Principles of radiometric dating

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Mass spectrometers detect atoms of specific elements according to their atomic weights.They, however, do not have the sensitivity to distinguish atomic isobars (atoms of different elements that have the same atomic weight, such as in the case of carbon 14 and nitrogen 14—the most common isotope of nitrogen).Radiometric dating methods detect beta particles from the decay of carbon 14 atoms while accelerator mass spectrometers count the number of carbon 14 atoms present in the sample.Both carbon dating methods have advantages and disadvantages.In mass analysis, a magnetic field is applied to these moving charged particles, which causes the particles to deflect from the path they are traveling.If the charged particles have the same velocity but different masses, as in the case of the carbon isotopes, the heavier particles are deflected least.Reference materials are also pressed on metal discs.These metal discs are then mounted on a target wheel so they can be analyzed in sequence.

When the samples have finally been converted into few milligrams of graphite, they are pressed on to a metal disc.Thanks to nuclear physics, mass spectrometers have been fine-tuned to separate a rare isotope from an abundant neighboring mass, and accelerator mass spectrometry was born.A method has finally been developed to detect carbon 14 in a given sample and ignore the more abundant isotopes that swamp the carbon 14 signal.After pretreatment, samples for radiocarbon dating are prepared for use in an accelerator mass spectrometer by converting them into a solid graphite form.This is done by conversion to carbon dioxide with subsequent graphitization in the presence of a metal catalyst.

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