the evolution of some important concepts of radiation protection, discussing the change of emphasis or even meaning involved in their use. By following the past trend of such changes, it is possible sometimes to predict the likely evolution of these concepts in the near future. Mainly examined are the concepts of limits and the extension of their use to situations not covered in the past, of optimization of protection and of protection by intervention when the source is not under control. The dose limits are at present only one component of the basic radiation protection recommendations. However, they are usually judged to have great importance, and the fact that the ICRP recommended values have been widely accepted has resulted in a global uniformity that is very positive for radiation protection. The system of dose limitation recommended by the ICRP deals with ''normal'' situations where radiation exposures do occur. The system as such gives no guidance on design criteria for features reducing the probability of disruptive events leading to radiation exposures. However, the underlying philosophy of the system could be used for such purpose. Unnecessary exposures should be avoided and exposures should be kept as low as practicable. These requirements arise from the stipulated existence of risk below the dose limits. (Nogami, K.)