Radiocarbon dating of pollen by accelerator mass spectrometry

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The original, and best known, application of AMS is radiocarbon dating, where you are trying to detect the rare isotope A nuclear particle accelerator consists essentially of two linear accelerators joined end-to-end, with the join section (called the terminal) charged to a very high positive potential (3 million volts or higher). Injecting negatively charged carbon ions from the material being analysed into a nuclear particle accelerator based on the electrostatic tandem accelerator principle. The negative ions are accelerated towards the positive potential.

At the terminal they pass through either a very thin carbon film or a tube filled with gas at low pressure (the stripper), depending on the particular accelerator.

A small sample size may or may not be a decisive advantage in a particular case, depending on the task and the nature of the sample material.Collisions with carbon or gas atoms in the stripper remove several electrons from the carbon ions, changing their polarity from negative to positive. The positive ions are then accelerated through the second stage of the accelerator, reaching kinetic energies of the order of 10 to 30 million electron volts. This problem is solved in the tandem accelerator at the stripper –if three or more electrons are removed from the molecular ions the molecules dissociate into their component atoms. The kinetic energy that had accumulated up to now is distributed among the separate atoms, none of which has the same energy as a single C from the more intense "background" caused by the dissociated molecules on the basis of their kinetic energy.Accelerating the ions to high energy has one more advantage.We are attempting to resolve whether this is due to contamination of the pollen or the presence of significant quantities of old reworked pollen.Pollen dates from lake sediments associated with Mazama Ash were consistent with other published ages; however, replicate dates on pollen samples from above the ash were consistently older than the surrounding sediment.

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