Some heavy nuclei, containing even more protons than the uranium nucleus undergo “spontaneous fission,” splitting apart without absorbing a neutron. Why is spontaneous fission observed only in the heaviest nuclei?
Solution 3E The electric attraction between protons is weaker than the repulsive nuclear force in the heaviest nuclei. In the heavy atom, the outermost electrons are very far from the centre of the atom. The gravitational forces are small for light nuclei. A light nucleus does not have enough energy for fission. Explanation: The electric repulsion between protons reaches across the whole nucleus, affecting all protons, Whereas, the attractive nuclear force reaches only from one nucleon to its immediate neighbors. So, the more protons in a nucleus, the more likely it is that their mutual repulsion will overcome the attractive forces and lead to spontaneous fission.