How is the stability of a nucleus determined?

The stability of a nucleus is determined by the balance between the forces of repulsion and attraction within it.

The nucleus of an atom is composed of protons and neutrons, collectively known as nucleons. The stability of a nucleus is determined by the balance between two fundamental forces: the strong nuclear force, which binds the nucleons together, and the electromagnetic force, which causes the protons to repel each other due to their positive charge.

The strong nuclear force is much stronger than the electromagnetic force, but it only acts over very short distances. This means that in small nuclei, where all the nucleons are close together, the strong nuclear force dominates and the nucleus is stable. However, as the nucleus gets larger, the protons start to get further apart and the electromagnetic force becomes more significant. This can cause the nucleus to become unstable.

The ratio of neutrons to protons also plays a crucial role in the stability of a nucleus. For smaller elements (with atomic numbers up to about 20), the most stable nuclei have roughly equal numbers of protons and neutrons. For larger elements, however, more neutrons are needed to counteract the increased electromagnetic repulsion between the protons. If the neutron to proton ratio is too high or too low, the nucleus can become unstable.

Unstable nuclei can undergo radioactive decay, in which they emit particles and/or energy in order to become more stable. This can involve the emission of alpha particles (helium nuclei), beta particles (electrons or positrons), or gamma rays (high-energy photons), depending on the nature of the instability.

In summary, the stability of a nucleus is determined by the balance between the strong nuclear force and the electromagnetic force, as well as the ratio of neutrons to protons. If these factors are not in balance, the nucleus can become unstable and undergo radioactive decay.