Radiation hazards and protection
Key idea: Irradiation exposes you to radiation; contamination puts radioactive material on or inside you. Shielding, distance and short exposure times reduce the dose, but none of them change a source's half-life.
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Guided lessons · coming soon
Guided lesson
Guided steps
- Read how ionisation can damage living cells.
- Compare sources outside and inside the body.
- Follow how an alpha emitter can reach lung tissue.
- Identify how breathing in the powder can expose living lung tissue.
- Compare radiation exposure with transfer of radioactive material.
- Decide whether storing the original source removes powder from the glove.
- Read how each protection measure reduces exposure.
- Compare shielding with decay, then find the activity after ten years.
- Find the dose ratio, then compare activity and exposure.
- Read how half-life affects storage decisions.
- Find the remaining activity and judge the disposal claim.
- Correct all three claims in the protection plan.
- Review exposure, contamination and activity distinctions, then use Practise and check.
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ContinueThe same ionisation that makes radiation useful also makes it dangerous. Radiation that ionises the molecules in a living cell can damage or kill the cell, and a large enough dose can harm a whole person. How much harm a source can do depends on what it emits, where it is, how long you are exposed to it and how long it stays active. These ideas explain why authorised work with sources uses controlled procedures and dose-limiting measures.
How radiation harms living cells
When ionising radiation passes through the body, it knocks electrons out of the molecules in cells. This can:
- kill cells, which at large doses causes burns and radiation sickness;
- damage the DNA in cells. A cell with damaged DNA may divide out of control, which can lead to cancer.
Possible effects depend on absorbed dose, dose rate, radiation type and the tissue exposed. Large doses can cause immediate injury; lower doses can increase the chance of later effects such as cancer. Radiation protection minimises unnecessary exposure; see the WHO explanation of ionising radiation and health.
Outside or inside the body
The danger from each radiation depends on whether the radioactive material is outside or inside the body.
| Radiation | External exposure | Internal exposure |
|---|---|---|
| alpha | typical alpha particles do not penetrate intact outer skin deeply; source containment still matters | an emitter within tissue can deposit energy densely over a short range |
| beta-minus | can reach and damage skin or eyes, depending on energy and conditions | can deposit energy in nearby tissue |
| gamma | penetrating photons can reach internal tissue from outside | photons may escape or deposit energy within tissue |
To compare hazards, consider activity, radiation energy, exposure time, tissue location and other emissions as well as the exposure.
Worked example 1
Why where the source is matters
Problem
Compare the alpha exposure from a source in an intact container that stops its alpha particles with exposure from alpha-emitting dust breathed into the lungs. In this example, ignore any other emissions. Explain how the barrier and receiving tissue change the risk.
Show full solution
The source on the bench
Method
The container stops the alpha particles before they reach tissue.
Reason
The stated intact container provides the barrier; typical alpha particles also have a short range in air and limited penetration of intact outer skin.
Working
Answer
outside the body: short range → no living cells reached
The dust in the lungs
Method
Dust deposited close to living lung cells emits alpha particles near that tissue.
Reason
An emitter deposited close to living cells can expose them along a short alpha track; the external container is no longer between the emitter and that tissue.
Working
Answer
internal emitter → nearby tissue can be reached
Why that is so harmful
Method
An alpha particle that stops in tissue deposits its kinetic energy over a short track.
Reason
Typical alpha tracks produce dense ionisation, so energy can be deposited within nearby living tissue.
Working
Answer
dense ionisation over a short track → possible cell damage
Quick check
Short range can limit the external alpha exposure while concentrating energy deposition near an internal emitter. Compare sources using their activity, emissions and exposure conditions as well as their radiation type.
Check your understanding 1 Identify the receiving tissue
A learner says an alpha-emitting powder is harmless because paper can stop alpha particles. The powder could be breathed in. Choose the possible exposure and explain why paper outside the body would not protect the lungs.
Show answer
A barrier protects tissue only when it lies between the source and that tissue. Breathing in radioactive material can place an emitter close to lung tissue, where its alpha radiation deposits energy over a short range. Source activity and other emissions also affect the hazard.
Irradiation and contamination
These two words describe different things.
- Irradiation means being exposed to radiation. Removing an external source or interrupting its radiation path ends exposure from that source. Exposure does not by itself mean radioactive material has been transferred; previously deposited energy and any resulting damage are not undone.
- Contamination means that radioactive material itself has got onto or into something, such as skin, clothing, food or a surface. The material keeps emitting radiation wherever it goes, so the exposure continues until it is removed or has decayed.
In approved food-irradiation processes, food does not become radioactive. Controlled irradiation and radioactive contamination are different: see the FDA explanation of food irradiation.
Check your understanding 2 Powder on a glove
Some radioactive powder spills onto a laboratory glove. The source it came from is then put away in its box. Is the glove still a hazard? Would putting a lead screen beside the glove solve the problem?
