Question

why is it said that nuclear forces are saturated forces.​

Answer 1

Suppose a nucleus consists of Z protons and N neutrons, which coalesce together to form the nucleus of mass M(Z, N). The mass M(Z, N) of the nucleus, is less than the sum of the masses of Z protons ( Z×Mp) and N neutrons (N×Mn).

The difference between these masses is the binding energy of the nucleus, i.e.

B.E. = M(Z, N) - { Z×Mp + N×Mn}

This total binding energy is of Z +N =A nucleons in the nucleus.

The binding energy per nucleon is (B. E./ A).

This binding energy per nucleon is found to be fairly constant over the whole range of the periodic table.

Now if every nucleon in the nucleus could interact with every other nucleon in the nucleus, there would be A× (A - 1 ) interacting pairs, i.e the total binding energy would be proportional to A² , i. e. the binding energy per nucleon would have been proportional to A, rather than being independent of A.This happens because the nuclear force is a short range and falls off very rapidly beyond a critical value, and nucleons interact only with their first neighbours and not beyond that i.e. their strength becomes saturated over a short distance.

Answer 2

Suppose a nucleus consists of Z protons and N neutrons, which coalesce together to form the nucleus of mass M(Z, N). The mass M(Z, N) of the nucleus, is less than the sum of the masses of Z protons ( Z×Mp) and N neutrons (N×Mn).

The difference between these masses is the binding energy of the nucleus, i.e.

B.E. = M(Z, N) - { Z×Mp + N×Mn}

This total binding energy is of Z +N =A nucleons in the nucleus.

The binding energy per nucleon is (B. E./ A).

This binding energy per nucleon is found to be fairly constant over the whole range of the periodic table.

Now if every nucleon in the nucleus could interact with every other nucleon in the nucleus, there would be A× (A - 1 ) interacting pairs, i.e the total binding energy would be proportional to A² , i. e. the binding energy per nucleon would have been proportional to A, rather than being independent of A.This happens because the nuclear force is a short range and falls off very rapidly beyond a critical value, and nucleons interact only with their first neighbours and not beyond that i.e. their strength becomes saturated over a short distance.