The Present System of Quantities and Units for Radiation Protection

The International Commission on Radiation Units and Measurements has over the last decade developed operational quantities, the ambient, directional and personal dose equivalent, suitable for the measurement of radiation fields in a variety of circumstances. Experience with the use of these quantities to represent the dose limitation quantities defined by the International Commission on Radiological Protection in 1977 has been an important part of recent radiation protection metrology. The definition by International Commission on Radiological Protection in 1991 of new limitation quantities, the equivalent dose and the effective dose has necessitated a redirection of this work. The metrology field has made good progress, however. It has found that for photons, at least above 50 keV, the effective dose can be measured by the ambient dose equivalent about as well as the former effective dose equivalent. Unfortunately, for neutrons the existing and already quite severe complications have been made somewhat worse by the new quantities although not any worse in the important region between 0.1 and 1 MeV. Neutron measurements over a broad energy range are the subject of extensive evaluation and some new suggestions as the metrology field wrestles with these problems. Values of wR constitute an important part of the International Commission on Radiological Protection recommendations. A brief history of the development of higher relative biological effectiveness values for fission neutrons and alpha particles leading to the selection of 20 for wR in each case, is provided.