GCSE Physics: Radioactivity Guide

Atomic structure and isotopes

An unstable, radioactive isotope has an unstable nucleus that decays, releasing radiation to become more stable, often forming a different element in the process.

Types of radiation

Alpha particles are large and strongly ionising but stopped by paper or skin. Beta particles are smaller, more penetrating, and stopped by a few millimetres of aluminium. Gamma rays are the most penetrating and require thick lead or concrete to block.

Half-life

Half-life is the time taken for half of the radioactive nuclei in a sample to decay. After each half-life, the remaining activity halves again, which is why radioactivity decreases but never quite reaches zero.

Uses and dangers

Radiation is used in medicine (diagnosis and treatment), industry (checking material thickness) and power generation, but exposure can damage living cells, so appropriate types and doses must be carefully controlled.

Common mistakes

• Mixing up the penetrating power and ionising power of alpha, beta and gamma radiation — they're roughly opposite (most ionising is least penetrating).
• Thinking half-life means "the time for all the radioactivity to disappear."
• Confusing radioactive contamination (particles present) with irradiation (exposure to radiation without particles remaining).