History of Nuclear Weapons - Physics and Politics in The 1930s

Physics and Politics in The 1930s

See the main articles at History of physics, Nazi Germany and World War II.

In the first decades of the 20th century, physics was revolutionised with developments in the understanding of the nature of atoms. In 1898, French physicists Pierre Curie and Marie Curie had discovered that pitchblende, an ore of uranium, contained a substance—which they named radium—that emitted large amounts of radioactivity. This raised hopes among scientists and laymen that the elements around us could contain tremendous amounts of unseen energy, waiting to be harnessed.

In 1934 the idea of chain reaction via neutron was proposed by Leó Szilárd, who patented the idea of the atomic bomb (British patent 630,726). The patent was assigned by him to the Admiralty (the controlling organisation for Britain's Royal Navy) in 1936, this 'sleight of hand' being necessary to prevent wider publication of the idea, as an Admiralty patent could be covered by the Official Secrets Act. In a very real sense, Szilárd was the father of the atomic bomb academically.

In 1934, French physicists Irène and Frédéric Joliot-Curie discovered that artificial radioactivity could be induced in stable elements by bombarding them with alpha particles, and in the same year Italian physicist Enrico Fermi reported similar results when bombarding uranium with neutrons.

In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting they had detected the element barium after bombarding uranium with neutrons; Lise Meitner and her nephew Otto Robert Frisch correctly interpreted these results as being nuclear fission. Frisch confirmed this experimentally on January 13, 1939.

Even before it was published, Meitner’s and Frisch’s interpretation of the work of Hahn and Strassmann crossed the Atlantic Ocean with Niels Bohr, who was to lecture at Princeton University. Isidor Isaac Rabi and Willis Lamb, two Columbia University physicists working at Princeton, heard the news and carried it back to Columbia. Rabi said he told Fermi; Fermi gave credit to Lamb. Bohr soon thereafter went from Princeton to Columbia to see Fermi. Not finding Fermi in his office, Bohr went down to the cyclotron area and found Herbert Anderson. Bohr grabbed him by the shoulder and said: “Young man, let me explain to you about something new and exciting in physics.”

It was clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On January 25, 1939 an experimental team at Columbia University conducted the first nuclear fission experiment in the United States in the basement of Pupin Hall. The team members were Herbert L. Anderson, Eugene T. Booth, John R. Dunning, Enrico Fermi, G. Norris Glasoe, and Francis G. Slack.

As Germany occupied Czechoslovakia in 1938 and then the German army marched into Poland in 1939, beginning World War II, many of Europe's top physicists had already begun to flee from the imminent conflict. Scientists on both sides of the conflict were well aware of the possibility of utilizing nuclear fission as a weapon, but at the time no one was quite sure how it could be done. In the early years of the war, physicists abruptly stopped publishing on the topic of fission, an act of self-censorship to keep the opposing side from gaining any advantage.