Nuclear Stability: Flashcards
Revise the strong force, the band of stability, predicting decay type, magic numbers and decay series.
Nuclear Stability: Flashcards
- QuestionWhat holds the nucleus together?Answer
The strong nuclear force: a very short-range attraction between all nucleons.
- QuestionWhy do heavier nuclei need more neutrons than protons?Answer
Neutrons add strong-force attraction without adding electrostatic repulsion between protons.
- QuestionWhat is the N/Z ratio of stable light nuclei, and of stable lead?Answer
About 1 for light nuclei (up to Z ≈ 20); about 1.5 for lead-206 (124/82).
- QuestionAbove which atomic number are all nuclei radioactive?Answer
Z = 83 (bismuth): every element beyond it is radioactive.
- QuestionHow does a nucleus with too many neutrons decay?Answer
Beta-minus decay: a neutron becomes a proton and an electron is emitted.
- QuestionHow does a nucleus with too many protons decay?Answer
Positron emission (β⁺) or electron capture: a proton becomes a neutron.
- QuestionHow do very heavy nuclei (Z above 83) usually decay?Answer
Alpha decay (losing 2 protons and 2 neutrons).
- QuestionName the magic numbers.Answer
2, 8, 20, 28, 50, 82, 126 (protons or neutrons).
- QuestionHow many α and β⁻ decays take U-238 to Pb-206?Answer
8 α (mass falls by 32) and 6 β⁻.
- QuestionPredict how carbon-14 decays.Answer
β⁻ (too many neutrons): ¹⁴C → ¹⁴N + e⁻.
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