Question

Why can heavy nuclei with odd numbers of neutrons be induced to fission with thermal neutrons, whereas those with even numbers of neutrons require more energy input to induce fission?

a) Odd-neutron nuclei are more stable
b) Even-neutron nuclei are more stable
c) Odd-neutron nuclei have higher binding energy
d) Even-neutron nuclei have higher binding energy

Answer 1

Heavy nuclei with odd numbers of neutrons can be induced to fission with thermal neutrons due to the additional energy deposited in the resulting nucleus. Heavy nuclei with even numbers of neutrons require more energy input as they are already more stable.

Step-by-step explanation:

Heavy nuclei with odd numbers of neutrons can be induced to fission with thermal neutrons because the nuclear force is more attractive for an even number of neutrons. When a neutron encounters a nucleus with an odd number of neutrons, the additional neutron makes the number even, resulting in about 2-MeV more energy being deposited in the resulting nucleus.

This extra energy produces greater deformation, making fission more likely. On the other hand, heavy nuclei with even numbers of neutrons require more energy input to induce fission because they are already more stable due to the even number of neutrons.