Argon isotope dating
A precise amount of argon-38 is added to the gas as a "spike" to help calibrate the measurement, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen.
Then the gas sample is cleaned of all unwanted gasses such as H A variant of the K-Ar method gives better data by making the overall measurement process simpler.
Potassium (K) is one of the most abundant elements in the Earth's crust (2.4% by mass).
For every 100 K-40 atoms that decay, 11 become Ar-40.The key is to put the mineral sample in a neutron beam, which converts potassium-39 into argon-39.