eratedAt":"2026-06-09T16:10:08.191Z","modelVersion":"gemini-3.5-flash","explanationVersion":"v2"},"firstAttemptFullMarks":null},{"id":"f2f23da0-3bcd-47fe-9a7f-eb6af382a744","revisionId":"48b387fb-4607-4a01-9644-3d17925a27ae","questionNumber":null,"questionType":"LA","specification":"Nuclear fusion reactions inside stars and reactors produce energy. One proposed reaction involves a proton ($^1_1\\text{H}$) and two neutrons ($^1_0\\text{n}$) fusing to form a tritium nucleus ($^3_1\\text{H}$):\n\n$$^1_1\\text{H} + 2 \\ ^1_0\\text{n} \\rightarrow \\ ^3_1\\text{H}$$\n\nIn this reaction, $8.4\\text{ MeV}$ of energy is released.","difficulty":4,"difficultyBand":"medium","totalMarks":10,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"c10296e5-7aa6-4ee5-9b2c-6c10f32f93ce","label":"a","content":"Only one of the particles in the reaction has a non-zero binding energy. Determine the binding energy per nucleon of this particle. Explain your answer.","markscheme":"- Identifies that tritium ($^3_1\\text{H}$) is the only particle with non-zero binding energy because free protons and neutrons are unbound nucleons B1\n- Equates the total binding energy of tritium to the energy released during the reaction, which is $8.4\\text{ MeV}$ M1\n- Calculates the binding energy per nucleon by dividing by 3: $\\frac{8.4\\text{ MeV}}{3} = 2.8\\text{ MeV}$ (per nucleon) A1","marks":3,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"binding_energy_per_nucleon","label":"Use the released energy","steps":[{"type":"text","order":0,"title":"Identify the bound nucleus","content":"Tritium, $^3_1\\text{H}$, is the only particle with a non-zero binding energy. The proton and neutrons on the left are separate, **free nucleons**, so they are not bound together in a nucleus. Stating this distinction earns the **B1 mark**.","highlights":[{"text":"Only one of the particles in the reaction has a non-zero binding energy.","location":"specification"}]},{"type":"text","order":1,"title":"Use energy conservation","content":"When the free nucleons bind to form tritium, the released energy is its total binding energy. Therefore, the total binding energy of $^3_1\\text{H}$ is $8.4\\text{ MeV}$. Making this link earns the **M1 mark**.","highlights":[{"text":"In this reaction, $8.4\\text{ MeV}$ of energy is released.","location":"specification"}]},{"type":"hyper_latex","block":{"nodes":[{"latex":"$$E_{\\text{total}}=\\htmlData{anchor=released}{\\color{@sky}{8.4\\ \\text{MeV}}}$"},{"latex":"$$E_{\\text{per nucleon}}=\\dfrac{\\htmlData{anchor=total_used}{\\color{@sky}{8.4\\ \\text{MeV}}}}{3}$"},{"latex":"$$\\htmlData{anchor=answer}{\\color{@green}{E_{\\text{per nucleon}}=2.8\\ \\text{MeV per nucleon}}}$"}],"highlights":[{"color":"sky","style":"text-color","anchor":"released"},{"color":"sky","style":"text-color","anchor":"total_used"},{"color":"green","style":"text-color","anchor":"answer"}],"connections":[{"to":"total_used","from":"released","color":"sky","label":"use released energy"}]},"order":2,"title":"Divide by nucleons","description":"Binding energy per nucleon is the total binding energy divided by the number of nucleons. Tritium contains three nucleons, so dividing 8.4 MeV by 3 to obtain 2.8 MeV per nucleon earns the A1 mark."}]}],"generatedAt":"2026-07-20T15:31:52.314Z","modelVersion":"gpt-5.6-sol","explanationVersion":"v3"},"options":[]},{"id":"af56e33b-0f97-40a4-830f-b84a18b1cb96","label":"b","content":"Explain why extremely high temperatures are necessary for fusion reactions to occur between nuclei.","markscheme":"- Explains that nuclei are positively charged and experience strong electrostatic repulsion as they approach each other B1\n- Explains that extremely high temperatures provide the nuclei with very high kinetic energies M1\n- States that high kinetic energy allows nuclei to overcome the electrostatic repulsion and approach closely enough for the short-range strong nuclear force to attract and fuse them A1","marks":3,"order":1,"markingRubric":null

Nuclear and particle physics

Question 54

Nuclear and particle physics Questions

Nuclear and particle physics

Question 54

Nuclear and particle physics Questions