During the period from 1966 to 1972 the physics research program at SLAC was based solely on fixed-target experiments carried out with the two-mile linac. Early experiments with this machine were the first to show that the constituents of the atomic nucleus, the proton and neutron, are themselves composed of smaller, more fundamental objects called quarks. This work was recognized by the award of the 1990 Nobel Prize in Physics to Jerome Friedman and Henry Kendall of MIT and Richard Taylor of SLAC.
Sources of polarized beams, in which the electrons' magnetic fields are aligned along the beam axis, were added to the SLAC linac in the 1970s. In 1978 the polarized electron beam was used in an experiment of exceptionally high precision that established a clear relationship between the familiar electromagnetic force and the so-called weak force that produces radioactive decay.
Work continues on a series of experiments exploiting the polarized beams with targets whose atoms are also polarized to produce a deeper understanding of the structure of the proton and neutron and their quark consituents. Experiments with other targets are aimed at understanding the behavior of quarks in the nuclei of heavy atoms.