VELOCITY AND ION SPECIES DEPENDENCE OF THE GAIN OF MICROCHANNEL PLATES

The gain of a detector with a microchannel plate as analogue amplifier was determined for H+, H-2+, N+, O+, NH2+, CH4+, NH3+, H2O+, C2H3+, N2+, CO+, C2H5+, NO+, S+, H2S+, Ar+, C3H5+, C3H7+, CO2+, C4H10+, Kr+ and Kr2+ ions With velocities from 1 x 10(5) to 3 x 10(5) m s-1. The velocity dependence of the gain can be approximated by a Parilis-Kishinevskii type relation. The gain for molecular ions can be calculated from the gain for the atomic ions with an addition law of the form gain = G0 SIGMA(i) n(i)a(i)upsilon arctan[b(i)(upsilon - upsilon0)] where G0 is a reference gain, n(i) is the number of atoms i in the molecule, a(i) and b(i) are characteristic coefficients for the atoms i, and v0 is the species-independent threshold velocity. The addition law does not hold for H-2+ ions.