HPC, the electromagnetic calorimeter in the barrel part of the DELPHI
detector, consists of 144 modules forming a cylinder with inner and outer
radius of 208 and 260 cm respectively. It is composed of several layers of lead
with regions of gas in between. The original particle interacts in the lead
giving rise to showers of particles that are detected in the gas due to the
ionisation they produce when traversing the gas volume. The total ionisation is
a measure of the energy of the original particle.
(1 out of 144 elements).