Hans Albrecht Bethe (born July 2, 1906), is an American physicist from Strassburg (then part of Germany, now Strasbourg, France).
Bethe studied physics at Frankfurt and obtained his doctorate from the University of Munich. He left Germany in 1933 when the Nazis came to power, moving first to England and in 1935 to the USA where he taught at Cornell University. He was the Director of the Theoretical Division at Los Alamos National Laboratory and participated at the most senior level in the World War II Manhattan Project that produced the first atomic weapons.
During 1935-1938, he studied nuclear reactions and reaction cross sections. This research was useful to Bethe in more quantitatively developing Niels Bohr's theory of the compound nucleus. In 1967, Bethe was awarded the Nobel Prize in Physics for his studies of the production of solar and stellar energy, stellar nucleosynthesis. He postulated that the source of this energy are thermonuclear reactionss in which hydrogen is converted into helium.
Bethe is noted for his theories on atomic properties.
During the '80s and '90s he campaigned for the peaceful use of nuclear energy. In 1995, at the age of 88, Bethe wrote an open letter calling on all scientists to "cease and desist" from working on any aspect of nuclear weapons development and manufacture.