Mass–energy check in fission: compared with the original heavy nucleus, the sum of the rest masses of the two fission product nuclei is

Introduction / Context:Nuclear fission converts a small amount of mass into a large amount of energy, manifested primarily as kinetic energy of fission fragments plus neutron and gamma energies. Understanding the mass balance qualitatively is central to reactor physics.

Given Data / Assumptions:

• Heavy nucleus such as U-235 absorbs a neutron and splits.
• Two fission product nuclei and several neutrons are produced.
• Binding energy considerations determine the mass defect.

Concept / Approach:The mass of the products (two nuclei + emitted neutrons) is less than the mass of the original nucleus plus the captured neutron by an amount Δm. The corresponding energy release is E = Δm * c^2, about 200 MeV per fission. Thus, the sum of the two product nuclei alone is necessarily less than the original heavy nucleus mass.

Step-by-Step Solution:1) Write qualitative balance: m_initial > m_products_total.2) Attribute the difference to increased binding energy of medium-mass nuclei and released kinetic/gamma energy.3) Conclude “Less”.

Verification / Alternative check:Binding energy per nucleon peaks around iron; splitting heavier nuclei increases total binding energy, forcing a reduction in rest mass.

Why Other Options Are Wrong:“More” or “much more” would violate energy accounting for exoergic fission.“Same” would imply zero energy release.

Common Pitfalls:Ignoring the masses of emitted neutrons in casual statements; mixing up rest mass with relativistic kinetic energy of fragments.

Final Answer:Less