for a radionuclide emitting photons, the quotient of by A, where Kδ is the air kerma-rate due to photons of energy greater than δ, at a distance 1 from a point source of this nuclide having an activity A
NOTE – The SI unit of air kerma-rate constant is m2 • J • kg−1.
When the special names gray (Gy) and becquerel (Bq) are used m2 • J • kg−1 becomes m2 • Gy • Bq−1 • s−1.
When the earlier special units of activity (the curie) and kerma (the rad) are used
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