Question

Mainly on which factor does the stability of a nucleus depend?

Hint:

Think about the balance between proton-proton Coulomb repulsion and the neutrons that supply extra nuclear binding.

Answer 1

Step 1: What holds a nucleus together. A nucleus contains protons and neutrons (nucleons). Protons repel one another electrostatically, while the short-range attractive nuclear force acts between all nucleons. Stability results from the balance of these forces, and neutrons contribute the extra nuclear attraction that offsets proton repulsion without adding charge.

Step 2: The deciding factor. Whether this balance favours stability depends mainly on the ratio of the number of neutrons to the number of protons, i.e. the neutron-to-proton ratio \(\dfrac{N}{Z}\).

Step 3: State the answer. The stability of a nucleus depends mainly on its neutron/proton ratio \((N/Z)\). For light nuclei stability corresponds to \(N/Z \approx 1\); for heavier nuclei the stable ratio rises to about \(1.5\) because extra neutrons are needed to dilute the growing proton repulsion.
\[\boxed{\text{Stability depends mainly on the neutron-to-proton ratio } N/Z.}\]