Question

A pair of nuclei for which Z₁ = N₂ and Z₂ = N₁ are called mirror isobars. (The atomic and neutron numbers are interchangeable.) Binding-energy measurements on such pairs can be used to obtain evidence of the charge independence of nuclear forces. Charge independence means that the proton-proton, proton-neutron, and neutron-neutron forces are approximately equal. Calculate the difference in binding energy for the two mirror nuclei 7 3 Li and 7 4 Be.

Answer: _____ MeV

Answer 1

for 7/3 Li

E = [3 * 1.007825 + 4 * 1.008665 - 7.016005 ] * 931.494 = 39.2438

binding energy per nucleon = 109.1106/7 = 5.606

for 7/4 Be

E = (4 * 1.007825 + 3 *1.008665 - 7.0171) *931.494 = 37.4414

binding energy per nucleon = 5.349

difference in binding energy = 5.349 - 5.606 = 0.257 MeV

The isobars with more protons experience more Coulomb repulsion and consequently are

less tightly bound than those with less protons