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Energy dependence due to changing
Stopping-power ratios
6 MV photon beam
n=narrow beam (
=0.5 cm)
b=broad beam (
=10 cm)
Heydarian
et al
Cylindrical air ion chambers can
be used without correction for
energy variations in high
energy photon beams, incl. Co-
60 (IAEA TRS-398).
The secondary electron energy
spectrum is not changing with
depth.
Ratio narrow/large field depth dependence
Difference <0.5%