The Manhattan Project: Making the Atomic Bomb
Part II: Early Government Support
Scientists had concluded that enriched samples of uranium-235 were necessary for further research and that the isotope might serve as a fuel source for an explosive device; thus, finding the most effective method of isotope separation was a high priority. Since uranium-235 and uranium-238 were chemically identical, they could not be separated by chemical means. And with their masses differing by less than one percent, separation by physical means would be extremely difficult and expensive. Nonetheless, scientists pressed forward on several complicated techniques of physical separation, all based on the small difference in atomic weight between the uranium isotopes.