In fission, the released neutrons and energy come from what phenomenon?

• A. Mass defect converting to energy (approx 200 MeV) per fission.
• B. Energy from electron rearrangement only.
• C. Energy from proton acceleration only.
• D. No energy release in standard fission.

Answer: (A)

In fission, the energy and the neutrons come mainly from the mass defect: the total rest mass of the fission fragments and emitted neutrons is less than the mass of the original heavy nucleus. That difference is converted into energy via E = mc^2. The heavy nucleus splits into lighter fragments that are more tightly bound to their nucleons, so the overall mass decreases and that lost mass reappears as energy. Roughly 200 MeV are released per fission, with most of that energy appearing as the kinetic energy of the fission fragments, some as the energy of prompt neutrons, and a portion as gamma radiation. Energy from atomic electron rearrangement or from proton acceleration would be far smaller and does not account for the large nuclear energy release. There is indeed energy release in standard fission.