Segrè was born in Tivoli, Italy, on February 1, 1905. He entered the University of Rome expecting to major in engineering. But he encountered Enrico Fermi there and decided to change his major to physics, a field in which he obtained his Ph.D. in 1928. After graduation, he served a year in the Italian army and then continued his academic career at Rome, in Hamburg (with Otto Stern) and in Amsterdam (with Pieter Zeeman). Segrè was appointed to the faculty at Rome in 1932 and then became director of the physics laboratory at the University of Palermo in 1936.

Segrè's earliest research was in the field of atomic physics and spectroscopy. He studied the so-called "forbidden" spectral lines and a variation of the Zeeman effect. He also became interested in the use of neutrons to bombard elements. He attacked the problem of element number 43, the lightest element still...