Questions: Gamma Radiation and Nuclear Transitions
2 questions to test your understanding
Score: 0 / 2
Question 1 Short Answer
A nucleus undergoes beta decay to an excited daughter state, then the daughter emits a gamma ray. How many changes in Z and A occur in total?
Think about your answer, then reveal below.
Model answer: Beta decay changes Z by ±1 (and A stays constant). Gamma emission changes neither Z nor A. Total: Z changes by ±1, A unchanged.
Beta-minus decay converts a neutron to a proton (Z increases by 1), beta-plus converts a proton to neutron (Z decreases by 1), while A = Z + N is unchanged in both. Gamma emission is purely an energy release — no nucleon number or charge changes. The sequence is extremely common in nuclear decay chains: a nucleus beta-decays to an excited daughter, which then gamma-decays to the daughter's ground state.
Question 2 Short Answer
Why does a 0⁺ → 0⁺ nuclear transition (both initial and final states have spin 0 and even parity) not proceed by gamma emission?
Think about your answer, then reveal below.
Model answer: A photon carries at minimum one unit of angular momentum (L ≥ 1). A 0 → 0 transition requires ΔJ = 0, but no photon with angular momentum 0 exists — the electromagnetic field cannot carry zero angular momentum. Therefore single-photon emission is strictly forbidden for 0⁺ → 0⁺ transitions.
This selection rule is absolute, not just a suppression. The transition can still proceed via internal conversion (where the nucleus's energy is transferred to an atomic electron) or by rare two-photon emission, but these are much slower. The 0⁺ → 0⁺ case arises notably in even-even nuclei and is an important test of nuclear structure models.