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 Aage Bohr. Their conversations during this period led to the development of a new conception of the atomic nucleus. At the time, physicists were trying to construct a model of the nucleus that would account for the forces acting between the protons and neutrons. Aage Bohr's father, the noted physicist Niels Bohr, had earlier suggested the analogy of a drop of liquid as one possible model. Bohr proposed that the nucleus vibrated and changed shape like a drop of liquid. Other possible explanations were suggested by scientists Maria Goeppert Mayer and J. Hans D. Jensen, who conceived of the nucleus as a series of onion-like layers or shells. According to this theory, the nucleons move independently in their own concentric orbits in shells. The forces are equal throughout the nucleus, creating a nucleus with a uniform spherical force field. The shell theory succeeded in describing the motion of the nucleons, but its assumption that the nucleus was a symmetrical sphere was proven wrong by later research showing that the electrical charge around the nuclei was not spherical. Rainwater would explain why. After attending a lecture by Charles H. Townes in 1949 on the inconsistencies of the two nuclear models, Rainwater came up with the idea that centrifugal forces within the nucleus might make the spherical shape around the nucleus more like an ellipsoid or football. In 1950, he published his hypothesis in a paper titled "Nuclear Energy Level Argument for a Spheroidal Nuclear Model."
Rainwater convinced Aage Bohr that his hypothesis was correct. After Bohr returned to Copenhagen, he and fellow Danish physicist Ben Mottelson developed a comprehensive theory of nuclear behavior, publishing their findings in 1952. The scientists used Rainwater's hypothesis to combine aspects of the liquid-drop model with the shell model, proposing that the collective action of the protons and neutrons made the surface of the nucleus act a like a drop of liquid, which could be deformed into a football-like shape if the outer shell of the nucleus was not filled with all the nucleons it could hold. It would then appear to oscillate and change its size. But if the outer shell of the nucleus had its complete number of nucleons, it appeared spherical.
While Bohr and Mottelson were publishing their theory, Rainwater was at work in the Nevis laboratory with a colleague, Val L. Fitch, observing X rays emanating from muons. His work revealed that the size of protons was being overestimated at the time. Other research by Rainwater focused on the properties of muons and their interactions with nuclei and advanced insight into the behavior of neutrons.
In 1975, Bohr, Mottelson, and Rainwater received the Nobel Prize for their discovery of the connection between collective motion and particle motion in atomic nuclei and for the development of the theory of the structure of the atomic nucleus based on this connection. The U.S. Atomic Energy Commission honored Rainwater in 1963, and the National Academy of Sciences elected him a member in 1968. In 1942, Rainwater married Emma Louise Smith and the couple had three sons and a daughter. Rainwater's interests included geology, astronomy, and classical music. Shortly after retiring in 1986, Rainwater died in Yonkers, New York.
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