Isotope Ratio Analysis
Definition
Measurement of relative abundances of two or more isotopes of an element to 0.01 to 0.5 percent precision. Lead ratios fingerprint the ore deposit a bullet was cast from, 87Sr/86Sr traces geographic origin, and 235U/238U anchors nuclear forensic attribution. Quadrupole ICP-MS reaches roughly 0.1 percent precision; multicollector sector instruments at BARC reach a few parts per million.
- Typical precision
- 0.01 to 0.5 percent
- Bullet lead use
- Fingerprints ore-deposit origin
- Provenance marker
- 87Sr/86Sr
- Instrument precision
- Quadrupole ICP-MS ~0.1%; MC sector instruments finer
Common questions
How does isotope ratio analysis differ from elemental composition analysis of a bullet?+
Elemental analysis (as in the retired bullet-lead comparison method) measures trace-element concentrations, which can vary within a single production batch. Isotope ratio analysis instead measures the ratio of lead isotopes, which reflects the geological origin of the ore and is far more stable within a source, giving a more defensible provenance signal.
Why does provenance work need instruments with such fine precision?+
Isotope ratios between different ore sources or geographic regions can differ by only a fraction of a percent, so distinguishing one source from another requires an instrument precise enough to resolve those small differences reliably, which is why multicollector sector instruments outperform standard quadrupole ICP-MS for this specific application.
Related terms
- Collision and Reaction Cell (CRC)
- A pressurised cell between the skimmer and the quadrupole, charged with helium for kinetic-energy-discrimination collision mode or with hydrogen, ammonia or oxygen...
- Inductively Coupled Plasma (ICP)
- An argon discharge sustained at 6000 to 10000 K by an RF coil at 27.12 MHz wrapped around a quartz torch. Argon...
- Optical Emission Spectrometry (OES)
- Detection arm in which excited atoms emit photons at characteristic wavelengths as they relax. A polychromator separates the light by wavelength and...
- Polyatomic Interference
- An ion formed in the plasma at the same nominal mass as a target analyte, for example argon-oxide on iron-56, argon-chloride on...
- Quadrupole ICP-MS
- Detection arm in which positive ions are extracted from the plasma through sampler and skimmer cones into a quadrupole mass filter that...