What is the natural transmutation which forms most of the argon in air?

1 Answer
Oct 17, 2015


Potassium-40 decays to argon-40 via electron capture.


Potassium-40, #""^40"K"#, will decay to argon-40, #""^40"Ar"#, via electron capture.

Electron capture takes place when an electron from the inner shells of an atom is captured by the nucleus. The negatively charged electron will combine with a proton, which is a positively charged particle, to form a neutron.


In addition to this, an electron neutrino, #nu_e#, is being emitted.

So, if a proton is being converted to a neutron, it follows that the identity of the atom will change. More specifically, its atomic number will decrease by #1#.

Its mass number, which tells you the total number of protons and neutrons in the nucleus, will remain unchanged.

The nuclear equation for the electron capture decay of potassium-40 to argon-40 looks like this

#""_19^40"K" + ""_text(-1)^0"e"^(-) -> ""_18^40"Ar" + nu_e#

About one in nine potassium-40 atoms decays to argon-40, the rest decay to calcium-40 via beta minus decay.