This atom is not stable, and will break down, releasing nuclear energy in the process.
Radioactive carbon (Carbon 14) is formed in the upper atmosphere as a byproduct of cosmic radiation.
It uses accelerator mass spectrometry to determine the amounts of C14 and C12 in a small sample which is vaporised in the test.
The ions produced are forced into a magnetic field where the different mass of the carbon isotopes causes a different deflection, allowing the quantity of each isotope to be measured.
The tiny initial amount of C14, the relatively rapid rate of decay (the half-life of C14 is currently about 5700 years) and the ease with which samples can become contaminated make radiocarbon dating results for samples "older" than about 50,000 years effectively meaningless.
This limit is currently accepted by nearly all radiocarbon dating practitioners.
But measuring how much carbon-12 is in a formerly living thing compared to carbon-14 and doing some math with what is called a half-life you can date things to within a certain range.
Unfortunately it is not precise enough to date some really old things with much certainty, and it can only be used to date stuff that was once alive.
This collision is less destructive than the initial collision that produced them.
Usually a proton is knocked out of the nitrogen atom's nucleus and is replaced with the neutron.
Every 5,730 years, approximately half of this radioactive carbon spontaneously converts itself back into nitrogen by emitting an electron from a neutron.