Designing and Testing Modular Multiwire Proportional Chambers for Cosmic Ray Muon Detection

The Society of Physics Students (SPS) at Kennesaw State University is building a series of multi-wire proportional chambers as a tool to detect cosmic ray muons with the goal of doing muography on large structures. The chamber consists of two cathode plates that enclose an array of wires and is filled with an ionizing gas. A voltage difference of approximately 2kV must be applied between the wires and the cathodes. High energy muons that pass through the chamber ionize the gas, and the resulting free electrons then avalanche towards the anode wires in a cascade of secondary ionization. This avalanche induces a current in the anode which we will detect with amplifier electronics. The chamber must be able to hold 2kV without any current leakage, which was achieved by designing custom circuit boards in a CAD program. The electric field strength inside the chamber will exceed 3 million volts per meter near the anode wires. This region is critical to avalanche formation and is based in the Paschen theory for breakdown voltages. Presently, new prototypes are being tested with alpha and beta sources to better characterize the signals that the chambers will produce. Simulations are being run in Geant and ComSol to better understand and predict results.