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Dose calculation – AAPM-TG43: The Source Strength
That is, the air kerma strength, S
K
, defined as the product of the air kerma rate
in free space at a measurement distance r from the source center along the
perpendicular bisector, K
a
(r), and the square of the distance r.
This is the actual strength of the specific source we consider.
r
2
K
r)r(K S
The recommended unit for air kerma strength
S
K
is µGy.m².h
-1
and has been denoted by the
symbol U:
1U = 1 µGy.m².h
-1
= 1
cGy.cm².h
-1