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Air Kerma-rate constant Γ
δ
A
K r
δ
δ
&
⋅
=Γ
2
tr
E
1
Γ
δ
μ
⋅ ⋅
=
For the case of a point source with a known photon spectrum the above
expression takes the following form:
E,
4
α
ρ
π
∑
⋅ ⋅
⋅
=
E,
tr
i
i
En
4
1
Γ
α
δ
ρ
μ
π
where n
i
is the number of photons emitted with energy E
i
per disintegration and (µ
tr
/ρ)
α,Ei
is the mass energy transfer coefficient of air for the photon energy E
i
.
i is the index over all emitted photon energies E
i
with E
i
>
δ
.
i
i
ρ