Design Considerations for a High Spatial Resolution Positron Camera with Dense Drift Space MWPC's

A multiplane Positron Camera is proposed, made of six MWPC modules arranged to form the lateral surface of a hexagonal prism. Each module (50×50 cm2) has a 2 cm thick lead-glass tube converter on both sides of a MWPC pressurized to 2 atm. Experimental measurements are presented to show how to reduce the parallax error by determining in which of the two converter layers the photon has interacted. The results of a detailed Monte Carlo calculation for the efficiency of this type of converter are shown to be in excellent agreement with the experimental measurements. The expected performance of the Positron Camera is presented: a true coincidence rate of 56000 counts/s (with an equal accidental coincidence rate and a 30% Compton scatter contamination) and a spatial resolution better than 5.0 mm (FWHM) for a 400 μCi point-like source embedded in a 10 cm radius water phantom.