Radioactivity
Nuclear radiation, half-life, and uses of radioactivity
The nucleus contains protons and neutrons. Proton number (Z) = atomic number. Nucleon number (A) = protons + neutrons.
Types of nuclear radiation:
| Type | Nature | Penetrating power | Ionising power |
|------|--------|-----------------|----------------|
| Alpha (α) | 2 protons + 2 neutrons | Stopped by paper | Very high |
| Beta (β) | Fast electron | Stopped by thin aluminium | Medium |
| Gamma (γ) | EM radiation | Reduced by thick lead | Low |
Half-life: Time for half the radioactive nuclei to decay. After n half-lives, activity = original × (½)ⁿ.
Uses:
- Alpha: smoke detectors (ionise air)
- Beta: checking thickness of paper/steel
- Gamma: sterilising medical equipment, cancer treatment, food preservation
Background radiation — cosmic rays, rocks (radon gas), medical, nuclear industry.
Nuclear equations: Balancing A and Z. Alpha decay: A decreases by 4, Z by 2. Beta decay: Z increases by 1, A unchanged.
Key Points to Remember
- 1Alpha: paper stops it; Beta: aluminium; Gamma: lead needed
- 2Half-life: time for half of nuclei to decay
- 3Alpha: smoke detectors; Beta: thickness gauges; Gamma: medical
- 4Background radiation is natural and always present
Pakistan Example
Shaukat Khanum Hospital — Gamma Radiation Saving Pakistani Lives
Shaukat Khanum Memorial Cancer Hospital uses gamma radiation (Cobalt-60) for radiotherapy — targeting tumours while shielding healthy tissue using thick lead barriers. Pakistan's PAEC (Atomic Energy Commission) also uses radiation for food preservation — irradiating spices and mangoes kills bacteria without chemicals. The half-life of Cobalt-60 is 5.3 years, meaning it must be replaced periodically — real half-life calculations.
Quick Revision Infographic
Physics — Quick Revision
Radioactivity
Key Concepts
Shaukat Khanum Hospital — Gamma Radiation Saving Pakistani Lives
Shaukat Khanum Memorial Cancer Hospital uses gamma radiation (Cobalt-60) for radiotherapy — targeting tumours while shielding healthy tissue using thick lead barriers. Pakistan's PAEC (Atomic Energy Commission) also uses radiation for food preservation — irradiating spices and mangoes kills bacteria without chemicals. The half-life of Cobalt-60 is 5.3 years, meaning it must be replaced periodically — real half-life calculations.