Gamma-Ray Detection with Pbo Glass Converters in Mwpc: Electron Conversion Efficiency and Time Resolution

The development of glass tube converters for efficient gamma-ray detection in multi-wire proportional chambers (MWPC) has led to an investigation of the improvement of conductivity on glass surfaces and to an investigation of gas mixtures which will improve on the electron conversion efficiency and electron transit time within the tubes. Efforts to establish uniform electric field lines within small diameter tubes has resulted in an improved H2 reducing treatment. For a 2cm thick converter made of glass tubing (0.9 mmID;1·10 mmOD) the electron conversion efficiency ¿ was measured to be 9.0% and 10.4% at 511 keV, using Ar mixtures containing 10% CF4 and 30% isobutane, respectively. The effects of gas mixtures on ¿ and on ¿, the mean transit time on conversion electrons within the converter, and the projection of these results to the performance of a modified MWPC positron camera are presented.