Near 100% Efficiency Ion Detector for Use with Quadrupole Mass Filter

Abstract
A 14‐stage Ag‐Mg Allen type electron multiplier is used as an ion detector with a large exit aperture (5 cm diam) quadrupole mass filter. A simple lens system provides sufficient focusing on the first dynode of the multiplier to insure near 100% ion collection and extremely stable detection. A pulse height distribution for single ion impacts closely similar to that expected using Poisson statistics is obtained. Arguments as to the system's efficiency as well as details of the construction of the multiplier are given.