2.3. Interaction of Photons with Matter 83
Photon Energy1 Mb1 kb1 b10 mb
10 eV 1 keV 1 MeV 1 GeV 100 GeV(b) Lead (Z = 82)
− experimental σtot
σp.e.κeCross section (barns / atom)Cross section (barns / atom)10 mb1 b1 kb1 Mb(a) Carbon (Z = 6)σRayleighσRayleighσComptonσComptonκnucκnucκeσp.e.− experimental σtotFigure 2.3.1: Photon cross sec-
tions as a function of energy for
carbon and lead (19).a photon beam as it passes through a material. Before we go into that discussion,
let’s have a closer look at the most important photon interaction mechanisms.
A.1 PhotoelectricEffect
In the previous chapter we introduced the concept of wave-particle duality, according
to which light sometimes behave as particles. Photoelectric effect is one of the
processes that confirm this idea. It was originally explained by Einstein and earned
him a Nobel Prize. The effect is rather simple: when light shines on a material,
electrons can be emitted. The emission of electrons, however, does not depend on
the intensity of light, rather on its frequency. If the frequency is lower than a certain
value, that depends on the target material, no electrons are emitted. Certainly this
can not be explained on the basis of classical wave-like picture of light. Einstein