Channeltron efficiency for counting of H+ and H− at low energy

The counting efficiency of a channel electron multipier is measured for H+ and H− impact with the input of the Channeltron grounded and for impact energies between 0.3 and 5 keV. The counting efficiency is found to be about 30% greater for H− than for H+ at energies below 1 keV. This difference and an observed difference between H− and H+ in the variation of counting efficiency across the Channeltron opening are attributed to the surface potential of the Channeltron near the opening, which can accelerate or decelerate the incident particles.