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Flip to reveal answersWhat is the 'mass defect' of a nucleus?
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All 11 Flashcards — Mass-energy equivalence and binding energy
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Question
What is the 'mass defect' of a nucleus?
Answer
(Mass of the separate protons + neutrons) − (mass of the bound nucleus). The nucleus is the **lighter** one.
Question
What is the 'binding energy' of a nucleus?
Answer
The energy equivalent of the mass defect (E = mc²) — the energy needed to **pull the nucleus apart** into separate nucleons.
Question
What is 'binding energy per nucleon'?
Answer
Binding energy ÷ number of nucleons (A). It lets you **compare the stability** of different nuclei fairly.
Question
Which equation links the mass defect to the binding energy?
Answer
$E = mc^{2}$ — mass-energy equivalence (given in the data booklet). Here m is the mass defect.
Question
Fast way to convert a mass defect in u into energy in MeV?
Answer
Multiply Δm (in u) by **931.5**, because 1 u = 931.5 MeV c⁻².
Question
On the binding-energy-per-nucleon curve, what does 'higher' mean?
Answer
**More tightly bound = more stable.** The curve peaks near iron (A ≈ 56), the most stable nuclei.
Question
Why does fusion of light nuclei release energy?
Answer
It moves **up** the steep left side of the curve — the product is more tightly bound — so energy is released.
Question
Why does fission of heavy nuclei release energy?
Answer
It moves **up** the gentle right side of the curve toward iron — the products are more tightly bound — so energy is released.
Question
Which nucleus sits at the peak of the curve?
Answer
Iron (around **A ≈ 56**) — the most tightly bound, most stable nucleus.
Question
Fusion vs fission — which releases more energy per unit mass of fuel?
Answer
**Fusion** — it climbs the steep light-nuclei side, giving several times more MeV per nucleon than fission.
Question
A nucleus has Δm = 0.030 u and 4 nucleons. Binding energy per nucleon?
Answer
E = 0.030 × 931.5 ≈ 28 MeV total, then 28 ÷ 4 ≈ **7 MeV per nucleon**.
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Fission
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