Argon argon dating technique
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.
Or if we consistently get one date for the steps below (for example) 400°C, and consistently get another date in the steps above 400°C, then it seems as though argon loss occurred as a result of metamorphism at a temperature of about 400°C, with the younger date representing the date of the metamorphism, and the older date representing the formation of the rock; and we can investigate this clue further by looking for other evidence of the metamorphic event.
And if the dates we get are all over the place, then we are probably looking at excess argon.
Common phases to be used for argon-argon dating are white micas, biotite, varieties of potassium feldspar (especially sanidine because it is potassium-rich), and varieties of amphibole. This can be used to solve equation 2 for the sample.
J is a factor which depends on the nature of the neutron bombardment.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.Now the bad news is that there is no way we can somehow manipulate this data to give us a correct date for the sample.But the good news is that we do know that there's a problem; whereas if we'd analyzed the same rock using the K-Ar method, then it would have supplied us with a date and there'd have been no sign in the K-Ar data of anything wrong with it.