GASES OF POSSIBLE INTEREST TO SSC MUON DETECTORS

We have been exploring the development of multicomponent gas mixtures with optimal electron transport, gain, electrical and chemical properties of potential interest to the Superconducting Super Collider muon detectors focusing in particular on binary and ternary mixtures of Ar, N2, CO, CO2, CH4, CF4, NH3, and H2O. In this article, we report and discuss: (i) recent measurements of electron drift velocities as a function of the density-reduced electric field E/N for CO2/CF4, CO2/CH4, CO2/N2, CO/Ar, Ar/Si(CH3)4, NH3/CF4/Ar, CO2/CF4/Ar, and H2O/CF4/Ar mixtures, (ii) calculated values of the mean electron energy as a function of E/N for a number of unitary gases and the gas mixtures CO2/CF4, CO2/CH4, and CF4/Ar, and (iii) effective ionization coefficients as a function of E/N for Ar/CF4, Ar/CO2, CO2/CH4, and mixtures of Ar/CF4 containing CO2 or H2O. Addition of CO2 or H2O or NH3 to CF4/Ar causes electron "cooling" and increases the electron yield; the addition of H2O (or NH3) may, also, improve the detector aging performance. Mixtures of Ar/CF4 with CO2 or H2O appear promising. All results reported are for the case of zero magnetic field.