My arrival in the United States coincided with the news of the discovery of nuclear fission. Taking inspiration from the fission of the uranium nucleus obtained by Otto Hahn and Fritz Strassman in December 1938, Lise Meitner and Otto Frisch demonstrated that by bombarding a nucleus of a heavy element with a neutron, the former split, releasing an enormous amount of energy according to the formula Einstein’s E=mc2.
In our experiments, we split the uranium core into two large chunks. We made the first fission without realising it.
The outbreak of the Second World War and the dangerous advance of Nazi fascism pushed a part of the international research towards using nuclear energy for military purposes.
In Germany, Werner Heisenberg, one of the most famous German physicists of the time, was working on developing a nuclear fission weapon. All the physicists who emigrated to the United States and I became alarmed. Albert Einstein wrote a letter to President Roosevelt to warn him of the danger of the probable construction by the Germans of a nuclear weapon that could lead Hitler to conquer the world.
Thus, President Roosevelt entrusted the army with the direction of the Manhattan Project for constructing fission bombs. The project involved the entire American physics community, and I played a crucial role, too. First, I worked in the laboratories of Columbia University in New York on creating a nuclear chain reaction. In 1942, we transferred our activities to the University of Chicago. We built the Chicago Pile One atomic pile in the underground gym of a stadium; it went into operation in December 1942. It was the world’s first autonomous nuclear fission reaction experiment. With a coded phone call, Nobel Prize winner Arthur Compton announced the success of the experiment to James Conant, president of the National Defense Research Committee:
“The Italian navigator has just landed in the new world.”
The story has also been told several times by my wife, Laura.
“One of the physicists gave Fermi a flask of Chianti: the gift was an indication of special respect for the country of the person who received it. Those present all drank, in silence, without toasts, then everyone put their signatures on the straw of the flask.”
1944, July 11th, I took American citizenship, and in September, I moved to the Los Alamos desert. In this centre, I made a fundamental contribution to the construction of the atomic bomb and remained tied to military secrecy until the war’s end.
“I learned not to ask questions. No longer what do you do today, nor how is work going… nor who are your collaborators?”
Once the conflict was over, it was time for new projects. I founded a new school in Chicago where I developed many research topics with my usual and well-known method: “Never do anything with greater precision than is strictly necessary”.
Many of my collaborators and students of that time became accomplished physicists and Nobel Prize winners.
I then became a consultant to the US government. I never favoured the use of nuclear energy for warfare. I then resumed regular contact with Italy, contributing to the relaunch of the research undertaken by Amaldi. 1954, November 28th, I died of cancer. I was 53 years old.