Potassium 40 argon 40 dating
The others decay to Ca-40, which is the only natural isotope of calcium.
It can only escape when the rock is in its molten state, and so the amount of fossilized argon present in lava allows scientists to date the age of the solidification.Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. 1979, 1986 © Harper Collins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Cite This Source potassium-argon dating A method of radiometric dating, involving analysis of the ratio of potassium 40 (a radioactive isotope of potassium) to argon (the product of radioactive decay of potassium 40) in a given sample.This is perhaps the closest approach to an ideal dating system. Furthermore, since argon is an inert gas and doesn't combine naturally with other elements, it has no business being in a crystal lattice at all.This is explained by a large jump in the internal rotation (or spin ) of the nucleus during the decay, which almost forbids the transition particularly difficult, therefore making it extremely slow.IN2P3Potassium 40 has the unusual property of decaying into two different nuclei: in 89% of cases beta-negative decay will lead to calcium 40, while 11% of the time argon 40 will be formed by electron capture followed by gamma emission at an energy of 1.46 Me V.It can only be there if it formed by radioactive decay.
Well, there are a few complications: Potassium 40 has a branched decay: only 1/9 of all K-40 atoms decay to Ar-40.
With a half-life of 1,251 billion years, potassium 40 existed in the remnants of dead stars whose agglomeration has led to the Solar System with its planets.
The two decay channels of potassium 40The decay scheme of potassium-40 is unusual.
The mass energy of atom is above these of its two neighbours in the family of atoms with 40 nucleons in their nucleus : Argon-40 with one proton less and calcium-40 with one proton more. The beta-minus decay channel leading to calcium_40 is by far the most frequent, but decays leading to argon-40 by electronic capture occurs at a rate of 11 %.
Quite remarkable also is the very long half-life of 1;251 billion years, exceptional for a beta decay.
The cure for this problem is pretty straightforward.