Nuclear Physics
Year 11 (IGCSE) 🌡️ Energy & Thermodynamics Describe atomic structure, nuclear fission, fusion and chain reactions.
⚛️ Atomic Structure and Isotopes
Every atom has a tiny, dense nucleus at the centre containing protons and neutrons, surrounded by electrons in shells.
| 🔬 Particle | ⚖️ Mass (u) | ⚡ Charge | 📍 Location |
|---|---|---|---|
| Proton (p) | 1 | +1 | Nucleus |
| Neutron (n) | 1 | 0 | Nucleus |
| Electron (e) | 1/1836 ≈ 0 | −1 | Shells/orbitals |
⚛️ Nuclear Notation
$${}^A_Z X \quad \text{where } A = \text{mass number} = p + n, \; Z = \text{atomic number} = p$$ Isotopes are atoms of the same element (same Z) with different numbers of neutrons (different A). E.g., Carbon-12 (⁶¹²C) and Carbon-14 (⁶¹⁴C) — same 6 protons, different neutron count.
☢️ Nuclear Fission
Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei, releasing a huge amount of energy and 2–3 neutrons.
☢️ Uranium-235 Fission
$${}^{235}_{92}U + {}^1_0n \rightarrow {}^{141}_{56}Ba + {}^{92}_{36}Kr + 3{}^1_0n + \text{energy}$$⚡ Chain reaction: Each fission releases 2–3 neutrons → each can trigger more fissions → exponential increase → releases enormous energy!
In a nuclear reactor, control rods absorb some neutrons to keep the reaction at a controlled, steady rate.
In a nuclear reactor, control rods absorb some neutrons to keep the reaction at a controlled, steady rate.
1 kg of uranium-235 fission releases as much energy as burning about 3,000 tonnes of coal — but produces radioactive waste instead of CO₂.
☀️ Nuclear Fusion
Nuclear fusion joins two light nuclei together to form a heavier nucleus, releasing even more energy per kg than fission.
☀️ Hydrogen Fusion (in stars)
$${}^2_1H + {}^3_1H \rightarrow {}^4_2He + {}^1_0n + \text{17.6 MeV energy}$$⚡ Mass-Energy Equivalence
$$E = mc^2 \qquad (c = 3 \times 10^8 \text{ m/s})$$☀️ The Sun: Fuses ~620 million tonnes of hydrogen per second → releases 3.8 × 10²⁶ W. Earth receives about 1.7 × 10¹⁷ W from the Sun.
Fusion needs temperatures of over 100 million °C to overcome the repulsion between nuclei. Scientists are working on fusion reactors (like ITER) as a clean, nearly limitless energy source!
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☢️ Nuclear Physics Explorer