  The Precision Reactor Oscillation and Spectrum (PROSPECT) Experiment is a
reactor neutrino experiment designed to search for sterile neutrinos with a
mass on the order of 1 eV/c$^2$ and to measure the spectrum of electron
antineutrinos from a highly-enriched $^{235}$U nuclear reactor. The PROSPECT
detector consists of an 11 by 14 array of optical segments in $^{6}$Li-loaded
liquid scintillator at the High Flux Isotope Reactor in Oak Ridge National
Laboratory. Antineutrino events are identified via inverse beta decay and read
out by photomultiplier tubes located at the ends of each segment. The detector
response is characterized using a radioactive source calibration system. This
paper describes the design, operation, and performance of the PROSPECT source
calibration system.
