Plot of binding energy per nucleon is shown in Figu.re. From B-E/nucleon curve, we note that first B.E. increases rapidly and decreases slowly and B.E Is max i.e. 8.8 Mev for 56Fe atom. Again by decreasing slowly B.E. becomes 8.5 Mev .for uranium atom 23892U This shows that nucleus with mass number A < 20 are less stable, but some nucleus as 4He,12C,16O (even-even) nuclei are stable. Thus the nuclei with mass number A ≤ 20 shows fusion reaction as 2H and 3H have very low B-E/nucleon in comparison to 4He. Thus when two very light nuclei (A ≤ 10 say) fuse to form a heavy nucleus, the B.E/A of the fused heavier nucleus is more than the B.E/A of lighter nuclei. This implies the release of energy in nuclear fusion. Similarly, due to fission of a very heavy nucleus the B.E/A of the product as daughter nuclei increases which implies the release of huge amount of energy. Thus for lighter nuclei nuclear fusion and for heavier nuclei, nuclear fission takes place and huge amount of energy is released.
