QUESTION:
Which one of the following concepts explains why heavy nuclei do not follow the N = Z line?
a) Pauli exclusion principle
b) transmutation
c) Coulomb’s repulsion
d) Heisenberg uncertainty principle
e) particle-wave duality
SOLUTION:
Answer: c)
The reasons for the heavy nuclei having more neutrons than the protons are mainly due to Coulomb’s repulsion. That is, it’s due to the balance between Coulomb force between protons and nuclear force due to nucleons.
Since protons repel each other so, the addition of new protons results in a larger repulsive Coulomb force. The Coulomb force must be balanced by the strong and short-range nuclear force.
Since, the nuclear force has a finite range so, to balance the Coulomb force in heavier nuclei, some extra neutrons are needed. And hence, the heavy nuclei do not follow the N=Z line.
Here, N indicates neutron number, and Z indicates the number of protons.