Neutrons and Their Discovery

Chadwick’s Discovery of Neutron (1932)

James Chadwick discovered the neutron, a neutral subatomic particle, while studying atomic nuclei.

Experiment Setup:

• Chadwick bombarded beryllium (Be) foil with alpha particles ($\alpha$-particles from polonium).

• A mysterious radiation was emitted from beryllium.

• The radiation was directed onto paraffin wax, causing protons to be ejected.

Observations:

• The emitted radiation was not deflected by electric or magnetic fields, indicating it had no charge.

• The radiation could knock out protons from paraffin, suggesting it had mass similar to protons.

Conclusion:

• The radiation consisted of neutral particles, later named neutrons.

• Mass of neutron ≈ Mass of proton (1.675 × 10⁻²⁷ kg).

Diagram: Experiment Leading to Discovery of Neutrons

(A labeled diagram showing alpha particles hitting beryllium, emitting neutrons, and striking paraffin to eject protons.)

Chadwick’s discovery was crucial in understanding nuclear reactions, isotopes, and atomic bombs.