Ion probe
An ion probe fires a narrow beam of ions at a polished sample and measures the isotopes knocked out of a tiny spot.
An ion probe, also called a secondary ion mass spectrometer or SIMS, aims a focused beam of ions, such as oxygen or caesium, at a polished sample. The beam sputters atoms from the surface, some of which become charged secondary ions. These are sent into a mass spectrometer and measured.
The great advantage is spatial resolution. An ion probe can analyse spots a few micrometres across, and the NanoSIMS version can map features smaller than a micrometre. This lets researchers measure isotopes within single chondrules, zones of a CAI, or individual presolar grains, without dissolving the sample.
Ion probes have transformed meteoritics. They revealed the variations in oxygen isotopes between minerals within CAIs, found magnesium-26 excesses from aluminium-26 in individual crystals and identified thousands of presolar silicate grains in situ. They are also used on returned samples from Ryugu, Bennu and comets, where every grain is precious and must be analysed with minimal loss.
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Level: Expert Advanced