Effective ionization coefficients, electron drift velocities, and limiting breakdown fields for gas mixtures of possible interest to particle detectors

摘要

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, CO(sub 2), and CF(sub 4), the binary gas mixtures CO(sub 2):Ar (20: 80), CO(sub 2):CH(sub 4) (20:80), and CF(sub 4):Ar (20:80), and the ternary gas mixtures CO(sub 2):CF(sub 4):Ar (10:10:80) and H(sub 2)O: CF(sub 4):Ar (2:18:80). Addition of the strongly electron thermalizing gas CO(sub 2) or H(sub 2)O to the binary mixture CF(sub 4):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 (= or >) 50 (times) 10(sup (minus)17) V cm(sup 2). The increase in (bar a)/N, even though the electron energies are lower in the ternary mixture, is due to the Penning ionization of CO(sub 2)(or H(sub 2)O) 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.