Question 15: Why are heavy nuclei unstable?
In the nucleus, nucleons (both protons and neutrons) are under the influence of two forces; (1) Coulomb’s force of repulsion among the protons (2) Strong nuclear force of attraction among the nucleons.
Now the strong nuclear force is a small range force, effective in extremely small distances and Coulomb’s repulsion force exists to a relatively long distances.
The large nuclei have larger sizes; therefore, large distances between the nucleons on the peripheries (sides). The strong nuclear force of attraction is less effective among these nucleons as compared to the Coulomb’s force of repulsion among the protons. Therefore, this makes the large nuclei less stable.