Anticoincidence Detector

Anticoincidence Detector is the first line of defense against the enormous charged particle background from cosmic ray primary and Earth albedo secondary electrons and nuclei.  It consists of segmented plastic scintillator tiles, read out by wave-shifting fibers and photo-multiplier tubes. The segmentation is designed to avoid the self-veto problem of EGRET at high energies while stilll providing high cosmic-ray rejection.