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Reference Air Kerma Rate K
R
= K
α,α
(r=1m)
in
m
Gy . h
-1
at 1 m
r = 1m
air
Reference Air Kerma Rate
/ Source Strength
r
The reference air kerma rate of a source is defined as the air kerma rate in air at a
reference distance of one metre from the centre of the source,
corrected for
attenuation and scattering in air. This is the air kerma rate
in vacuo
. For rigid sources
usually considered in the practice of brachytherapy (as distinct from malleable wire
sources), the direction from the source centre to the reference point at one metre has
to be at right angles to the long axis of the source.
In 1985, the ICRU Report 38
5
defined as an emission specification quantity for γ-rays emitting brachytherapy sources
the
reference air kerma rate
.
)m1 r(K