5. Discovery of Neutrons (By J. Chadwick)

Who discovered the neutron and when?

James Chadwick, in 1932.

What problem did the neutron's discovery solve?

Explained atomic mass discrepancy and nucleus stability.

What was known about atomic structure before the neutron's discovery?

Atoms had protons (positive) and electrons (negative), but extra mass was unaccounted for.

What mysterious radiation was discovered in 1930, and by whom?

Bothe and Becker found radiation from beryllium bombarded with alpha particles, believed to be gamma rays.

How did Chadwick's experiment challenge the gamma-ray theory?

He hypothesized that neutral particles, not gamma rays, were causing protons to eject from paraffin wax.

What was the key finding from Chadwick’s experiments?

He found that neutral particles (neutrons) knocked protons out of substances, confirming their existence.

What are the properties of neutrons?

• Charge: Neutral

• Mass: Slightly more than a proton (1.675 × 10⁻²⁷ kg)

• Location: In the atomic nucleus

What role do neutrons play in the nucleus?

Neutrons stabilize the nucleus by counteracting proton-proton repulsion through the strong nuclear force.

How did neutrons impact atomic models?

They explained isotopes and the additional mass in the nucleus.

Why are neutrons crucial for nuclear chain reactions?

Their neutral charge allows them to penetrate atomic nuclei easily, making them ideal for starting nuclear reactions.

What are some major impacts of neutron discovery?

• Enabled nuclear fission (atomic bombs, nuclear energy)

• Explained isotopes

• Advanced nuclear physics

What award did Chadwick receive for his discovery?

Nobel Prize in Physics, 1935.