The rules are the same in all cases; the assumptions are different for each method.To explain those rules, I'll need to talk about some basic atomic physics. Hydrogen-1's nucleus consists of only a single proton.Uraniums abbreviation is U, so uranium-238 can be more briefly written as U238.
For example, hydrogen-1 and hydrogen-2 are both nuclides of the element hydrogen, but hydrogen-1's nucleus contains only a proton, while hydrogen-2's nucleus contains a proton and a neutron.
Uranium-238 contains 92 protons and 146 neutrons, while uranium-235 contains 92 protons and 143 neutrons.
To keep it short, a nuclide is usually written using the elements abbreviation.
I found several good sources, but none that seemed both complete enough to stand alone and simple enough for a What is radiometric dating?
Simply stated, radiometric dating is a way of determining the age of a sample of material using the decay rates of radio-active nuclides to provide a 'clock.' It relies on three basic rules, plus a couple of critical assumptions.
Young-Earth creationists -- that is, creationists who believe that Earth is no more than 10,000 years old -- are fond of attacking radiometric dating methods as being full of inaccuracies and riddled with sources of error.When I first became interested in the creation-evolution debate, in late 1994, I looked around for sources that clearly and simply explained what radiometric dating is and why young-Earth creationists are driven to discredit it.Protons and neutrons together are called nucleons, meaning particles that can appear in the atomic nucleus.A nuclide of an element, also called an isotope of an element, is an atom of that element that has a specific number of nucleons.Radiometric dating methods are the strongest direct evidence that geologists have for the age of the Earth.All these methods point to Earth being very, very old -- several billions of years old.