I love gold. Do you love gold? I think everyone loves gold!
It is common enough for everyone to have a little bit of it, but rare enough to hold its intrinsic value. Gold doesn’t tarnish, oxidize, or interact much with other elements at all; it is very stable. In fact, Gold is the heaviest known ‘monoisotopic’ element, meaning that 100% of all naturally occurring gold comes in just one form: the perfectly stable Au-197 isotope. That’s the main reason why I love gold!
Stable elements, such as Gold (Au-197), are those which have no tendency to "decay", i.e., change into another element.
Unstable elements, on the other hand, have isotopes that decay from one state to another – and this is the basis of radioactivity.
The dictionary definition of radioactivity is “The emission of ionizing radiation or particles caused by the spontaneous disintegration of unstable atomic nuclei.”
Ok, that’s quite a mouthful. But note that wording which says “spontaneous disintegration” of the atomic nuclei. Spontaneous disintegration happens instantly. At one point in time, there is an atom – and then suddenly you have a different atom (or a different isotope) and an emission of ionizing radiation (i.e., the “radio activity”).
The point in time for any disintegration is completely indeterminate. We can never know exactly when any individual atom will decay. However, we can absolutely say, from a statistical standpoint, how many atoms will decay in a specific time period, and that time period is called the “Half-Life” of the element.
The half-life is the time that it takes for half the atoms in any given sample to decay. It doesn’t matter if you have just a few hundred atoms, or trillions upon More...