Physics Athens 2016

Photons are indirectly ionizing

Photons deposit energy in the medium through a two step process: 1. energy is transferred to charged particles released in the medium 2. the released charged particles act as directly ionizing radiation

KERMA : K inetic E nergy R eleased per unit Ma ss (J/kg = Gy) Sum of initial kinetic energies transferred from indirectly ionizing radiation to charged particles (electrons) in a sample of matter

• initial kinetic energies of e - 1 contribute to the KERMA as both were generated in V, e - 3 was generated outside V, so does not contribute and e - 2

e -

1

e -



2

• e -

and e -

3 contribute to the Dose in V, while e - 2

1

deposits energy outside V, so does not contribute

V

e -

3