Joseph Rotblat (1908-2005) was a British-naturalized Polish physicist and 1995 Nobel Peace Prize winner.
Rotblat joined British physicist James Chadwick to work on the atomic bomb at Los Alamos in 1944. Rotblat was opposed to using the bomb or using science to develop such a weapon. He left the Manhattan Project, ostensibly on grounds of conscience, in late 1944 when it became clear Germany was not close to developing an atomic bomb. Rotblat was not allowed to reenter the United States until 1964 because of an accusation of spying for the Soviet Union.
Rotblat was born in Warsaw, Poland. After World War I he worked as a domestic electrician. He won a place in the physics department of the Free University of Poland, despite no formal education. He discovered that neutrons were emitted during the fission process, and went to Liverpool in 1939 to work with James Chadwick.
Rotblat returned home to Poland and left days before the outbreak of World War II, though his wife was left in Poland and died during the Holocaust in a concentration camp. It was also during this period he realized his research could be used for the atomic bomb. He continued his research because of the rise of Nazi Germany, and wanted Britain to have a deterrent if they developed a bomb.
After World War II, Rotblat worked at the University of Liverpool as a senior lecturer and acting director of research in nuclear physics, and naturalized as a British subject. He became interested in the medicinal and biological uses of radiation, and turned his scientific research towards areas that he believed would help society.
Rotblat developed an interest in nuclear fallout, and it became the primary focus of his research. He also became a prominent critic of the nuclear arms race and signed the Russell-Einstein Manifesto in 1955, which highlighted the dangers of nuclear weapons and called for world leaders to seek peaceful resolutions to international conflict. Forty years later, Rotblat was awarded the Nobel Peace Prize along with the Pugwash Conferences on Science and World Affairs "for their efforts to diminish the part played by nuclear arms in international politics and, in the longer run, to eliminate such arms."