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Photoelectric effect

Two-stage atomic diagram of the photoelectric effect. Stage one: an incident x-ray photon is fully absorbed by a bound inner-shell (K) electron, which is ejected as a photoelectron with kinetic energy equal to the photon energy minus the binding energy, leaving the atom ionised. Stage two: an outer-shell electron drops into the K-shell vacancy, releasing either a characteristic x-ray or an Auger electron. The interaction probability is proportional to Z cubed over E cubed and requires the photon energy to exceed the binding energy.

Photoelectric effect geometry Two-stage atomic diagram of the photoelectric effect. Stage one: an incident x-ray photon is fully absorbed by a bound inner-shell (K) electron, which is ejected as a photoelectron with kinetic energy equal to the photon energy minus the binding energy, leaving the atom ionised. Stage two: an outer-shell electron drops into the K-shell vacancy, releasing either a characteristic x-ray or an Auger electron. The interaction probability is proportional to Z cubed over E cubed and requires the photon energy to exceed the binding energy. Photoelectric effect: photon absorbed, then inner-shell vacancy filled + incident photon (hν) photoelectron KE = hν − Eb vacancy characteristic x-ray or Auger electron 1 · incident photon absorbed K-shell electron ejected, atom ionised 2 · outer electron fills the vacancy characteristic x-ray or Auger electron emitted Probability ∝ Z³ / E³ — greatest at low photon energy and high atomic number (Z). Occurs only when hν ≥ binding energy Eb; K, L or M electrons can be ejected.
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