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Asked in GUJCET 2025 · Energy released in fission and fusion
Idea: the proton-proton cycle welds four protons into one helium-4 nucleus. The net effect is the sum of its steps, so add them up.
Twice: ¹₁H+¹₁H→²₁H+e⁺+ u+0.42 MeV, then e⁺+e⁻→2γ+1.02 MeV, then ²₁H+¹₁H→³₂He+γ+5.49 MeV.
Once: ³₂He+³₂He→⁴₂He+2 ¹₁H+12.86 MeV.
Product: four protons and two electrons leave one nucleus of mass number 4 and charge 4-2=2, that is ⁴₂He.
Energy: 2(0.42+1.02+5.49)+12.86=26.7 MeV.
So the blanks are ⁴₂He and 26.7 MeV.
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