Nuclear Science and Energy
NCERT Class 12 • Physics • Chapter "Nuclei" | NCERT Class 10 • Science • Chapter "Sources of Energy"
Nuclear Science and Energy
Ordinary chemical reactions involve only the electrons of an atom, but nuclear reactions change the nucleus itself. Because nuclear forces are far stronger than chemical bonds, these reactions release enormously more energy from the same mass of material.
Radioactivity, Fission and Fusion
- Radioactivity is the spontaneous emission of radiation by an unstable nucleus, discovered by Becquerel and studied further by the Curies.
- The three kinds of radiation are alpha, which is stopped by paper, beta, stopped by thin metal, and gamma, which needs thick lead or concrete.
- Half life is the time in which half the atoms of a radioactive sample decay.
- Nuclear fission splits a heavy nucleus such as uranium into lighter nuclei, releasing energy and more neutrons.
- Those neutrons split further nuclei, producing a chain reaction, which is controlled in a reactor and uncontrolled in a bomb.
- Nuclear fusion joins light nuclei such as hydrogen into a heavier one and releases even more energy; this is the source of the sun's energy.
- Fusion needs extremely high temperature and pressure, which is why it has not yet been harnessed for commercial power.
The Reactor and India's Programme
- A nuclear reactor has fuel rods, a moderator to slow neutrons, control rods to absorb them, a coolant and thick shielding.
- Heavy water and graphite are common moderators; boron and cadmium rods absorb neutrons and control the rate of reaction.
- The heat produced turns water into steam, which drives a turbine exactly as in a thermal plant.
- India follows a three stage nuclear programme designed around its large thorium reserves and limited uranium.
- The first stage uses natural uranium, the second uses the plutonium produced from it, and the third is meant to use thorium.
- Peaceful uses of radiation include cancer treatment, sterilisation of medical equipment, food preservation, tracing in medicine and agriculture, and dating of ancient objects.
- The main concerns are radioactive waste disposal, accident risk and the very high initial cost.
| Feature | Fission | Fusion |
|---|---|---|
| Process | Heavy nucleus splits | Light nuclei join |
| Fuel | Uranium or plutonium | Hydrogen isotopes |
| Conditions | Achievable in a reactor | Extremely high temperature |
| Example | Nuclear power plant | Energy of the sun |
Half life — the time taken for half the atoms in a radioactive sample to decay.
Exam me kaise aata hai
- Energy of the sun comes from — nuclear fusion
- Splitting of a heavy nucleus is called — nuclear fission
- Which rods control the rate of reaction — boron or cadmium control rods
- India's three stage programme is built around — thorium
UPSC/State PSC ke liye
- The moderator and the control rod do opposite jobs: the moderator slows neutrons so fission continues, while the control rod absorbs them so it does not run away.
- India's three stage programme exists because its uranium reserves are small while its thorium reserves are among the largest in the world.
Yahan confuse hote hain
✗ The sun's energy comes from fission | It comes from fusion | ✓
✗ The moderator absorbs neutrons | The moderator slows them; control rods absorb them | ✓
✗ Fusion is easier to achieve than fission | Fusion needs extreme conditions and is far harder | ✓
Ek nazar me
- Radioactivity emits alpha, beta and gamma radiation; half life measures decay.
- Fission splits heavy nuclei; fusion joins light ones and powers the sun.
- A reactor uses a moderator, control rods, coolant and shielding.
- India's three stage programme is designed around thorium reserves.