Show answer
Yes, the glove is still a hazard. It is contaminated: the radioactive powder is on it and keeps emitting radiation, wherever the original source is. Appropriate shielding may reduce radiation reaching tissue, depending on the emissions, but the powder remains. The trained contamination-control procedure determines isolation, handling and disposal; do not treat shielding as removal of the material.
Working safely with radioactive sources
Each safety measure reduces the radiation a person receives in a particular way:
| Measure | Why it works |
|---|---|
| Keep the exposure time short | less time for radiation to deposit energy in the body |
| Keep your distance; handle sources with long tongs | increases separation from the source and generally reduces radiation reaching the person under the stated arrangement |
| Use shielding | attenuates radiation; material and thickness must suit its type and energy |
| Use approved source containers and labelled controlled storage | provides suitable containment/shielding and prevents unintended use or loss |
| Never eat, drink or touch your face near sources; wash your hands afterwards | prevents radioactive material getting inside the body |
| Use the specified personal dosimeter; a film badge is one example | provides a calibrated record at its wearing position; it does not shield the wearer |
Shielding and half-life do different jobs. A shield reduces the radiation that gets out. It does not change how fast the nuclei in the source decay.
Guided practice 2
A shield changes exposure, not half-life
Problem
A sealed gamma source has an activity of 80 Bq and a half-life of 10 years. It is placed inside a lead container. Does the lead reduce the activity of the source? What will its activity be after 10 years?
Separate what the lead does from what time does
Hints
Hint 1
what lead does
The lead absorbs gamma rays after they have been emitted. Does it change how many nuclei decay each second?
Hint 2
what time does
How many half-lives are there in 10 years?
Show solution step by step
The effect of the lead
Method
The activity stays at 80 Bq. The lead only reduces the gamma radiation that gets out.
Reason
Absorbing the radiation after it is emitted does not change how fast the nuclei decay.
Working
Answer
less radiation outside ≠ lower activity
The effect of time
Method
After 10 years the activity is 40 Bq.
Reason
10 years is one half-life.
Working
Answer
80 × 1/2 = 40 Bq
Quick check
For this fixed sample, activity falls by radioactive decay. Shielding and distance reduce exposure; shorter exposure reduces accumulated dose. Removing some radioactive material would also reduce activity, because fewer nuclei remain.
Check your understanding 3 Comparing exposure times
Two identical sources give equal, steady absorbed-dose rates at the same distance and shielding. P is exposed for 20 s and Q for 80 s. Calculate Q’s dose divided by P’s. Do tongs change source activity? Does dose alone determine the harm?
Show answer
Q receives 80/20 = 4 times P’s dose at the stated equal dose rates. Tongs increase distance from the source, without changing its activity. Harm depends on radiation type and the exposed tissue as well as the absorbed dose; a dose ratio describes exposure, not a certain health outcome.
Half-life and storage
A long half-life means a fixed amount loses activity slowly; a short half-life means it loses a larger fraction over a given interval. Waste management also depends on the radionuclides, initial amounts/activity, other hazards, containment and the applicable authorised criteria. Use decay calculations alongside measurements and the authorised waste-management criteria.
Check your understanding 4 Calculate activity and judge a disposal claim
A fixed sample of one isotope starts at 128 Bq and has a half-life of 3 days. Ignore daughter activity. Find the number of half-lives and its expected activity after 12 days. A learner says that completing four half-lives proves it can now go into ordinary waste. Check the activity and whether that conclusion follows, then compare the full explanation below.
Show the steps Optional working
Show answer
Four half-lives give 128 × (1/2)^4 = 8 Bq under the stated single-isotope assumptions. The activity is reduced, not zero. Disposal still depends on the material and emissions and the relevant authorised assessment. A calculation alone does not permit handling or disposal.
Check your understanding 5 Review a proposed protection plan
A learner proposes that a film badge will block gamma rays, a screen beside spilled powder will remove contamination, and four half-lives will make every source safe to discard. Explain the error in each claim on paper or here, then compare all three with the model. You need not transcribe a paper response.
Show answer
A personal dosimeter provides a calibrated exposure record; it does not block the radiation. A suitable screen can attenuate radiation, but does not remove radioactive powder, which remains subject to the trained contamination-control procedure. Four half-lives leave 1/16 of the original isotope activity, not automatically an authorised disposal state. The material, emissions, quantities and applicable criteria remain necessary.
Common mistakes
- Calling every alpha source harmless or ranking every internal emitter by type alone. Include the way radiation reaches tissue and source/dose information.
- Treating irradiation as evidence of transferred radioactive material. The controlled irradiation examples here differ from contamination.
- Saying a lead shield makes a source decay more slowly, or reduces its activity. It only absorbs radiation after it is emitted.
- Giving “wear protective clothing” as the whole answer for gamma radiation. Ordinary clothing is not suitable gamma shielding; exposure time, distance and appropriate shielding must be considered.
- Listing safety measures without saying how each one reduces the dose.
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Syllabus and review details
- SEC G3 Physics 2027 · 2027
Content Structure, PDF page 9; Subject Content, PDF pages 10–28
Last reviewed: