How does a mass spectrometer help scientists date rocks and minerals?

A mass spectrometer is a critical instrument in geochronology that allows scientists to measure the age of rocks and minerals by determining the precise isotopic composition of a sample.1

The process generally involves the following steps:

• Ionization and Separation: A sample is vaporized in a vacuum, and its atoms are converted into a beam of charged ions. This beam passes through a strong magnetic field, which separates the ions into distinct beams based on their specific mass.1
• Measurement: The number of atoms in each beam is measured, often using a Faraday cup. By measuring the ratio of different isotopes—often using an artificially enriched isotope known as a "spike"—scientists can accurately calculate the amount of parent and daughter isotopes present, which reveals the sample's age.12
• Advanced Techniques: Modern methods include accelerator mass spectrometry for direct atom counting and the sensitive high-resolution ion microprobe (SHRIMP), which allows for the analysis of tiny mineral grains without chemical dissolution.2