Dose Course 2018_Flipping book

Energy dependence of detector response (photon interactions within the detector)

Energy absorption coefficient ( μ en

/ ρ ) ratios, norm. at 1 MeV

100

Max ratio ~115 at 40 keV Z Ag =47

Film (Ag based)

Silicon (Diode)

Air (Ion chamber)

10

Film (Nylon based)

Carbon (Diamond)

Max ratio ~8 at 30 keV Z Si =14

Isooctane (LIC)

Medium / Water

1

Max ratio ~1.1 at 30 keV Z eff (Air)  7.6

0.01

0.10

1.00

10.00

Z

(water)  7.4

eff

Min ratio ~0.33 at 15 keV Z eff (Isooctane)  5.4

0.1

Photon energy (MeV)

What is meant by “Energy dependence”? A varying relation between the detector signal and the investigated dose (water), caused by spectral changes of the beam.