You can be forgiven for never hearing about The Franck Report that was issued on 11th June 1945, it was kept highly secret at the time and is one of those many WWII documents whose un-censored versions have only become public several decades later. The Franck Report was a document signed by several prominent nuclear physicists who had been working on the development of an atomic bomb recommending that the United States not use the atomic bomb as a weapon to prompt the surrender of Japan in World War II.
This entry in our 1945 timeline provides the reader with an easy explanation of the nuclear fission process that underlies the so-called “atom” bomb and a short summary of the history of the secret Manhattan Project which produced the two bombs that were dropped on Hiroshima and Nagasaki in August 1945 (which events will be described on those dates in this timeline).
It was German physicists who first discovered, in December 1938, that one could force a uranium atom to split into two much smaller atoms by bombarding it with a moving neutron. The smaller atoms have kinetic energy and the other products of this fission process are 2 or 3 free neutrons and a lot of energetic photons, these fragments heat up the bulk material. If there are more uranium atoms close by the free neutrons will cause them to split if they hit them, and if enough uranium is assembled in one place, or if the escaping neutrons are sufficiently contained, then these freshly emitted neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place. A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. This chain reaction of so-called fissile material produces lots of energy and it became obvious to the European physics community, both those physicists who stayed in Germany, and those European physicists who fled to the USA and the UK to avoid being persecuted or killed by the Nazis, that it would be relatively straight forward to make an “atomic” bomb based on the fission of uranium.
An atomic bomb design was relatively simple. When you bring together a sufficient amount of fissile material,