Secondary Ion Mass Spectrometry (SIMS)

A focused primary ion beam is used to sputter or erode a target. The energy of the primary ion beam, usually 10-20 keV is sufficient to knock atoms and fragments of material from the target and cause ionisation. These secondary ions can be electrostatically extracted and passed into a mass spectrometer. The SHRIMPs use a large magnetic sector for mass separation whereby an ion passing through the magnetic field will trace an arc of radius proportional to its mass. Hence mass separated ion beams can be passed on to a counting system to allow determination of elemental and isotope compositions of the target.