Photo from the Nobel Foundation archive.
Kai M. Siegbahn
The Nobel Prize in Physics 1981
Born: 20 April 1918, Lund, Sweden
Died: 20 July 2007, Ängelholm, Sweden
Affiliation at the time of the award: Uppsala University, Uppsala, Sweden
Prize motivation: "for his contribution to the development of high-resolution electron spectroscopy."
Prize share: 1/2
According to quantum physics principles, the electrons in atoms and molecules have defined energy levels. Albert Einstein's theory of the "photoelectric effect" says that a light particle (photon) can liberate an electron from an atom if it has sufficient energy. In the 1950s Kai Siegbahn developed methods for achieving highly accurate measurements of energy levels in atoms by irradiating them with photons and measuring the energy of the electrons emitted using the photoelectric effect.