What is the force that involved in the interactions that allow nuclei to decay?

The electromagnetic force, which causes positively charged protons to repel one another, and the strong nuclear force, which binds protons and neutrons together to form the nucleus, must be in balance for nuclei heavier than hydrogen.

A nucleus that is unstable due to an excess of protons or neutrons can be balanced by beta decay, which is the process by which a proton becomes a neutron, a positron, and an electron neutrino, or a neutron becomes a proton, an electron, and an electron antineutrino.

Fusion reactions involving elements lighter than iron release energy in the form of heavier elements, whereas fusion reactions involving elements heavier than iron require additional energy.

Alpha particles are produced by unstable heavy nuclei; an alpha particle is a very stable helium-4 nucleus that forms when two protons and two neutrons bind together to form a helium nucleus inside the heavy nucleus. Occasionally, an alpha particle can escape through a quantum tunneling mechanism.

The weak nuclear force is the force that participates in the interactions that permit nuclei to decay.