Nuclear Fission and Fusion: Flashcards
Revise mass defect, binding energy, E = mc², the binding-energy curve, chain reactions, reactors and fusion.
Nuclear Fission and Fusion: Flashcards
- QuestionWhat is the mass defect of a nucleus?Answer
Mass of the separate protons and neutrons minus the mass of the nucleus.
- QuestionWhat is binding energy?Answer
The energy needed to separate a nucleus into its protons and neutrons, E = Δm c² (Δm in kg, c in m/s, E in J).
- QuestionWhich nucleus is near the peak of the binding-energy-per-nucleon curve?Answer
Iron-56 (about 8.8 MeV per nucleon): among the most stable nuclei.
- QuestionWhy do both fission and fusion release energy?Answer
Both form nuclei with a higher binding energy per nucleon (closer to iron); the extra binding energy is released.
- QuestionWhat is nuclear fission?Answer
A heavy nucleus (e.g. uranium-235) splits into two medium nuclei, releasing 2–3 neutrons and about 200 MeV.
- QuestionWhat is a chain reaction, and what is the critical mass?Answer
Neutrons from one fission cause further fissions. The critical mass is the smallest mass of fuel that sustains the chain.
- QuestionRoles of the moderator and the control rods in a reactor?Answer
Moderator (water, graphite) slows neutrons. Control rods (boron, cadmium) absorb neutrons to control the rate.
- QuestionWhat is nuclear fusion?Answer
Light nuclei join to form a heavier one, e.g. ²H + ³H → ⁴He + n. It needs millions of degrees.
- QuestionWhy does fusion need such high temperatures?Answer
The positively charged nuclei repel each other; they must collide very fast to get close enough to fuse.
- QuestionHow do you convert u to kg, and MeV to J?Answer
1 u = 1.66054 × 10⁻²⁷ kg; 1 MeV = 1.602 × 10⁻¹³ J (and 1 u of mass ≈ 931.5 MeV).
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