Radioactivity

Definition

The spontaneous emission of radiation from the unstable nucleus of certain atoms as they decay into more stable forms.

Key points

• The three main types of radiation are alpha (a helium nucleus, least penetrating, stopped by paper), beta (electrons, stopped by aluminium), and gamma (high-energy electromagnetic waves, most penetrating, needing thick lead or concrete).
• Half-life is the time taken for half the atoms in a radioactive sample to decay; it is constant for a given isotope and ranges from fractions of a second to billions of years.
• Henri Becquerel discovered radioactivity (1896), and Marie and Pierre Curie did pioneering work, discovering polonium and radium.
• Uses include carbon-14 dating of fossils and artefacts, cancer treatment (radiotherapy), medical imaging tracers, and generating electricity in nuclear reactors.
• Radiation can damage living cells, so exposure is regulated; in India the Atomic Energy Regulatory Board oversees radiation safety.

Why it matters for CAPF

Types of radiation and their penetrating power, half-life, carbon dating, and radiation safety are standard physics facts, and radiological materials are a recognised CBRN (chemical, biological, radiological, nuclear) security threat.

Common confusion

Alpha particles are the least penetrating but most ionising, while gamma rays are the most penetrating; do not equate penetrating power with biological damage. Half-life is fixed for an isotope and is not affected by temperature or pressure.

Related concepts

concept nuclear fission and fusion, concept electromagnetic spectrum

Parent note

physics everyday