The Technology

A HIDAC consists of a Multiwire Proportional Chamber (MWPC) with the provision of laminated cathodes containing interleaved lead and insulating sheets and mechanically drilled with a dense matrix of small holes. Ionisation resulting from photons interacting with the lead is trapped by, amplified in, and extracted from, the holes by a strong electric field into the MWPC. On arrival at an anode wire, further avalanching occurs. Coordinate readout may be obtained from orthogonal strips on the cathodes. The result is precise, two dimensional localisation of the incident gamma-rays. Every hole on the cathodes acts as an independent counter. By stacking these HIDACs, millions of these counters are integrated to form a large-area radiation camera with a high spatial resolution.