Implications of Optimization in the Draft ICRP Recommendations

Dose constraints, dose limits and optimization are the very important frame in the radiological protection. It should be better to clear the definition of these important items for the future radiological protection. LNT was the basic concept for establishing the radiological protection system including these items. ICRP said in the draft of new recommendations that the concept of linearity was changed. The linearity as the essential change has the meaning in the region of above a few mSv/year. The existence of natural background radiation provides a benchmark for judgment about their relative importance of additional exposures. The effective dose from natural background varies by at least a factor of ten around the world. If the highest radon doses are included, the concern should begin to be raised at the higher end of the natural range. In this context a few mSv is the band that natural background varies in a year. This means that a few mSv/year as the additional dose is ignored in the concept of LNT. Even if some sources are assumed, 1mSv as the constraint is justifiable. Optimization should be performed to the additional dose beyond 1mSv, and ALARA is a process regarding this optimization. A rational radiological protection system can be built by clarifying the object and the target range with regard to LNT and optimization (ALARA). And the total radiological protection system including NORM will be established by clarifying constraints that are based on the natural background. (Author)