Speakers
Description
We present the development of Thick Gaseous Electron Multiplier (THGEM) detectors designed for cosmic muon radiography. As a robust variant of Micro-Pattern Gaseous Detectors (MPGDs), THGEMs can offer excellent position resolution, durability and portability, making them highly effective in muography application. To serve as effective tracking detectors in muography, these devices must offer sub-millimeter position resolution, long-term stability, and high muon detection efficiency. Several prototypes of dimensions 4 cm $\times$ 4 cm and 10 cm $\times$ 10 cm were designed at SINP, and manufactured using standard PCB drilling and etching technology on double-clad, insulating materials at the local industries, and then tested in both single and double-stage configuration. In double-stage operation, lesser discharge rate and higher gains were achieved. To further enhance stability and suppress discharges, a dedicated post-fabrication treatment involving surface polishing, ultrasonic cleaning and conditioning was implemented. A maximum gain of approximately $7\times 10^3$ and $3.3\times 10^4$ in single and double-stage respectively could be achieved using Ar-CO2 (90:10) gas mixture while the maximum muon detection efficiency was found to be 99% and 99.5%. The position resolution of the prototype equipped with a readout plane consisting parallel strips of width of 350 μm and pitch of 450 μm was studied using a high precision 3-axis positioning system. It was used to scan the detector response by irradiating with an Fe55 source with 2 mm collimator. Event positions were reconstructed from strip charges using the Centre-of-Gravity method, yielding a best spatial resolution of 30 μm in both configurations. Furthermore, the impact of operating voltage and alternatively gain, on position resolution of both the configurations was evaluated for Ar-CO2 (90:10) and Ar-isobutane (95:5) gas mixtures. Experimental results were validated through Garfield++ simulations.