Robert Nason Beck (March 26, 1928, in San Angelo, Texas – August 6, 2008, in Chicago, Illinois) was an American scientist and a pioneer in the field of nuclear medicine. Part of a University of Chicago team, he was the first to propose, in 1961, the use of the radioisotope technetium-99m to detect disease using Single Photon Emission Computed Tomography, a technique that is used an estimated 20 million times a year throughout the world. Beck also helped develop collimators for sharpening the images produced by gamma-ray scanners, and was referred to as 'Mr. Collimator' by colleagues.