Isotope dating wiki
Isotope dating wiki - colombian dating
Some of the problems of K-Ar dating can be avoided by the use of the related Ar-Ar dating method.In this article we shall explain how this method works and why it is superior to the K-Ar method.
In the previous article I introduced you to K is a stable isotope of potassium, which by definition means that it will not spontaneously undergo decay into another isotope.However, if you put it near the core of a nuclear reactor, so that it is bombarded by neutrons, then this will convert it into Ar.This isotope of argon is quite unstable, having a half-life of only 269 years.Consequently, the amount of it found in rocks is negligible — unless you subject them to an artificial neutron source.A crucial point to note is that because K are isotopes of the same element, they have the same chemical properties.So now we know J, and we have measured the R-value of the sample we're actually interested in dating, so we can use these data to solve the equation for t, giving us the age we're looking for.
You will note that this means that we have to be able to date some rocks accurately using some method other than Ar-Ar, so that we can find a standard to use for the determination of J; fortunately we can do this, and geologists have put a lot of effort into identifying rocks which can be accurately dated and used as standards.So far, all we seem to have done is taken the K-Ar dating method and made it much more complicated for no apparent reason.Therefore when the rock first forms, some of the minerals in it will have more potassium in and some less, but all the minerals will have the same initial ratio of But what is J?J is a factor which depends on the nature of the neutron bombardment.J is not calculated on theoretical grounds, but is found experimentally; alongside the sample we're interested in, we irradiate and then heat a sample of known age (a standard).Measuring the Ar emitted from the standard, and knowing the time t that it was formed, we can put these figures into the equation above and solve it for J.