SASY Detector

A large solid angle detector array, SASY, has been constructed to observe photonuclear reactions on light nuclei. This detector consists of an array of 432 NaI(Tl) blocks (XTAL Box) surrounding the target (50<theta<140) and a forward wall of plastic scintillator bars 1.5 m by 1.5 m by 0.3 m thick followed by a wall of 173 lead glass blocks.

Plastic scintillator paddles in front of the forward wall and surrounding the target are used for charged particle identification. This system provides nearly complete coverage for pi⁰ detection and about 75% coverage for charged pions.

A gas Cerenkov detector in the downstream beam and an aerogel Cerenkov detector near the target at forward angles are used to suppress atomic pairs in the trigger. To increase the efficiency for detecting neutrons, a plastic scintillator array (the Neutron Barrel) with 32 azimuthal segments can be inserted between the target and the XTAL Box.