Photoelectric effect

1. Introduction
Photoelectric effect is one of three possible interactions of γ radiation with the electron shell. Out of these three interactions has photon usually the lowest energy. It is a physical phenomenon, where electrons are ejected from matter (usually metal) due to absorption of electromagnetic radiation. Electrons emitted in this manner are then called photo electrons. Their emission is called photoelectric emission (photoemission).

2. History
As discoverer of photoelectric effect is regarded Heinrich Hertz, who noticed during his experiments with a spark gap generator, that sparkling UV radiation exposure facilitates the flashover, i. e. electric charge transmission between electrodes.

In 1899 Joseph John Thompson clarified the nature of photoelectric phenomenon decisively. Thompson identified electrons in the flow of negatively charged particles emitted from the metal.

The own nature of the phenomena described Albert Einstein in 1905 in detail and earned for that the Nobel Prize in Physics in 1921.

3. Physical description
The photoelectric effect occurs, when the entire energy of photon is passed on an electron in the electron shell of the absorbing material or a free electron (e.g. in metal). Part of the energy enables emission (work function Φ) of the electron from the atom, and the rest contributes to the electron's kinetic energy as a free particle (photo electron). The gamma photon perishes and his energy is taken over by the ionizing photo electron.

Einstein's photoelectric equation formulates the law of conservation of energy: $$h\cdot\upsilon=KE+\Phi$$.