Potassium dating

Quite remarkable also is the very long half-life of 1;251 billion years, exceptional for a beta decay.

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.

In both argon 40 and calcium 40, however, the number of protons and neutrons are even, granting them that extra stability.

Along with uranium and thorium, potassium contributes to the natural radioactivity of rocks and hence to the Earth heat.

This isotope makes up one ten thousandth of the potassium found naturally.

At that moment, the rock contains a certain amount of potassium but no argon.

With time and the potassium 40 disintegrations, the gaseous argon atoms accumulate very slowly in the lava where they are trapped.

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.

Potassium 40 contains odd numbers of both – 19 protons and 21 neutrons.

As a result it has one bachelor proton and one bachelor neutron.

The beta electrons of the decay into calcium 40 (89.3% of the time) are not accompanied by gamma rays, and are generally absorbed into the medium they find themselves in.

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.

How can potassium 40 simultaneously have too many of both?