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When the volume element dV in the radiation field is filled by air then we have the
air kerma, K
α
.
Exposure X and Air Kerma K
α
Then the following relationship between exposure X and air kerma K
α
exists
e is the elementary charge and W is the mean energy expended in air per ion pair
)g1.(K.
W
e
X
a
a
−
=
dm=ρ
α
.dV
air
e
-
dm
dQ
X
=
dm
dE
K
tr
=
formed, W/e = 33.97 J.C
-1
.
a
g
Is the mean value of g
α
, the fraction of the energy of the electrons liberated by
photons in air that lost to radiative processes (bremsstrahlung and fluorescence,
g
α
< 0.3% for E
≤
1MeV).