Question

Why does the bonding energy per nucleon decrease with A for higher values of A (or increase with A for lower values)?

A. Because pion exchange opportunities decrease with A.
B. Because gluons get weaker with A.
C. Because Z increases with A.
D. Because volume decreases with A.

Answer 1

As mass number increases, the binding energy/nucleon decreases gradually. This is due to Colombian repulsion between the protons and therefore heavy nuclei are relatively less stable.

The decrease in the binding energy/nucleon at high mass numbers tells us that nucleons are more lightly bound when they are assembled into two middle mass nuclei than in a single high mass nucleus. Therefore, energy can be released in nuclear fission of a single massive nucleus into smaller fragments.