The atomic nucleus offers a unique opportunity to study the competition between three of the four fundamental forces known to exist in nature, the strong nuclear interaction, the electromagnetic interaction and the weak nuclear interaction. Only the much weaker gravitational force is irrelevant for the description of nuclear properties. Although in general the decay of an excited nuclear state follows the hierarchy of these forces, there are sometimes exceptions.

Source: In a neutron-rich tin nucleus, electromagnetism can win over the strong force