What Albert Einstein Invented.

The Atomic bomb

Please don't build one at home. On August 2nd 1939, just before the beginning of World War II, Einstein wrote to then President Franklin D. Roosevelt. Einstein and several other scientists told Roosevelt of efforts in Nazi Germany to purify U-235 with which might in turn be used to build an atomic bomb. It was shortly thereafter that the United States Government began the serious undertaking known only then as the Manhattan Project. Simply put, the Manhattan Project was committed to expedient research and production that would produce a viable atomic bomb.

The making of the Atomic Bomb

The most complicated issue to be addressed in making of an atomic bomb was the production of ample amounts of "enriched" uranium to sustain a chain reaction. At the time, uranium-235 was very hard to extract. In fact, the ratio of conversion from uranium ore to uranium metal is 500:1. Compounding this, the one part of uranium that is finally refined from the ore is over 99% uranium-238, which is practically useless for an atomic bomb. To make the task even more difficult, the useful U-235 and nearly useless U-238 are isotopes, nearly identical in their chemical makeup. No ordinary chemical extraction method could separate them; only mechanical methods could work.
A massive enrichment laboratory/plant was constructed at Oak Ridge, Tennessee. Harold Urey and his colleagues at Columbia University devised an extraction system that worked on the principle of gaseous diffusion, and Ernest Lawrence (inventor of the Cyclotron) at the University of California in Berkeley implemented a process involving magnetic separation of the two isotopes.
Next, a gas centrifuge was used to further separate the lighter U-235 from the heavier, non-fissionable U-238. Once all of these procedures had been completed, all that needed to be done was to put to the test the entire concept behind atomic fission ("splitting the atom," in layman's terms).