ICRU Report 95

Operational Quantities for External Radiation Exposure

Prepared jointly with ICRP
Abstract - Operational, measurable, quantities for external radiation protection complement the protection quantities, which are, by their nature, not measurable. Operational quantities are used for prospective and retrospective assessments of radiation fields, by measurement or calculation. Personal dosimeters and instruments for area monitoring are designed to indicate the operational quantities and are routinely calibrated with standard radiation fields that can be related to the operational quantities.
The definitions of the operational quantities for personal and ambient dose equivalent in International Commission on Radiation Units and Measurements (ICRU) Report 39 (1985), Report 43 (1988), and Report 51 (1993) give acceptable estimates of the International Commission on Radiological Protection (ICRP) protection quantity effective dose (2007) for photons in the energy range from 70 keV to 3 MeV. At lower and higher photon energies, the ICRU Report 39/51 defined operational quantities show significant over- and underestimates of the protection quantities, respectively. Furthermore, the conversion coefficients given for the operational quantities have been calculated only for a limited subset of particles: photons, electrons, and neutrons.
This Report recommends alternative definitions of the operational quantities that are better estimators of the protection quantities than those previously given. Conversion coefficients from physical field quantitiesfluence and, for photons, air kermaare given for the following particle types over wide energy ranges: photons, electrons, neutrons, protons, muons, pions, and helium ions. This Report recommends that instrument manufacturers and developers work to develop revised dosimeters and instruments that accurately provide measurements that conform to these recommendations. This Report also recommends that international and national authorities recognize the need for a gradual and prudent period of adoption to balance the costs of implementation with the benefit of a more coherent system of operational quantities, representing the protection quantity in measurement.