Continuous FAB & LSIMS Ion Source

Exhibit no. 448

Fast atom bombardment (FAB) is an ionization technique in which a beam of neutral atoms strikes a surface. When fast moving ions are used instead of neutrals, the technique is referred as liquid secondary mass spectrometry or LSIMS. The ion source shown in the picture makes it possible to use cesium ion gun for LSIMS. When compared to xenon atom gun, the main advantage of the cesium ion gun operating at 25-35 kV is an increase of sensitivity in the high mass range. The ion source pressure remains lower because there is no gas admitted to the source region. The disadvantage is the high voltages employed, which require special measures to prevent electrical breakdowns.