Question

Explain why, on the curve of binding energy, the average binding energy per nucleon of 4He2 is greater than that for 6Li3, a nuclide with a greater atomic mass than helium-4? (Give a written explanation. No calculations are required.)

Answer 1

alpha particle or  ^{4 ₂}He shows a sharp peak in binding energy curve and its binding energy is greater than that of 6Li3, although the mass of Li is greater. Binding energy is energy per nucleon, so looking at energy per nucleon rather than just the atomic mass.

The reason why 4He2 is abnormal on this curve is due to highly stable combination. To add more, alpha particle's charge decreses from center exponentiallly just as the Helium's electron cloud, in other words pair of protons and neutrons in alpha particle behave the same way as one helium pair of electron cloud. Hence, zero angular momentum, adding or removing one more neutron would require angular momentum and less release of energy, so this alpha particle with two neutrons and two protons is highly stable. Thats why its binding energy is great, as it is difficult to separate alpha particle into its constituents.