Why do atomic nuclei deacay?

Answer 1

The strongest force we know of in nature is called the strong attraction, or strong nuclear force. It binds together atoms, but at the level of the ordinary human observer, it cannot be seen because it only operates at an atomic level.

Another, far weaker, force, which is also unseen at the human level, is the weak interaction, or weak nuclear force. It makes nucleons (protons and neutrons) want to come apart.

When nucleons are assembled in a nucleus, one might say the weak force can accumulate more than the strong force, depending on how the numbers of protons and neutrons come down. This, by itself, does not cause an atom to come apart, because if it could do that, the atom would not come together to begin with. But it can make an atom very unstable.

What the atom needs to decay is two things, this instability, and some unpredictable event. The actual event can any of a variety of things, but two can provide examples. The first is that something very energetic smashes into the nucleus of the atom; since the atom is already unstable, it might fly apart. Another is what is called vacuum fluctuation, which can be seen as a tiny disturbance in space; it can increase the instability to the point that the atom decays spontaneously.

There are any number of things that usually do not contribute to radioactive decay, and these include heat, chemical bonding (or the lack thereof), and pressure, along with a long list of other things.