ABSTRACT
The dosimetric quantities exposure and absorbed dose have been in use since the 1920s and 1950s, respectively. In the 1970s, special dosimetric quantities were defined (ambient dose equivalent and personal dose equivalent) for area monitoring and personal monitoring, respectively, and the methodology for realizing these quantities was developed by the International Commission of Radiological Protection (ICRP) and the International Commission on Radiation Units and Measurements (ICRU). This chapter gives a brief introduction to these developments. The use of physical dosimetric quantities preceded radiation protection quantities, and they are still the fundamental quantities and standards on which all radiation protection quantities and measurements are based. Free-air ionization chambers (FAIC) and graphite cavity ionization chambers are being maintained as primary standards of exposure or air kerma in the primary standards dosimetry laboratories (PSDLs), in the respective photon energy ranges. FAIC is the primary standard of exposure or air kerma for kV X-ray beams.
