3 assumptions of radiometric dating
The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate.This normally involves isotope ratio mass spectrometry.The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating can not be established.On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades.These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace.As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy.
This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles) and beta decay (electron emission, positron emission, or electron capture).Precision is enhanced if measurements are taken on multiple samples from different locations of the rock body.Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. In uranium-lead dating, the concordia diagram is used which also decreases the problem of nuclide loss.The only exceptions are nuclides that decay by the process of electron capture, such as beryllium-7, strontium-85, and zirconium-89, whose decay rate may be affected by local electron density.For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time.
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For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant.