Weighting factors for radiation quality: how to unite the two current concepts

The quality factor, Q(L), used to be the universal weighting factor to account for radiation quality, until—in its 1991 Recommendations—the ICRP established a dichotomy between ‘computable’ and ‘measurable’ quantities. The new concept of the radiation weighting factor, wR, was introduced for use with the ‘computable’ quantities, such as the effective dose, E. At the same time, the application of Q(L) was restricted to ‘measurable’ quantities, such as the operational quantities ambient dose equivalent or personal dose equivalent. The result has been a dual system of incoherent dosimetric quantities. The most conspicuous inconsistency resulted for neutrons, for which the new concept of wR had been primarily designed. While its definition requires an accounting for the gamma rays produced by neutron capture in the human body, this effect is not adequately reflected in the numerical values of wR, which are now suitable for mice, but are—at energies of the incident neutrons below 1 MeV—conspicuously too large for man. A recent Report 92 to ICRP has developed a proposal to correct the current imbalance and to define a linkage between the concepts Q(L) and wR. The proposal is here considered within a broader assessment of the rationale that led to the current dual system of dosimetric quantities.