Leo James Rainwater was born in Council, Idaho, to Edna Eliza Teague and Leo Jasper Rainwater. As a doctoral student at Columbia University in New York City, Rainwater studied under such notable physicists as Enrico Fermi and Edward Teller Edward Teller. In 1942 Rainwater was appointed a scientist in the Manhattan Project, thus delaying his thesis research in order to participate in the development of the atom bomb. Rainwater used the Columbia cyclotron particle accelerator to study the behavior of neutrons (uncharged elementary particles with a mass nearly equal to that of protons). In 1946 he received his Ph.D. and became a physics instructor at Columbia.

After World War II, Rainwater helped build an improved particle accelerator at the Nevis Laboratory at Columbia University. When the synchrocyclotron became operational in 1950, it enabled scientists to study other particles besides neutrons. During this time Rainwater shared an office with Danish physicist...