Can you write the nuclear equation for the decay of potassium-42?

1 Answer
Aug 12, 2018

Potassium undergoes beta (minus) decay to produce an electron and a calcium nucleus.

4219K4220Ca+e

Explanation:

Naturally-occurring potassium atoms have a weighted average atomic mass of 39.10 (as seen on most modern versions of the periodic table.) Each potassium atom contains 19 protons p+ and thus an average potassium atom contains about 39.101920 neutrons n0.

This particular isotope of potassium-42 contains 42 nucleons (i.e., protons and neutrons, combined;) Like other isotopes of potassium 19 out of these nucleons are protons; the rest 4219=23 are therefore neutrons.

Only a certain range of neutron-to-proton ratios are capable of producing stable isotope. Light nuclei that are unstable would undergo beta decay spontaneously to convert one or more of its protons to neutrons or vice versa. The decay favors the process that leads to the most stable configuration. A potassium-42 nucleus contains more neutrons than necessary and would seek to convert at least one of its neutrons to protons. It would thus undergo beta-minus decay as one of its neutrons converts to a proton, releasing an electron:

10n11p+e
4219K4220Ca+e

The following image from Wikimedia Commons summarizes decay modes common isotopes demonstrates. 4219K lies in the blue area above the black line (resembling stable nuclei;) isotopes in this field tend to undergo beta-minus decay, releasing an electron.

By Table_isotopes.svg: Napy1kenobiderivative work: Sjlegg (talk) - Table_isotopes.svg, CC BY-SA 3.0 By Table_isotopes.svg: Napy1kenobiderivative work: Sjlegg (talk) - Table_isotopes.svg, CC BY-SA 3.0

[1] https://commons.wikimedia.org/w/index.php?curid=6703703