Enrico Fermi’s Discovery of Neutron-Induced Artificial Radioactivity: A Case of “Emanation” from “Divine Providence”

We reconstruct Enrico Fermi’s remarkable discovery of neutron-induced radioactivity in March 1934 with a focus on the experimental apparatus he used, such as the original neutron sources preserved in Italy and abroad. Special attention is paid to the role of the Radium Office of the Institute of Public Health in Rome in providing to Fermi the “radium emanation” (Radon-222) used to make his radon-beryllium neutron sources. This particular angle of investigation allows us to make a full reconstruction of what Fermi actually realized in his laboratory, to gain a better insight into his methodological choices, and, ultimately, to understand how special circumstances conspired to make the discovery of neutron-induced radioactivity possible.