Radiometric dating decay curves
Not all isotopes undergo decay: those that do are called unstable isotopes (or radioactive isotopes) and conversely those that don't are called stable. As we can see from this example, it is perfectly possible for different isotopes of the same element to differ in their stability.The reader should note that when a parent atom decays to a daughter atom, the daughter is not necessarily stable; sometimes the daughter will undergo further decay. It is important to understand how and why radioactive decay takes place.Consider what this means if we have a large sample of Na has a 50% chance of decaying; or, equivalently the time over which our statistical expectation is that 50% of the sample will have decayed.Such situations are mathematically well-understood, and can be represented by the equation for exponential decay: Pd for 6.5 million years to check that this is how long it takes for half of it to decay? After all, by analogy, it is not necessary for a police officer to observe your car for an hour to report that you were traveling at 72 kilometers per hour.As a prelude to the articles on radiometric dating, it is desirable that the reader should know something about the mechanisms of radioactive decay.This article provides a fairly non-technical explanation of what it is and how it works.Because the energy emitted from the nucleus when it decays is so very small, it is possible to change its half-life by ionizing it.
Those isotopes which are produced by radioactive decay are said to be radiogenic.
It is obvious from this example that the exactness of our knowledge of the half-life will depend on the exactness with which we can measure the initial size of the sample and the rate at which it decays.
Each unstable isotope, then, has its own characteristic half-life.
However, two atoms can have the same atomic number and different atomic weights.
So, for example, C (carbon-14) has six protons and eight neutrons.
Search for radiometric dating decay curves:
An atom with six protons and eight neutrons is written as C.