Atomic Structure, Radioactivity, and Nuclear Reactions: Lessons 4–5

Radioactivity

Process by which unstable nuclei emit radiation.

Radiation

Energy or particles emitted from a radioactive source.

Radioisotopes

Isotopes with unstable nuclei (too many/few neutrons).

Radioactive Decay

Spontaneous breakdown of unstable nuclei → smaller elements + radiation.

Nuclide

An isotope identified by its proton + neutron count.

Transuranium Elements

Elements with Z≥92; unstable, synthetic, decay rapidly.

Stable nuclei

Do NOT spontaneously decay.

Atomic numbers 1-20 stability

Stable if p+:n0=1:1.

Example of Carbon-12

6 protons, 6 neutrons.

Atomic numbers 21-83 stability

Stable if p+:n0=2:3.

Example of Mercury-200

80 protons, 120 neutrons.

Atomic numbers ≥ 84

No stable isotopes; all radioactive.

Transmutation

Conversion of one element into another.

Decay chains

Series of decays (α, β, γ) leading to stability.

Parent nuclide

Original unstable nucleus.

Daughter nuclides

Products formed until stability is reached.

Alpha decay

Mass ↓4, Atomic # ↓2.

Beta-minus decay

Neutron → Proton + electron. Mass unchanged, Atomic # +1.

Beta-plus decay

Proton → Neutron + positron. Mass unchanged, Atomic # -1.

Gamma decay

Energy only, no mass change.

Alpha radiation

Heaviest, most damaging locally, blocked by paper.

Beta radiation

Lighter, medium penetration, blocked by foil/glass.

Gamma radiation

Pure energy, deepest penetration (stopped by lead/concrete).

Nuclear Fission

Splitting of a large nucleus (U, Pu) after neutron bombardment.

Fission products

Produces 2 smaller nuclei, 2-3 neutrons, and huge energy.

Chain reactions

Released neutrons trigger more fission.

Controlled fission

Used in nuclear reactors.

Uncontrolled fission

Used in nuclear weapons (with enriched U-235 or Pu-239).

Nuclear Fusion

Combining small nuclei (like hydrogen isotopes) into one larger nucleus.

Fusion energy release

Releases 3-10x more energy than fission.

Example of Fusion

1H + 3H → 4He + 0n + energy.