Concept Explanation: Gold Foil Scattering Experiment

The gold foil scattering experiment, conducted by Ernest Rutherford in 1911, was crucial in discovering the atomic nucleus. It involved firing a beam of radiation at a thin gold foil and observing the scattering pattern.

Step 1: Understanding the Experiment Requirements

To probe the atomic structure, the radiation needed to:

• Be massive enough to be deflected by atomic constituents
• Have high energy to penetrate the atom
• Be positively charged to interact with the positive nucleus

Step 2: Evaluating the Options

Gamma rays: Electromagnetic radiation with no mass or charge - cannot be deflected

Infrared rays: Low-energy electromagnetic radiation - insufficient energy and no charge

Beta particles: High-energy electrons with negative charge - would be attracted to positive nucleus but too light for significant deflection

Alpha particles: Helium nuclei with mass number 4 and charge +2 - massive and positively charged, perfect for nuclear scattering

Step 3: Why Alpha Particles Were Used

Alpha particles have sufficient mass (approximately 4 u) and positive charge ($2e^{+}$) to be repelled by the positive nucleus, allowing observation of large-angle scattering that revealed the nuclear model.

Final Answer

Alpha particle

Related Topics

• Atomic Structure and Models
• Rutherford's Nuclear Model
• Particle Scattering Theory
• Radioactive Decay and Radiation Types

Key Formulae and Theory

Rutherford Scattering Formula:

Alpha Particle Properties:

• Symbol: $\mathrm{He}_2{}_4{}^{\mathrm{2+}}$
• Mass: ~6.64 × 10^-27 kg
• Charge: +2e (3.2 × 10^-19 C)

Experimental Significance: The unexpected large-angle scattering of alpha particles led to the conclusion that atoms have a small, dense, positively charged nucleus, contradicting the plum pudding model.