Safety PrecautionsCambridge IGCSE Physics: Revision notes
Section 1
Why radioactive sources are hazardous
Ionising nuclear radiation can damage living cells, causing:
- Cell death
- Mutations (changes to DNA)
- Cancer
The severity of the hazard depends on the type of radiation (its ionising power and penetrating ability) and on how the exposure occurs — for example, whether the source is outside the body or has been swallowed/inhaled.
Section 2
Penetrating power determines the precautions needed
Recall the relative penetrating abilities of the three types of radiation:
| Type | Penetrating ability | Shielding needed |
|---|---|---|
| Alpha | Weak — stopped by paper or a few cm of air | Minimal external shielding, but dangerous if inhaled/swallowed |
| Beta | Moderate — stopped by a few mm of aluminium | Aluminium sheeting |
| Gamma | Strong — barely absorbed even by thick material | Thick lead or concrete |
Safety precautions must always be matched to the specific type of radiation a source emits — using the wrong shielding material could allow a large dose to pass through.
Don't assume alpha radiation is always 'safe' just because it barely penetrates the skin — it is the most strongly ionising and most dangerous type if a source gets inside the body.
Section 3
The three key precautions
Whatever the source, exposure to ionising radiation is reduced using three general strategies:
- Reducing exposure time — spend as little time as possible near the source
- Increasing distance — radiation intensity falls off rapidly with distance from the source
- Using shielding — placing an absorbing material (matched to the radiation type) between the source and the person
These three precautions apply to all ionising radiation, whether from a laboratory source, medical equipment, or industrial use.
Memorise the three precautions as time, distance, shielding — nearly every safety question can be answered using one or more of these.
Section 4
Storing and moving radioactive materials safely
Radioactive materials must be moved, used and stored in ways that keep people safe, for example:
- Storing sources in shielded, lead-lined containers when not in use
- Using remote handling tools (e.g. tongs) to keep distance between the user and the source
- Clearly labelling containers and restricting access to trained personnel
- Choosing sources with an appropriate half-life and radiation type for the task, so that unnecessary long-term hazards are avoided
A school laboratory keeps radioactive sources in a lead-lined box and uses tongs, never bare hands, to move them into position for an experiment.
Section 5
Applications where safety choices matter
The type of radiation and its half-life together determine how safely a source can be used for a given application:
- A long half-life source used continuously (e.g. in a thickness gauge) needs stronger, permanent shielding because it stays active for a long time
- A short half-life source used briefly (e.g. in medical diagnosis) reduces long-term risk to the patient, since it decays away quickly after use
- Sources chosen for their penetrating power (e.g. gamma for sterilising food) still require precautions for the people operating the equipment, even though the target itself is meant to be exposed
Must Know
- Ionising radiation can cause cell death, mutations and cancer
- The three key precautions are: reduce exposure time, increase distance, use shielding
- Shielding must match the radiation type: paper/air for alpha, aluminium for beta, thick lead/concrete for gamma
- Alpha is weakly penetrating externally but very dangerous if a source is inhaled or swallowed, due to its strong ionising power
- Radioactive materials must be stored, moved and used safely (e.g. shielded containers, remote handling tools)
- Half-life affects safety planning: long half-life sources need durable shielding for continuous use; short half-life sources limit long-term exposure risk
That's the notes covered.
Carry on to the next subtopic.