Accelerator Mass Spectrometry
Definition
A mass spectrometer fronted by a high-energy particle accelerator (typically a 500 keV to 6 MeV tandem). Counts individual carbon-14 atoms directly rather than waiting for them to decay. Needs only a milligram of carbon and a few hours of run time, against grams and weeks for conventional liquid scintillation. The modern global standard for radiocarbon dating, including for questioned documents.
- Accelerator energy
- About 500 keV to 6 MeV tandem
- Sample need
- A milligram of carbon
- Run time
- A few hours
- Contrast
- Grams and weeks for liquid scintillation counting
- Application
- Radiocarbon dating, including questioned documents
Common questions
Why does AMS need so much less sample than conventional counting?+
It counts individual carbon-14 atoms directly with a mass spectrometer instead of waiting to detect their radioactive decay, so it does not need a large sample to accumulate enough decay events.
How is AMS applied to questioned documents?+
It can date cellulose in paper, or measure bomb-pulse carbon-14 in ink or biological traces, to estimate when the material formed, which can support or contradict a claimed document date.
Is AMS destructive to the evidence being tested?+
It requires physically sampling and combusting a small portion of the material, so it is minimally but genuinely destructive, and the sampling location and size should be documented.
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