Which nuclear decay mode decreases the atomic number Z of a parent nucleus by 1 while leaving the mass number A unchanged?
Answer and explanation
Correct answer: D. Positron emission (beta-plus decay) or electron capture
- Step 1: In beta-plus decay: p -> n + e+ + nu_e. A proton converts to a neutron. Step 2. Therefore, Z decreases by 1 (Z' = Z - 1), and mass number A remains constant. Electron capture achieves the same result: p + e- -> n + nu_e. Answer: Positron emission (beta-plus decay) or electron capture. Why not the others: Beta-minus increases Z by 1; alpha decay decreases Z by 2 and A by 4; gamma decay changes neither.
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