Some studies of multi-wire proportional chambers

Abstract

A study has been made of the displacement of sense wires in large multiwire proportional chambers, and methods are investigated to counteract this. A sense wire support which creates the minimum of dead-space while keeping the wires absolutely stationary is found to be a thin melinex strip stretched tightly across the wires. A brief review of some of the characteristics of transition radiation is then made; the application of the multiwire proportional chamber to detection of this radiation is described in the context of a pulse shape discrimination process developed for this purpose. Experiments with an X-ray and beta-particle source show that the technique should be capable of discriminating between an X-ray and a charged particle from an X-ray pulse superimposed upon a particle pulse. The discrimination process is used with 1.5 GeV electrons end pions traversing a 250 layer melinex stack and a block of plastic foam, the detector being an argon/methane filled proportional chamber. A maximum electron detection efficiency of M.B% is achieved, together with a maximum rejection ratio for non-radiating pions of 2.8.A further experiment with horizontal cosmic ray muons traversing a polyurethane foam radiator, and using a large 60cm x 30cm active area proportional chamber, yields a transition radiation photon flux of 0.023 per particle which is in good agreement with that calculated from the known horizontal muon spectrum and transition radiation theory.