Explain gamma emission in nuclide equations
Show an excited nucleus lowering energy without changing nucleon number proton number or element.
Section 5.2.3 · Radioactive decay
Exam scope and assessment notes
Extended only (Supplement) · Physics 0972, 2026–2028. Use labelled nuclides, supplied count intervals and stated background conditions. Model drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Read nuclide notation.
- Distinguish electric charge and energy.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What happens to A and Z in gamma emission alone?
What you will learn
- Show an excited nucleus lowering energy without changing nucleon number proton number or element.
- Write gamma emission with unchanged nuclide counts and a lower nuclear energy state.
Use the excited-state label
Gamma emission releases energy from a nucleus in an excited state. A star on a nuclide label can mark that excited state. The illustrative equation ¹²₆C* → ¹²₆C + γ has unchanged A = 12 and Z = 6; gamma carries neither nucleon number nor electric charge.
Proton and neutron counts therefore stay the same. The element and isotope labels are unchanged by gamma emission alone, even though the nuclear energy has changed. A zero charge is not a zero photon energy.
Separate lower energy from absolute stability
Releasing excitation energy takes the nucleus to a lower-energy state and can make it more stable. It does not prove that every possible daughter from every preceding reaction is non-radioactive. Later nuclear changes depend on the nuclide and available states.
The equation is a labelled teaching example. It does not supply a gamma energy, a time of emission or a detector efficiency. Do not calculate these from A and Z alone.
Pause and explain
Does the star on ¹²₆C* mean one extra neutron?
Worked example
For ¹²₆C* → ¹²₆C + γ, find the change in proton and neutron counts.
Show the worked solution
- Initial Z is 6 and A − Z is 6.
- Final Z is 6 and A − Z is 6.
- Both counts are unchanged.
Answer No change: 6 protons and 6 neutrons before and after.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Complete the illustrative gamma equation ¹²₆C* → ? + γ.
Give me a hint
Keep the displayed A and Z.
Compare my reasoning
- Gamma has A = 0 and Z = 0.
- The daughter retains A = 12 and Z = 6.
- The excitation label is removed in this model.
¹²₆C.
Look for these in your work
- Preserve both counts.
- Describe lower nuclear energy.
Find neutron counts before and after this carbon-12 gamma emission.
Give me a hint
Use A − Z on both sides.
Compare my reasoning
- 12 − 6 = 6 initially.
- 12 − 6 = 6 finally.
- There is no neutron-count change.
6 before; 6 after.
Look for these in your work
- Use the same isotope labels.
- Avoid beta-minus conversion.
A report says gamma has no charge so it carries no energy. Correct it.
Give me a hint
Distinguish electromagnetic energy from electric charge.
Compare my reasoning
- A photon can carry energy.
- Gamma emission lowers nuclear energy.
- Its electric charge remains zero.
Gamma carries energy despite zero electric charge.
Look for these in your work
- Name the energy transfer.
- Keep charge and energy distinct.
Common mistakes
- Gamma changes nuclear energy.
- Zero charge does not mean zero energy.
- Do not infer a half-life from A.
What can you explain now?
Which emission is electromagnetic radiation?
Compare with the explanation
Gamma
Gamma consists of electromagnetic photons.
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Make it stick
Write gamma emission with unchanged nuclide counts and a lower nuclear energy state.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.