The Nobel Prize in Physics 1967
Hans Albrecht Bethe
Born: 2 July 1906, Strassburg (now Strasbourg), Germany (now France)
Died: 6 March 2005, Ithaca, NY, USA
Affiliation at the time of the award: Cornell University, Ithaca, NY, USA
Prize motivation: "for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars"
The discovery of fission, the splitting of a heavy nucleus, showed that large quantities of energy were liberated, an effect used e.g. in nuclear reactors. The liberated energy comes from the mass differences. Conversely, energy can also be liberated when light nuclei join to make a heavy one, fusion.
Hans Bethe showed in 1938 that fusion is the basis for the enormous energy flow from stars. He proposed two different processes, both of which result in that hydrogen nuclei fusion to helium nuclei.