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Published: 1991

Total Pages: 8

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We have measured the gas-density, N, normalized effective ionization coefficient, {bar a}/N, and the electron drift velocity, w, as a function of the density-reduced electric field, E/N, and obtained the limiting, (E/N){sub lim}, value of E/N for the unitary gases Ar, CO2, and CF4, the binary gas mixtures CO2:Ar (20: 80), CO2:CH4 (20:80), and CF4:Ar (20:80), and the ternary gas mixtures CO2:CF4:Ar (10:10:80) and H2O: CF4:Ar (2:18:80). Addition of the strongly electron thermalizing gas CO2 or H2O to the binary mixture CF4:Ar (1) cools'' the mixture (i.e., lowers the electron energies), (2) has only a small effect on the magnitude of w(E/N) in the E/N range employed in the particle detectors, and (3) increases {bar a}/N for E/N ≥ 50 × 10−17 V cm2. The increase in {bar a}/N, even though the electron energies are lower in the ternary mixture, is due to the Penning ionization of CO2(or H2O) in collisions with excited Ar* atoms. The ternary mixtures -- being fast, cool, and efficient -- have potential for advanced gas-filled particle detectors such as those for the SCC muon chambers. 17 refs., 8 figs., 1 tab.