What is the difference between nuclear fission and fusion?

Nuclear fission: A heavy nucleus (like U-235) splits into two medium-sized nuclei, releasing ~200 MeV per fission. Used in nuclear power plants and bombs. Produces radioactive waste. Nuclear fusion: Two light nuclei (like H-2 and H-3) combine to form a heavier nucleus, releasing ~17.6 MeV per fusion. Powers the Sun. Requires ~10 million°C. Much cleaner (less radioactive waste). Fusion releases more energy per unit mass but is harder to achieve on Earth.

Why is binding energy per nucleon maximum for iron-56?

Binding energy per nucleon (BE/A) represents nuclear stability. For very light nuclei (H, He), nuclear forces are weak and few — low stability. For very heavy nuclei (U, Th), electrostatic repulsion between many protons weakens the binding — lower BE/A. Iron-56 has the optimal balance of nuclear attractive force and minimal electrostatic repulsion, giving it the highest BE/A (~8.8 MeV). Any reaction moving nuclei toward iron releases energy.

Radioactivity, Nuclear Decay, and Nuclear Reactions

Atoms and Nuclei • Class 12 Physics • NCERT • CBSE

Radioactive decay law: N = N₀e^(−λt). Half-life T½ = 0.693/λ. Activity A = λN. Mass defect: Δm = (Zmp + Nmn) − M. Binding energy BE = Δm × 931.5 MeV.

Key Formulas

N = N₀ e^(−λt)
T½ = 0.693/λ
Activity A = λN
BE = Δm × 931.5 MeV
R = R₀A^(1/3), R₀ = 1.2 fm

Frequently Asked Questions

What is the difference between nuclear fission and fusion?: Nuclear fission: A heavy nucleus (like U-235) splits into two medium-sized nuclei, releasing ~200 MeV per fission. Used in nuclear power plants and bombs. Produces radioactive waste. Nuclear fusion: Two light nuclei (like H-2 and H-3) combine to form a heavier nucleus, releasing ~17.6 MeV per fusion. Powers the Sun. Requires ~10 million°C. Much cleaner (less radioactive waste). Fusion releases more energy per unit mass but is harder to achieve on Earth.
Why is binding energy per nucleon maximum for iron-56?: Binding energy per nucleon (BE/A) represents nuclear stability. For very light nuclei (H, He), nuclear forces are weak and few — low stability. For very heavy nuclei (U, Th), electrostatic repulsion between many protons weakens the binding — lower BE/A. Iron-56 has the optimal balance of nuclear attractive force and minimal electrostatic repulsion, giving it the highest BE/A (~8.8 MeV). Any reaction moving nuclei toward iron releases energy.

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