Designing Modular Multi-Wire 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. To operate the chamber 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 between the wires, which are spaced 3mm apart. This task is not trivial, as the electric field strength inside the chamber will exceed 4 million volts per centimeter near the anode wires. This region of high field strength is critical to avalanche formation and is based in the Paschen theory for breakdown voltages. After a redesign of the original chamber we were able to keep the anode wires at a stable high voltage, specifically by designing a custom circuit board using the CAD program Eagle.