Position sensing with magic gas mixture in the transition region from the proportional to the self-quenching streamer mode

Using a single-wire gas counter filled with magic gas mixtures, position sensing was performed in the region of the transition from the proportional to the self-quenching-streamer (SQS) mode. The gas mixtures used were Ar-iso-C₄H₁₀-Freon-13B1, known as the original magic gas mixture, and Ar-CH₄-Freon-13B1. Both mixtures were used with different concentrations of Freon 13B1, i.e. 0, 0.15, 0.45, 0.90 and 1.1%. It is shown that by adding a small amount of Freon vapor, the generation of the SQS mode becomes more stable. The iso-C₄H₁₀-based gas is shown to be more stable with respect to high anode voltage than the CH₄ based gas