How Scientific Chance and a Little Luck Helped Usher in the Nuclear Age
via Smithsonian
It is impossible to overstate the importance of this accidental discovery. The work that Fermi subsequently led to exploit this revelation, culminating in the development of the first nuclear chain reaction on December 2, 1942 in Chicago, was based entirely on the “slow neutron” effect. The graphite bricks that formed the structure of the first atomic pile served as a moderator to slow down the neutrons emitted from the uranium slugs embedded throughout the pile, enhancing the probability of fission. Not only are all nuclear reactors based on this effect; it was an essential aspect of fission research that led, inexorably, to the development of nuclear weapons.