American physical chemist who proposed the gas diffusion process for separating uranium-235 from uranium-238 and in collaboration with the U.S. physicist Edwin Mattison McMillan (McMillan, Edwin Mattison) discovered the element neptunium.

After receiving a Ph.D. (1939) in nuclear physics from the University of California at Berkeley, Abelson worked as an assistant physicist (1939–41) in the department of terrestrial magnetism of the Carnegie Institution of Washington, D.C. There he began investigating a material that emitted beta rays (electrons) and that was produced by irradiating uranium with neutrons. After joining forces with McMillan, he proved the material to be a new element, later named neptunium.

During World War II Abelson worked with the Naval Research Laboratory in Washington, D.C. His uranium-separation process proved essential to the development of the atomic bomb. At the end of the war his report on the feasibility of building a nuclear-powered submarine gave birth to the U.S. program in that field.

In 1946 Abelson returned to the Carnegie Institution and pioneered in utilizing radioactive isotopes. As director of the Geophysics Laboratory of the Carnegie Institution from 1953 to 1971, he found amino acids in fossils, and he discovered fatty acids in rocks more than 1 billion years old. He was president of the Carnegie Institution from 1971 to 1978 and trustee from 1978. From 1962 through 1984 he was the editor of Science, the weekly publication of the American Association for the Advancement of Science. In 1987 Abelson was awarded the National Medal of Science.