ICSE Class 10 Physics: Radioactivity — Complete Notes 2026

Types of Radioactive Emissions

• Alpha (α): helium nucleus (2p + 2n); charge +2; low penetration; stopped by paper
• Beta (β): fast electron from nucleus; charge −1; moderate penetration; stopped by aluminium foil
• Gamma (γ): high-energy electromagnetic radiation; no charge; most penetrating; reduced by lead/thick concrete

Nuclear Reactions and Equations

• Alpha decay: ᴬ_Z X → ᴬ⁻⁴_(Z−2) Y + ⁴₂He; mass number decreases by 4, atomic number by 2
• Beta decay: ᴬ_Z X → ᴬ_(Z+1) Y + ⁰_−₁e; mass number unchanged, atomic number increases by 1
• Gamma: no change in mass number or atomic number; just energy released

Half-Life

• Half-life (T½): time for half the radioactive nuclei to decay; characteristic of each isotope
• Formula: N = N₀ × (½)ⁿ where n = number of half-lives elapsed
• Example: if T½ = 20 years and start with 80 g, after 60 years (3 half-lives): 80 → 40 → 20 → 10 g

Uses of Radioactivity

• Nuclear medicine: I-131 for thyroid cancer treatment; Tc-99m for bone scanning
• Carbon dating: C-14 half-life 5730 years; used to date organic material (fossils, ancient wood)
• Nuclear energy: U-235 fission chain reaction; controlled in reactor; uncontrolled in atomic bomb

Safety Precautions

• Exposure time: minimise time near radioactive sources; distance reduces dose (inverse square law)
• Shielding: alpha — paper; beta — aluminium; gamma — lead or thick concrete
• Radioactive waste: India's nuclear waste stored at Trombay (BARC); requires 10,000+ year storage

ICSE Syllabus Scope

• ICSE Class 10: qualitative understanding of radioactivity types; half-life concept; uses and dangers
• Not required at ICSE: complex nuclear equations beyond alpha and beta; nuclear reactor design details
• Common questions: identify type from penetration/charge data; calculate amount remaining after n half-lives

Exam Tips

• Half-life calculations: systematic; always show each step clearly; write N₀, T½, n, final N
• Comparison table: alpha vs beta vs gamma; charge, mass, penetrating power, ionising ability
• ICSE sometimes asks: why is gamma most dangerous for humans (most penetrating, enters body easily)