A Compton telescope (or Compton camera) is a type of gamma-ray telescope used for the photon-energy range of roughly 1-30 MeV. The term reflects the presumption that Compton scattering will occur to assist in detecting a photon. A common design uses a sequence of two detectors, one to sense Compton scattering of the incoming gamma ray photon, and the second to sense the already-scattered photon which will have a somewhat-lower photon energy. In both cases, the photon passes through a scintillator consisting of a material that will respond by producing EMR in/near the visiblelight band, in turn measured by photon-detection devices, photomultiplier tubes or photodiodes. The two events are detected through multiple detectors, offering a number of measurements based on energy and time, from which the direction and energy of the incoming photon can be worked out to substantial degree. The direction determination is somewhat degenerate (randomly from anywhere on the edge of a circle in the celestial sphere) so gamma-ray bursts with multiple photons offer triangulation to yield an angular resolution often a good bit better than a degree.
At higher photon energy (above 30 MeV), other types of detectors are used.