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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
.
Then the following relationship between exposure X and air kerma K
α
exists
Exposure X and Air Kerma K
α
e is the elementary charge and W is the mean energy expended in air per ion pair
formed, W/e = 33.97 J.C
-1
.
)g1.(K.
W
e
X
a
a
a
g
dm=ρ
α
.dV
air
e
-
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).
dm
dQ
X
dm
dE
K
tr