A characteristic constant for a radionuclide, which is defined in terms of an ideal point source, as [math] \Gamma _\delta =[/math] [math]\frac{\iota^2\ \dot{K}_\delta}{A} [/math] , where [math] \dot{K}_\delta[/math]is the air-kerma rate due to photons (gamma and x rays) of energy greater than δ at a distance [math]\iota[/math] in a vacuum from a point source of the radionuclide of activity A. (Adapted from ICRP Publication 107)
ICRP Glossary entry - 22 February 2019
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