Photoelectric Cross Section

This cross section is called the thomson cross section symbolized by the greek letter sigma with subscript zero σ 0 and is equal to a numerical factor times the square of the term electric charge squared divided by electron rest energy or σ 0 8π 3 e2 mc2 2.

Photoelectric cross section. The dependence of the photoabsorption cross section on the energy of gamma quanta has the form of a decreasing stepped curve. Each step is associated with the contribution of one of the inner shells of the atom. Photoelectric cross section over broad range at high e cross section goes as 1 hν.

In a crude approximation for photon energies above the highest atomic binding energy the cross section is given by. The probability of the photoelectric effect occurring is measured by the cross section of the interaction σ. Cross section in most cases.

At lower e σ goes as 1 hν 3 5 the dependence on z varies somewhat with energy too that s why z 5 or z 4. Hence particularly for medium and high z elemen ts a plot of pe v ersus the photon energy exhibits the c haracteristic sa wto oth absorption edges since the binding energy of eac h electron subshell is attained. Note on nist x ray attenuation databases.

Ho w ev er if the photon energy drops b elo w the binding energy of a giv en shell an electron from that shell cannot b e ejected.