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

Oct 17, 2015

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

#### Explanation:

Potassium-40, $\text{^40"K}$, will decay to argon-40, $\text{^40"Ar}$, 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

$\text{_19^40"K" + ""_text(-1)^0"e"^(-) -> ""_18^40"Ar} + {\nu}_{e}$

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