 Surface ionization detector

A surface ionization detector detects a neutral atomic beam by converting incident chemical atoms into ions on a hot surface. For suitable alkali metals, a heated tungsten surface can favor loss of an electron: the competing surface work function and atomic ionization energy make the efficiency strongly dependent on species, surface condition and temperature. An electric field then collects the resulting ions, producing an electric current or a count after amplification. A response therefore requires an efficiency measurement calibration; it is not automatically equal to the incident particle flux.

A 2002 imaging experiment used a tungsten-coated heated ribbon followed by a microchannel plate detector and a phosphor screen. It recorded where the arriving neutral chemical atoms struck, rather than just their total rate. The reported approximately $20\mu \mathrm{m}$ spatial resolution and roughly $50\%$ detection efficiency belong to that apparatus and its conditions, rather than to every surface ionization detector.^[ref]