The probability of PE – rule of 3s:

  • Incidence Electron must have enough energy to overcome the binding energy:
    • Classic Example: 33.0 keV photon will NOT be able to lose the 33.2 keV K shell electron iodine.  (it might knock loose the L or M – but not the K).
  • PE is MOST likely to occur near the binding energy (assuming its greater)
    • Classic Example: 34.0 keV photon is more likely to knock loose the 33.2 keV K shell electron from iodine, relative to a 100 keV phonon.
    • In FACT! This is described in a highly tested way:
      • PE Probability ~ 1 / Energy Cubed Or  1/KvP^3
  • The tighter the electron is bound the more likely the PE
    • Tighter bound electrons live in higher Z atoms
    • The K shell is actually favored in lower Z atoms because it is most tightly bound
    • Classic Testable Math:
      • PE Probability ~ Atomic Number Cubed