James Franck

Even before the first World War, scientists James Franck and Gustav Hertz performed tests on Mercury atoms by bombarding them with electrons and measuring the energy changes resulting from the collisions. This data then was added to Nils Bohr’s theory “that an atom can absorb internal energy only in precise and definite amounts.”[i] It was not until many years later in 1921 that Otto Hahn and Lise Meitner officially developed the idea, along with Enrico Fermi and Emilio Segre, of bombarding the nucleus of a radioactive element with neutrons and measuring the heat energy given off as the nucleus splits. As a result, Hahn and Meitner, wrote a book with Fritz Strassmann about this concept, and in this book they argued that a few pounds of radioactive uranium had the explosive power of thousands of pounds of dynamite.
 
[i] Simkin, John. "Manhattan Project." Spartacus Educational. N.p., n.d. Web. 12 May 2011. <http://www.spartacus.schoolnet.co.uk/USAmanhattan.htm>.

Gustav Hertz

This was the beginnings of the atomic bomb and in January of 1939, a physics conference took place in Washington to discuss the possibility of producing an atomic bomb. It was here that the power of the bomb was discussed, not only in a physical sense, but rather whoever owned the atomic bomb had the power to “blackmail” all the other countries. Shortly after this meeting, President Roosevelt received a letter written by Albert Einstein, Leo Szilard, and Eugene Wigner telling FDR of the nuclear research that had been going on in Europe before they fled to the US.[i]

[i] Simkin

Albert Einstein