Characteistics of Multiwire Proportional Chambers for Positron Imaging

We describe multivire proportional chambers (MWPC) designed for use in a positron camera for Nuclear Medicine applications. The coordinates of the two annihilation gamma rays are detected in the chamber by their interaction with thin lead converters placed on both faces of each chamber. In order to obtain reasonable efficiencies (10%) the lead converters have been made in a square honeycomb-like structure, which increases the effective surface area and also permits the application of a drift field to extract the electrons into the active area of the MWPC.