Quantum Efficiency Measurements of Windowless Electron Multipliers to Heavy High Energy Particles

Measurements of quantum efficiency to heavy charged particles, in particular to the proton, in the range of 5 to 2 MeV were made with windowless electron multipliers Qn cathodes of beryllium oxide and aluminum oxide. The effects of oxide thickness on quantum efficiency were determined and some qualitative explanations have been made based on the simple ionization process and escape probability of produced electrons. Using a Van de Graaff accelerator at beam currents of lnA to 5nA, precisions of measurement of better than 10% were obtainable with six different cathodes: three different thicknesses of BeO and three of Al2O3 respectively.