The OPAL Barrel Lead-Glass Calorimeter |
The barrel lead glass calorimeter, consists of a cylindrical array of 9440 lead glass blocks of 24.6 radiation lengths, located at a radius of 2455 mm, outside the magnet coil, covering the full azimuthal angle and |cos(theta)| < 0.82. The calorimeter is instrumented with magnetic field tolerant phototubes.
The logitudinal axes of the lead glass blocks point towards the interaction regoin to minimize the probability of a particle traversing more than one block. However, the blocks are tilted slightly from a perfectly pointing geometry to prevent neutral particles from escaping through the gaps between the blocks. In the z direction, the calorimeter is segmented into 59 blocks. In the phi direction, the calorimeter is segmented equally into 160 blocks.
Here you can see an image of the lead glass.