Which process releases energy by splitting a heavy nucleus into smaller parts?

• A. Fusion
• B. Fission
• C. Spontaneous decay
• D. Neutron emission

Answer: (B)

Energy release from splitting a heavy nucleus into lighter fragments comes from the fact that the resulting nuclei have a higher binding energy per nucleon than the original heavy nucleus. The mass of the products is slightly less than the mass of the initial nucleus, and that difference appears as energy (mass defect converted to energy). In fission, a heavy nucleus such as uranium-235 captures a neutron, becomes highly unstable, and splits into two lighter nuclei plus several neutrons, releasing a large amount of energy (about 200 MeV per fission). The released energy is mostly the kinetic energy of the fragments, with some energy carried by the emitted neutrons and gamma radiation; those neutrons can trigger further fission in surrounding material, creating a chain reaction. By contrast, fusion releases energy by combining light nuclei into heavier ones, spontaneous decay is a different mode of radioactive transformation, and neutron emission involves simply ejecting a neutron without splitting the nucleus.