What determines the stability of a nucleus?

The stability of a nucleus is determined by the balance between the strong nuclear force and the electromagnetic force.

The nucleus of an atom is composed of protons and neutrons, collectively known as nucleons. The stability of this nucleus is primarily determined by two fundamental forces: the strong nuclear force and the electromagnetic force. The strong nuclear force, as the name suggests, is the strongest of the four fundamental forces of nature. It acts to bind protons and neutrons together in the nucleus. However, it has a very short range, acting only over distances comparable to the size of the nucleus.

On the other hand, the electromagnetic force, which causes like charges to repel each other, acts between the protons in the nucleus. This force has a much longer range than the strong nuclear force and acts to push the protons apart. The balance between these two forces determines the stability of the nucleus. If the strong nuclear force is greater than the electromagnetic force, the nucleus is stable. If the electromagnetic force is greater, the nucleus is unstable and may undergo radioactive decay.

The number of protons and neutrons in the nucleus also plays a crucial role in its stability. Nuclei with a certain number of nucleons, known as 'magic numbers', have extra stability. These magic numbers are 2, 8, 20, 28, 50, 82, and 126. Nuclei with these numbers of protons or neutrons are more stable than those with other numbers. This is due to the shell structure of the nucleus, similar to the shell structure of electrons in an atom.

Furthermore, the ratio of neutrons to protons is also important. For lighter elements, a 1:1 ratio of neutrons to protons makes the nucleus stable. However, for heavier elements, more neutrons are needed to counterbalance the increased electromagnetic repulsion between the larger number of protons.

In summary, the stability of a nucleus is determined by the balance between the strong nuclear force and the electromagnetic force, the number of protons and neutrons, and the ratio of neutrons to protons.