for a gamma or X-ray emitting nuclide, the quotient of by A, where (dХ/dt)δ is the exposure rate due to photons of energy greater than δ at a distance l from a point source of this nuclide having an activity A
A special unit of exposure rate constant is Rm2h−1Ci−1.
NOTE – It is assumed that the attenuation in the source and along l is negligible. In the case of radium, the value of Γ is determined for a filter thickness of 0,5 mm platinum. Moreover, Γ is related not to the activity but to the mass of 226Ra; a special unit is then Rm2h−1g−1.
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