High efficiency gamma converters and their application in a MWPC positron camera

Honeycomb structured lead γ-ray converters have been developed and coupled with Multiwire Proportional Chambers to produce a position-sensitive hybrid detector for spatial localization of MeV range γ rays. Two such detectors operated in time coincidence mode function as a large-area large-solid-angle positron camera. The sensitivity of the camera system is measured to be 1600 counts/min-μCi, corresponding to a detection efficiency of 5.5 percent per detector. Images of phantoms and clinical objects are obtained by using the back-projection reconstruction method, and the results demonstrate the tomographic capability of such a positron camera system. A design analysis of the γ converter is presented, the detection efficiencies of converters of various dimensions are measured, and the results agree quite well with calculation. Further improvements in converter efficiency can be expected with modifications in the converter designs based on the concepts of enhanced surface area and uniformity of electron extraction field. The new converters under consideration are made of small-diameter high-lead-content lead glass tubing made conductive by hydrogen reduction treatment