Draw a plot of BE/A versus mass number A for `2 le A le 170`. Use this graph to explain the release of energy in the process of nuclear fusion of two light nuclei.
OR
Using the curve for the binding energy per nucleon as a function of mass number A, state clearly how the release in energy in the processes of nuclear fission and nuclear fusion can be explained.
OR
Draw a plot of the binding energy per nucleon as a function of mass number for a large number of nuclei, `2 lt A lt 240`. How do you explain the constancy of binding energy per nucleon in the range `30 lt A lt 170` using the property that nuclear force is short-ranged ?

Explanation

The above curve shows that
(i) When a heavy nucleus breaks into two medium sized nuclei (in nuclear fission) the BF/nucleon increases resulting in the release of energy.
(ii) When two small nuclei combine to form a relatively bigger nucleus in nuclear fusion BF/nucleon increases, resulting in the release of energy.
OR
The constancy of the binding energy in the range `30 lt A lt 170` is a consequence of the fact that the nuclear force is short-ranged. If a nucleon can have a maximum of `p` neighbours within the range of nuclear force, its binding energy would be proportional top. If we increase A by adding nucleons they will not change the binding energy of a nucleon inside. Since most of the nucleons in a large nucleus reside inside it and not on the surface, the change in binding energy per nucleon would be small. Hence the binding energy per nucleon is a constant, (saturation property of nuclear forced.)