Explain gamma emission in nuclide equations
Show an excited nucleus lowering energy without changing nucleon number proton number or element.
Section P5.2.3 · Radioactive decay
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
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.
Sources for this lesson
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.
Try a topic test
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Test this topic →From guided practice to a new situation
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.