Measurement of drift velocity and amplification coefficient in C2H2F4-isobutane mixtures for avalanche-operated resistive-plate counters

The knowledge of the transport and amplification parameters (drift velocity , first Townsend and attachment coefficients) of the gas mixtures used for avalanche-operated resistive-plate counters gives the possibility of better understanding the underlying physical processes of these detectors and of developing Montecarlo simulations of their behaviour. We present here a mea surement of the drift velocity nu(d) and of the amplification coefficient e ta in C2H2F4- isobutane mixtures. The ionization in the gas, contained in a 6 x 22 cm(2), 2 mm gap RPC, is obtained by means of a pulsed N-2 laser, vi a double-photon ionization. Results are presented for nu(d) and eta as a fu nction of the applied electric field. (C) 1999 Elsevier Science B.V. All ri ghts reserved.