Large Aperture, High Efficiency Ion Detector

Abstract

A simple, highly efficient detector has been developed for negative ions that is similar to B. W. Ridley's for positive ions. The negative ions are accelerated to 10 keV, strike a Duralumin surface at 45° incident angle, and eject secondary electrons. These are in turn accelerated by 10 keV and focused crudely onto a plastic scintillator joined to an RCA 8575 photomultiplier tube. The detector has an entrance aperture of 5×5 cm, over which the sensitivity is uniform. The Duralumin surface requires no special preparation other than perfunctory initial cleaning, and the detector functions with excellent stability even in a rather poor vacuum (≈10⁻⁵ Torr). With appropriate voltage changes in the ion source the detector has been tested successfully for most of the positive alkali ions as well as the negative halogen ions F⁻, Cl⁻, Br⁻, and I⁻. The detector noise is a few counts per second at efficiencies exceeding 90% for all these ions, excluding grid losses.