THE MICROBALL - DESIGN, INSTRUMENTATION AND RESPONSE CHARACTERISTICS OF A 4-PI-MULTIDETECTOR EXIT CHANNEL-SELECTION DEVICE FOR SPECTROSCOPIC AND REACTION-MECHANISM STUDIES WITH GAMMASPHERE

A 4 pi multidetector light-charged particle and light fragment detecti on spectrometer is described. It consists of 95 CsI(T1) a scintillator s closely packed to cover the angular range 4.0 degrees-172 degrees, a rranged in 9 rings with increasing forward segmentation. The device is optimally designed to be used in conjunction with Gammasphere. The sc intillator light is collected by silicon photodiodes that provide high quantum efficiency and minimal mass. The signals are processed throug h a charge sensitive preamplifier followed by a slow shaper. Particle identification for H-1,H-2,H-3, He-3,He-4 ions and Li, Be and B ions i s accomplished by pulse shape discrimination. The geometry, constructi on, energy calibration, gain stability, associated integrated electron ics and the data acquisition system are discussed. The capabilities of this spectrometer as a channel selecting device in conjunction with G ammasphere are discussed. A second version of the device with thicker scintillators, that can stop more energetic charged particles and is u seful for reaction mechanism studies, is also described.