This lesson covers radioactive decay, types of radiation, nuclear equations, half-life, and the uses and dangers of radioactivity.

1. Core Concepts (Short Notes)

22.1 Radioactivity

Radioactivity is the spontaneous disintegration of an unstable nucleus, releasing radiation.

• Unstable nuclei undergo decay to become stable.

• A nuclear process—not chemical.

22.2 Types of Radiation

There are three main types:

(a) Alpha (α) Particles

• Helium nuclei (⁴₂He)

• Charge: +2

• Low penetrating power (stopped by paper)

• Highly ionizing

(b) Beta (β) Particles

• High-speed electrons (⁰₋₁e)

• Charge: –1

• Medium penetration (stopped by aluminum)

• Moderate ionizing power

(c) Gamma (γ) Rays

• Electromagnetic radiation

• No charge, no mass

• Very high penetration (reduced by thick lead)

• Low ionizing but very dangerous

22.3 Nuclear Equations

Show changes in mass and atomic number:

Alpha decay: A → (A−4) Z → (Z−2)

Beta decay: A → A Z → (Z+1)

Gamma emissions accompany α or β decay (no change in A or Z).

22.4 Half-Life (t½)

Time taken for half the nuclei in a radioactive sample to decay.

• Constant for each isotope.

• Independent of temperature, pressure, or chemical state.

Formula: Remaining amount = Initial amount × (1/2)ⁿ Where n = number of half-lives.

22.5 Activity (A)

Rate of decay. A = λN Where:

• λ = decay constant

• N = number of nuclei

22.6 Detection of Radiation

• Geiger–Müller tube

• Cloud chamber

• Photographic plates

2. Applications of Radioactivity

22.7 Medical Uses

• Cancer treatment (Co-60)

• Imaging (technetium-99m)

22.8 Industrial Uses

• Thickness control

• Leak detection

• Radiography of metal parts

22.9 Agricultural Uses

• Food irradiation

• Pest control

22.10 Archaeological Dating

• Carbon-14 dating used to determine age of fossils and artifacts.

3. Dangers & Safety

22.11 Hazards

• Causes ionization in cells

• Can lead to mutations, cancer

• Damages tissues

22.12 Safety Measures

• Use shielding (lead)

• Maintain distance

• Limit exposure time

• Wear dosimeters

4. Tips & Tricks for Exams

• Alpha is the most ionizing but least penetrating.

• Beta increases atomic number by +1.

• Gamma causes no change in mass or atomic number.

• Half-life problems often involve repeated halving.

Always balance mass and atomic numbers in nuclear equations.

5. Important Points to Remember

• Radioactive decay is spontaneous and unaffected by external conditions.

• All radiation decreases with distance.

• Half-life is a statistical process.

Nuclear chemistry has wide applications but serious risks.