Fast gas mixtures for gas-filled particle detectors

Based on knowledge of the electron scattering cross sections at low electron energies, combinations of binary and tertiary gas mixtures have been discovered for which the electron energies and the overall scattering cross sections that correspond to these are reduced, resulting in an increase in the drift velocity, w, of the electrons in the gas mixture for a range of E/P (pressure-reduced electric field) values. Several such mixtures of argon (Ar), carbon tetrafluoride (CF₄) and acetylene (C₂H₂) will be described that provide much faster response in gas-filled detectors compared to P-10 (90% Ar + 10% CH₄) over a wide and convinient range of E/P values. The w(E/P) for CF₄(100%), Ar(80%) + CF₄(20%), Ar(80%) + C₂H₂(20%), Ar(80%) + C₂H₂(10%) + CF₄(10%) are respectively, ∼15 × 10⁶, ∼12 × 10⁶, ∼5 × 10⁶ and ∼9 × 10⁶ cm s^-1 at E/P values of, respectively, ∼6, 0.8-1.5, 0.5-4 and 0.8-3.5 V cm^-1 torr^-1. Measurements with a conventional proportional counter showed that although the energy resolution of the Ar/CF₄ mixtures compares unfavorably with the energy resolution of P-10, that of the C₂H₂-containing binary and tertiary mixtures compares very favorably.