Nuclear & Radioactivity
Physics · नाभिकीय और रेडियोधर्मिता
📋Quick Overview
Radioactivity is the spontaneous emission of radiation (alpha, beta, gamma) from the nucleus of an unstable atom. It was discovered by Henri Becquerel in 1896 while studying uranium. Marie Curie and Pierre Curie further studied it and discovered radium and polonium. Nuclear physics deals with the nucleus of atoms — including nuclear fission (splitting) and fusion (combining), which release enormous energy.
📖Alpha, Beta & Gamma Radiation
| Radiation | Nature | Charge | Mass | Penetrating Power | Stopped By |
|---|---|---|---|---|---|
| Alpha (α) | Helium nucleus (2p + 2n) | +2 | 4 amu (heaviest) | LEAST (weakest) | Sheet of paper, skin |
| Beta (β) | Electron (from nucleus) | -1 | Very light (1/1836 of proton) | Medium | Aluminum sheet |
| Gamma (γ) | Electromagnetic wave (like X-ray but more energetic) | 0 (neutral) | 0 (no mass) | MOST (strongest, most dangerous) | Thick lead or concrete |
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Penetrating power order: Gamma > Beta > Alpha. Ionizing power order (opposite): Alpha > Beta > Gamma. Alpha is most ionizing but least penetrating!
📝Half-Life
- •Half-life = time taken for HALF of the radioactive atoms to decay. After 1 half-life, 50% remains. After 2 half-lives, 25%. After 3, 12.5% and so on.
- •Half-life is CONSTANT for a given element — it does NOT change with temperature, pressure, or any physical/chemical condition.
- •Carbon-14 dating: C-14 has half-life of 5730 years. Used to determine age of fossils and archaeological objects.
📖Nuclear Fission vs Fusion
📝Nuclear Reactor & Nuclear Power in India
- •Nuclear reactor uses CONTROLLED fission of U-235 or Pu-239 to generate electricity. Cadmium/Boron rods absorb excess neutrons to control the chain reaction.
- •Heavy water (D₂O) is used as moderator in Indian reactors to slow down neutrons.
- •India's first nuclear power plant: Tarapur, Maharashtra (1969). Father of India's nuclear program: Dr. Homi J. Bhabha.
- •Other nuclear plants: Rawatbhata (Rajasthan), Kalpakkam (Tamil Nadu), Narora (UP), Kakrapar (Gujarat), Kudankulam (Tamil Nadu — largest).
- •Hiroshima (Aug 6, 1945) — atom bomb 'Little Boy' (Uranium). Nagasaki (Aug 9, 1945) — 'Fat Man' (Plutonium). Dropped by USA on Japan to end World War II.
- •Einstein's E = mc² explains why nuclear reactions release so much energy — a tiny mass converts to enormous energy.