Cosmogenic dating methods


If a sample is exposed at the surface for a time, no matter what the production rate or how long the exposure, the concentrations of the two nuclides conform to the production ratio.Then if you bury the sample deeply enough to stop new nuclide production, inventories of both nuclides (or at least one of the nuclides, if the other is stable) decrease due to radioactive decay.However, most of them are feasible and should be tried.The general concept of cosmogenic-nuclide burial-dating is that one has a pair of cosmogenic nuclides that are produced at a fixed ratio in some rock or mineral target, but have different decay constants.

I say “theoretically” a lot below — because mostly no one has done any of these things.The final ingredient we need is an estimate of the uncertainty in the production ratios of these nuclides.This is hard to estimate in a general way — it depends on the rock or mineral in question and its composition — so for purposes of the following discussion I’ll assume that we know these ratios accurately (however, this is a major issue for some nuclide pairs).I use the measurement uncertainties for the other nuclides as discussed above, assume no geologic uncertainty, and assume we know the production ratios accurately.This yields the following burial age-uncertainty relationship for the six nuclide pairs we are considering: Here is the same plot with a different axis, focusing on the Pleistocene: OK, what do we learn from this?Of these, Ne-21 is stable, so there is no uncertainty in its half-life. The following plot shows the concentration-measurement uncertainty relationship for all the Al-26 and Be-10 concentrations I could assemble from readily available data.

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