Photograph of the KTeV CsI Calorimeter

This photo shows the upstream face of the CsI electromagnetic calorimeter. The calorimeter consists of 3100 crystals, each 50 cm (27 radiation lengths) long. The inner crystals have a cross-section of 2.5 cm by 2.5 cm while the outer crystals are 5.0 x 5.0 cm. 80% of the crystals are actually pairs of 25 cm long crystals which have been glued together to form a single unit. The remaining 20% are single crystals. There are two 15 cm by 15 cm holes at the vertical midplane of the detector to allow the two neutral beams to pass through.