Potassium argon radioactive dating

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.This 1.46 Me V gamma ray is important, as it allows us to identify when potassium 40 decays.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.DR Potassium 40 is a radioisotope that can be found in trace amounts in natural potassium, is at the origin of more than half of the human body activity: undergoing between 4 and 5,000 decays every second for an 80kg man.Along with uranium and thorium, potassium contributes to the natural radioactivity of rocks and hence to the Earth heat.

IN2P3Stable nuclei sit at the bottom of a so-called ‘valley of stability’, a concept that helps determine whether a nucleus is radioactive or not.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 %.The decay of potassium into argon produces a gaseous atom which is trapped at the time of the crystallization of lava.The atom can escape when the lava is still liquid, but not after solidification.

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