Robert Lyste Thornton was a Canadian-American physicist who oversaw the constuction and operation of the Beta calutron electromagnetic separation Plant in Oak Ridge, Tennessee during the Manhattan Project.
Thornton joined the Lawrence Radiation Laboratory at the University of California at Berkeley in 1933 and worked with Ernest Lawrence on the construction of several cyclotrons. In 1940, Thornton left Berkeley to help build a cyclotron at Washington University in St. Louis, where he also taught as an associate professor of physics.
Thornton returned to Berkeley in 1942 when the Radiation Laboratory undertook the electromagnetic isotope separation endeavor for the Manhattan Project. Lawrence assigned him the job of developing the massive calutron plant at Oak Ridge, a gigantic array of modified cyclotrons adapated to separate uranium isotopes. In 1943, Thornton became assistant director of the Process Improvement Division of the Tennessee Eastman Corporation at Oak Ridge.
In 1945, Thornton led construction of the 184-inch cyclotron at Berkeley. After the war, he was appointed Professor of Physics and remained there for the next twenty-seven years.