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Air Kerma-rate constant Γ
δ
A
K r
δ
δ
&
⋅
=Γ
2
Ideal point source S of a specific radionuclide positioned at a given position in free
space with activity A
Air-filled volume element dV at the point P in a radial distance r from the point
source
The source is emitting
a single photon of energy E per disintegration
(E >
δ
)
EA
r 4
1
EA
da
1
r 4
da
Ψ
2
2
⋅ ⋅
⋅
= ⋅ ⋅
⋅
⋅
=
π
π
&
The energy fluence rate of photons at P is given by:
isotropic emission