Question

When is the nucleus said to be unstable

Answer 1

In unstable nuclei the strong nuclear forces do not generate enough binding energy to hold the nucleus together permanently. It is unstable nuclei that are radioactive and are referred to as radioactive nuclei and in the case of their isotopes called radioisotopes.

The unstable nuclei lie above and below the line of stability in the neutron – proton plot. This gives information of the type of radioactive decay they will undergo. Nuclei which lie above the line of stability contain too many neutrons to be stable. They are referred to as “neutron rich”. Those that lie below the line of stability contain too many protons to be stable and are called “proton rich”.

In summary it is the balance of protons and neutrons in a nucleus which determines whether a nucleus will be stable or unstable. Too many neutrons or protons upset this balance disrupting the binding energy from the strong nuclear forces making the nucleus unstable. An unstable nucleus tries to achieve a balanced state by given off a neutron or proton and this is done via radioactive decay

Answer 2

Answer:

An atom is unstable (radioactive) if these forces are unbalanced; if the nucleus has an excess of internal energy. Instability of an atom's nucleus may result from an excess of either neutrons or protons.

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