The fundamental point in fabricating a chain reacting machine is of course to see to it that each fission produces a certain number of neutrons and some of these neutrons will again produce fission.

In a paper co-authored with Chen Ning Yang he speculated that pions might actually be composite particles. Fermi did important work in particle physics especially related to pions and muons and he speculated that cosmic rays arose through material being accelerated by magnetic fields in interstellar space. Fermi achieved first place in the classification of the entrance exam.

Through experiments inducing radioactivity with recently discovered neutrons Fermi discovered that slow neutrons were more easily captured than fast ones and developed a diffusion equation to describe this which became known as the Fermi age equation. He bombarded thorium and uranium with slow neutrons and concluded that he had created new elements for which he was awarded the Nobel Prize but the new elements were subsequently revealed to be fission products.