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UPPCS Physics Gap Sheet: Nuclear Physics and Radiation.
UPPCS has asked 22 of these. 11 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
The nucleus contains protons and neutrons. Isotopes share a proton number but differ in neutron number. Radioactive decay changes an unstable nucleus; chemical reactions mainly rearrange electrons and do not alter the nucleus.
Fission splits a heavy nucleus, while fusion joins light nuclei. A reactor controls a chain reaction and removes its heat. Fuel, moderator, control rods and coolant perform different jobs and must not be confused.
✅ Already asked (22)
Nucleus and decay
- Proton and neutron · Proton has positive charge; neutron is electrically neutral; both occur in nuclei.
- Isotopes · Same element and proton number, but different neutron numbers and masses.
- Isobars · Different elements with the same mass number but different atomic numbers.
- Alpha radiation · An alpha particle is a helium nucleus with two protons and two neutrons.
- Gamma radiation · A nucleus emits an uncharged high-energy photon; atomic and mass numbers stay unchanged.
- Half-life · Time for half the undecayed radioactive nuclei in a large sample to decay.
Fission, fusion and reactors
- Nuclear fission · A heavy nucleus splits, releasing energy and often neutrons.
- Solar fusion · The Sun gains energy mainly by converting hydrogen into helium through fusion.
- Controlled chain reaction · A power reactor maintains a controlled fission chain reaction.
- Moderator · Graphite, ordinary water or heavy water can slow neutrons in suitable reactor designs.
- Heavy water · Contains deuterium; some reactors use it as moderator and coolant.
- Coolant · Removes heat from the reactor core; its role differs from neutron moderation.
- Enriched uranium · Has a higher fraction of uranium-235 than natural uranium.
- Breeder reactor · Produces more fissile material than it consumes by converting fertile material.
- Thorium-232 · A fertile material that can be converted to fissile uranium-233; it is not itself a usual fissile fuel.
Applications and particle facts
- Carbon-14 dating · Dates once-living material; it does not directly date every type of rock.
- Cobalt-60 · A gamma source used in some cancer-treatment and sterilisation systems.
- Iodine-131 · Used in selected thyroid diagnosis and treatment.
- Positron · The electron's antiparticle; it has equal mass and positive charge.
- Neutrino · An electrically neutral particle that interacts very weakly with matter.
- Higgs boson · Associated with the Higgs field; popularly called the God particle.
Further nuclear distinctions
- Fissile and fertile materials · Uranium-235 is fissile; uranium-238 is fertile and can help produce plutonium-239.
❌ Not asked yet (11)
Items marked 'asked in other exams' have come in UPSC or other state exams, not yet in UPPCS.
🔒 11 items not asked yet
Nucleus and decay: 3 · Fission, fusion and reactors: 1 · Further nuclear distinctions: 7
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⚠️ A moderator slows neutrons; control rods absorb them. Gamma rays carry no electric charge, but they are still ionising radiation.
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