Nuclei of nitrogen-14 can capture thermal neutrons to produce carbon-14 and a proton, but they do not undergo fission or emit further neutrons.
In contrast, when plutonium-239 nuclei absorb neutrons, they undergo induced fission and release multiple neutrons per fission event.
Explain why a self-sustaining chain reaction can occur in a sample of plutonium-239 but not in a sample of nitrogen-14.