CCEA A Level Physics 4.7 Nuclear Energy and 4.8 Nuclear Fission and Fusion Exam Questions

About CCEA A Level Physics 4.7 Nuclear Energy and 4.8 Nuclear Fission and Fusion

These sections end Unit A2 1: Deformation of Solids, Thermal Physics, Circular Motion, Oscillations and Atomic and Nuclear Physics. Nuclear energy uses E = Δmc^2 to link mass defect to binding energy, and the binding energy per nucleon curve to explain why both fission of heavy nuclei and fusion of light nuclei release energy. Section 4.8 covers the components of a fission reactor and their roles, the social, environmental, security and economic issues of nuclear power, and fusion research including the ITER project and methods of confining a plasma. Examiners set mass defect calculations in atomic mass units, explanations using the binding energy curve and extended writing on reactors or fusion.

What you need to know

• Mass-energy equivalence E = Δmc^2. The mass of a nucleus is less than the total mass of its separate nucleons; this mass defect corresponds to the binding energy. 1 u is equivalent to about 931 MeV.
• Binding energy per nucleon Binding energy per nucleon measures stability. The curve rises steeply for light nuclei, peaks near iron-56 at about 8.8 MeV, then falls slowly for heavy nuclei.
• Fission and fusion Fission splits a heavy nucleus such as uranium-235 (after absorbing a thermal neutron) into two smaller nuclei plus neutrons. Fusion joins light nuclei such as deuterium and tritium. Both release energy because the products have higher binding energy per nucleon.
• Fission reactor Fuel rods contain enriched uranium. The moderator (water or graphite) slows neutrons so they can cause further fission. Control rods (boron or cadmium) absorb neutrons to control the chain reaction. The coolant removes heat to make steam, and concrete shielding absorbs radiation.
• Issues of nuclear power Benefits include low carbon emissions and reliable output. Issues include long-lived radioactive waste, accident risk, security of nuclear materials and high construction and decommissioning costs.
• Fusion and ITER Fusion needs temperatures of around 10^8 K so nuclei overcome electrostatic repulsion, plus enough density and confinement time. ITER is an international tokamak using magnetic confinement; the other approach is inertial confinement using powerful lasers on a fuel pellet.

Common mistakes in 4.7 Nuclear Energy and 4.8 Nuclear Fission and Fusion

• Saying energy is released because mass is destroyed without linking it to an increase in binding energy per nucleon.
• Describing the moderator as absorbing neutrons; it slows them down, control rods absorb them.
• Forgetting to convert atomic mass units to kg before using E = Δmc^2, or not using 931 MeV per u.
• Explaining the high fusion temperature as needed to break bonds; it gives nuclei enough kinetic energy to overcome electrostatic repulsion.
• Thinking binding energy is energy stored in the nucleus that is released; it is the energy needed to separate the nucleus into its nucleons.

Try three 4.7 Nuclear Energy and 4.8 Nuclear Fission and Fusion exam-style questions