Radioactivity

noun (uncountable)

/ˌreɪdiəʊækˈtɪvɪti/

Radioactivity is the spontaneous emission of ionising radiation — alpha particles, beta particles, or gamma rays — by unstable atomic nuclei as they decay toward a more stable configuration, releasing energy in the process. The rate of decay is characterised by the half-life, the time required for half of a radioactive sample to decay. India's nuclear power programme, managed by the Nuclear Power Corporation of India Limited (NPCIL), uses controlled radioactive decay of uranium-235 and thorium-232 as fuel; India holds the world's largest known reserves of thorium (~25% of global reserves), making the three-stage nuclear programme a long-term strategic priority.

✍️ Usage in a UPSC answer

India's three-stage nuclear power programme exploits the radioactivity of indigenous thorium-232 reserves, which constitute approximately 25% of global deposits, positioning the country for energy self-sufficiency beyond the hydrocarbon era.

Synonyms

nuclear decayradiant emissionradioactive decaynuclear radiationisotopic instability

Antonyms

nuclear stabilityinertnessstable isotope (conceptual opposite)

🌱 Word Family

radioactive (adjective), radioactively (adverb), radiate (verb), radiation (noun), radioisotope (noun), decay (noun/verb)

🔡 Root

Latin radius = ray, spoke of a wheel; activus = active; -ity = noun suffix (state or quality)

📜 Etymology

The term was coined by Marie Curie in 1898 (as French radioactivité) to describe the property she and Pierre Curie observed in uranium and the newly discovered elements polonium and radium. It combines Latin radius (ray) with activus (active, from agere = to act), literally 'active in emitting rays'. Henri Becquerel had first observed the phenomenon in 1896, but Curie's systematic study established the vocabulary. The word entered English by 1899.

🧠 Memory Hook

Radioactivity = radius (ray) + active — an unstable nucleus is 'actively shooting rays'. Picture a spinning wheel (radius = spoke) flinging particles outward in all directions as it tries to slow down and become stable — that frantic flinging is radioactivity.

📝 Seen in UPSC Question Papers

Prelims 2018 — Physics

Real UPSC previous-year questions whose text uses “Radioactivity” — proof this word earns its place on your list.

⚗️ General Science 📖 Seen in: Human Body Systems — Organ Systems, Ph...

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