When was the nuclear bomb invented?

Answer 1

H. G. Wells' novel The World Set Free published in 1914 was the first usage of the term atomic bomb. He reasonably correctly estimated their energy release (based on Einstein's special relativity) but could not imagine that the energy could be released faster than was possible in chemical bombs, so his atomic bomb explosions took days to weeks instead of microseconds.

Leo Szilard invented the neutron chain reaction, which makes both atomic bombs and nuclear reactors possible in 1933 while living in London. He patented it in 1934 and when the patent (GB630726) was granted in 1936 he sold it to the British Admiralty who classified it to keep the information from the Nazis. The only problem was that no material was known at that time that would support a neutron chain reaction.

In 1939 a joint German and Swedish team in repeating an experiment performed originally in 1938 by Enrico Fermi (who had mistakenly decided that when he bombarded uranium with neutrons that he had made transuranic elements) determined that neutrons split the uranium atom into two smaller intensely radioactive atoms plus several neutrons. It was not necessary to see Szilard's classified patent to realize that uranium was the material that would support a neutron chain reaction. It took a little more research to identify that only the rare uranium-235 isotope (0.7%) would support a neutron chain reaction, not the plentiful uranium-238 isotope (99.3%).

The British did not declassify Szilard's patent until 1949, after the Soviet atomic bomb test.

Answer 2

The answer to this question is much more complex than you might imagine:

1. Leo Szilard invented the atomic bomb in 1933, in London while crossing a street.
2. Leo Szilard patented his atomic bomb in England in 1934.
3. Leo Szilard signed his patent over to the British Admiralty in 1936 to prevent the Nazis from getting access to it.
4. Otto Frisch discovered nuclear fission of Uranium-235 in 1938, while working in Berlin. This discovery made Szilard's invention practical.
5. Leo Szilard wrote a letter to FDR about the danger if the Nazis made an atomic bomb first and had Einstein sign it in 1940.
6. FDR formed a committee to study the issue of atomic weapons, authorizing a budget of $6000 for the study.
7. The committee's report recommended a project, which began in 1942 to build the bomb.
8. This project became the Manhattan Project, which built a complex industrial infrastructure to make the parts of the bomb. This cost over $2,000,000,000.
9. At least 4 bombs were available, in kit form by the summer of 1945. Three of these were detonated. The 4th kit never left the US and was returned to Los Alamos.