Safety Precautions Around Radioactive Sources
Key idea: Supplementary radioactive-source safety covering time, distance, suitable shielding, contamination control, monitoring and authorised disposal.
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The core idea
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Learning objectives
- Interpret nuclear structure, isotopes and Rutherford scattering.
- Analyse random radioactive decay, activity, decay constant and half-life.
- Relate binding energy per nucleon to fission, fusion, applications and hazards.
- Apply conservation laws to nuclear equations and beta decay, including antineutrino evidence.
- Use mass-energy equivalence, mass defect and binding energy.
This page supports exam reasoning; it is not an operating procedure. Radioactive sources must be used only under authorised supervision and the institution’s written risk assessment, local rules and emergency arrangements.
1. Core protection principles
Exposure should be kept as low as reasonably achievable while still completing the authorised task.
- Time: plan first, then keep handling time as short as practicable.
- Distance: use tongs or a remote holder and maximise distance consistent with control of the source.
- Shielding: use shielding selected for the radiation type, energy and source geometry; more material is not automatically safer.
- Containment: keep sealed sources intact and prevent radioactive material entering the body or spreading onto surfaces.
For a small source that can be treated approximately as a point source, dose rate decreases roughly with the inverse square of distance. Do not apply this approximation blindly at distances comparable to the source or shield dimensions.
2. Why shielding must match the source
| Radiation | Main concern | General exam-level control |
|---|---|---|
| α | intense local ionisation after inhalation, ingestion or entry through a wound | containment; thin material stops the particles |
| β | skin and eye dose; bremsstrahlung may matter for energetic beta sources | low atomic-number material such as acrylic is commonly placed first; shielding is source-specific |
| γ | penetrating external exposure | suitable thickness of dense material or concrete, determined by the risk assessment |
Do not assume that lead is the correct first shield for every source. Shield selection depends on radiation type and energy, secondary-radiation production, source activity and the task geometry.
3. Handling, storage and monitoring
- Check source identity and condition before use without touching it directly.
- Use the designated working area, source holder and handling tools.
- Keep food and drink away and follow the required contamination-control procedure.
- Return the source promptly to its labelled, secure and appropriately shielded store.
- Maintain the source inventory and usage record required by the institution.
- Use personal dosimetry or area monitoring when specified by the risk assessment.
- If a source is damaged, missing or dropped, stop work, prevent access and notify the responsible radiation-safety person. Do not improvise recovery.
4. Waste and unwanted sources
Radioactive material is not placed in ordinary waste or disposed of by a student. Segregation, labelling, storage, transfer and disposal must follow the institution’s authorised route and the applicable regulatory requirements.
5. Common mistakes
- Writing “wear gloves” as the only control. Gloves may reduce contamination transfer but do not provide meaningful shielding from penetrating radiation.
- Saying all sources should be stored in lead. Shielding is selected for the actual source and can require a layered design.
- Confusing irradiation with contamination. Exposure to an external sealed source does not by itself make a person radioactive.
- Using inverse-square calculations without checking the point-source approximation.
- Treating safety as a memory list instead of linking each control to a named hazard and exposure route.
6. Exam method
For a safety question:
- Name the hazard: external exposure, contamination, ingestion or a damaged/missing source.
- State a specific control: reduce time, increase distance, use source-appropriate shielding or contain the material.
- Explain how the control reduces dose or prevents intake.
“Use tongs to increase the source–body distance, reducing the external dose rate while the sealed source is transferred to its holder.”
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Course and syllabus information
- Course
- GCE A-Level H2 Physics
- Edition
- GCE A-Level H2 Physics 2027