A device for detecting high-energy X-rays, gamma rays, and cosmic rays, similar to a scintillation counter; the name is short for phosphor sandwich. It consists of a sandwich of two crystals of phosphorescent material which scintillate in response to incoming photons and cosmic rays. The scintillations produced within the crystals are fed to a photomultiplier tube where they are converted into an electric current. The responses of the different crystals can be used to measure the energies of the incoming X-ray and gamma-ray photons or other particles such as helium nuclei (alpha particles) or electrons (beta particles).