Stable Isotope Ratio
Definition
The ratio of a heavy to a light stable (non-radioactive) isotope of an element, expressed as delta (delta) in per-mil notation relative to a standard. For timber forensics the key ratios are delta-D, delta-18O, delta-13C, and 87Sr/86Sr.
- Notation
- Delta in per-mil relative to a standard
- Key timber ratios
- δD, δ18O, δ13C, 87Sr/86Sr
- Basis
- Heavy-to-light isotope ratio
- Application
- Geographic provenance
Common questions
Why does timber forensics use several isotope ratios together rather than just one?+
Each ratio responds to a different environmental driver, water source for δD and δ18O, photosynthetic pathway and climate for δ13C, and underlying geology for 87Sr/86Sr, so combining them narrows the plausible growth region far more than any single ratio could.
What does a per-mil delta value actually represent?+
It expresses how far a sample's isotope ratio deviates from an internationally agreed reference standard, in parts per thousand, which lets laboratories compare results across instruments and studies on a common scale.
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