Rutherford's Alpha-Particle Scattering Reveals Nuclear Structure

Steps:

• Recall the experiment: Alpha particles fired at thin gold foil, most pass through but some deflect sharply.
• Analyze results: Large-angle deflections indicate a tiny, dense, positively charged nucleus repelling alphas via Coulomb's law.
• Connect to choices: Deflections quantify nuclear radius (about 10^-15 m) from scattering angles and impact parameters.
• Eliminate others: No evidence for fusion, decay, or isotopes in scattering patterns.

Why D is correct:

• Scattering follows Rutherford's formula, σ(θ) ∝ (Z1 Z2 e² / (4πε₀ E))² cot²(θ/2), where close approaches reveal the nucleus's small size by allowing most particles to pass undeflected.

Why the others are wrong:

• A: No fusion observed; experiment probed existing atomic structure, not merging nuclei.
• B: No decay products detected; focused on elastic scattering, not spontaneous emission.
• C: Isotopes differ in neutron number, but experiment measured charge (Z), not mass variants.

Final answer: D