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ATOMIC STRUCTURE · CHAPTER 8 OF 12
How can radiation be hazardous?
A source outside the body and radioactive material inside it can pose very different hazards. To judge the risk, we need to know what the radiation is, where it comes from and how much exposure occurs.
By the end, you’ll be able to…
- explain how ionising radiation can damage cells and DNA
- distinguish irradiation from radioactive contamination
- compare internal and external exposure to different radiations
- explain precautions using time, distance, shielding and contamination control
- interpret dose data and explain how half-life affects hazards
- evaluate claims using evidence and peer review.
Ionisation can change living cells
Ionising radiation can remove electrons from atoms and molecules. The resulting changes can damage important molecules, including DNA.
A cell may repair the damage, die or survive with a change to its DNA—a mutation. Some mutations can lead to uncontrolled cell division and cancer. Exposure does not mean that cancer will definitely develop.
From an interaction to possible damage
Watch an alpha particle remove an electron from an atom. Then see how ionisation can lead to possible DNA damage.
What can happen?
Cells can repair some damage successfully. Not every radiation interaction causes lasting harm.
What can happen?
Severe damage can kill cells. If enough cells are affected, tissues can be damaged.
What can happen?
A surviving cell may retain altered DNA. Some mutations increase cancer risk; a mutation does not always cause cancer.
* This is a simplified model. The atom and DNA are shown at different scales. The electron travelling towards the DNA illustrates one possible route to further ionisation; DNA damage is not inevitable.
Irradiation: exposed to radiation
Irradiation means exposure to radiation from a source. Radioactive material does not have to touch or enter the object being irradiated.
When that external source is removed or shielded, the exposure from it stops or is reduced. Any damage already caused is not automatically undone.
Contamination: radioactive material is present
Radioactive contamination is the unwanted presence of material containing radioactive atoms on a surface or inside something. Dust, liquid or gas can carry it.
The contaminating material can keep emitting radiation where it remains. Moving the original source away does not necessarily remove the contamination.
Move the original source away. What remains?
Compare irradiation with contamination. Select the button to remove the original source from both scenes; select again to reset.
Irradiation
Contamination
* The pink circles on and inside the contaminated object represent pieces of material containing radioactive atoms, not individual electrical charges. Arrows represent radiation.
Radiation or radioactive material?
Inside or outside the body?
Alpha particles are strongly ionising but have a short range. An external alpha source usually cannot send its particles through the outer dead layer of intact skin to living tissue. If alpha-emitting material is inhaled, swallowed or enters a wound, it can irradiate nearby living cells directly.
Beta radiation can penetrate skin to a limited depth and can damage skin and eyes. Gamma radiation is more penetrating and can irradiate deeper tissues from outside the body. Internal beta and gamma emitters can also be hazardous.
The source’s position changes the hazard
Compare the same radiation outside and inside tissue. Select a scenario to see how far the radiation penetrates. Paths illustrate penetration, not exact doses or ranges.
Alpha source outside intact skin
Alpha-emitting material inside tissue
Gamma source outside the body
Gamma-emitting material inside tissue
* Pink circles represent radioactive material, not individual alpha particles or electrical charges. Cell outlines, skin thickness and radiation paths are schematic. No dose or universal “most dangerous” ranking can be read from these drawings.
Reduce exposure: time, distance and shielding
Spend less time near a source, increase distance and use appropriate shielding. These measures reduce the radiation reaching a person; they do not switch off nuclear decay.
Use remote handling tools and suitable shielded storage. To prevent contamination, keep sources contained and use suitable protective clothing and procedures. Gloves can help prevent material transfer; ordinary gloves are not effective shielding against penetrating gamma radiation.
What does each precaution actually do?
Select a precaution. Connect it to the route by which exposure occurs.
Limit the time exposed
Increase the separation
Put the right absorber in the path
Keep radioactive material from spreading
* These are principles for supervised use with appropriate equipment and procedures. The drawings do not specify shield thicknesses or authorise handling a source. The animations are schematic rather than measurements of actual radiation dose.
Activity is not dose
Activity, in becquerels (Bq), measures decays per second in a source. It does not by itself tell us how much radiation reaches a person or how much harm an exposure could cause.
Radiation dose in sieverts (Sv) is used to assess the potential biological effects of exposure. The radiation type, energy absorbed and tissues exposed matter. At GCSE, dose data help us compare risks; they do not predict exactly what will happen to one person.
Converting dose units:
1 mSv = 1000 µSv
For a constant dose rate:
Keep units consistent. A dose rate in µSv/h must be multiplied by time in hours.
Three worked examples
Calculate dose in millisieverts:
A hypothetical exposure gives 0.004 Sv.
Dose in mSv = dose in Sv × 1000
Dose = 0.004 × 1000
Dose = 4 mSv
Calculate dose:
A steady dose rate is 6 µSv/h. Exposure lasts 30 min = 0.5 h.
Dose = dose rate × time
Dose = 6 × 0.5
Dose = 3 µSv
Calculate total dose:
Two hypothetical exposures give 0.12 mSv and 80 µSv.
Total dose = first dose + second dose
80 µSv = 0.08 mSv; total = 0.12 + 0.08
Total dose = 0.20 mSv
Same dose rate. Different exposure time.
Use a constant rate of 12 µSv/h. Select the exposure time and compare the dose.
* An illustrative constant-rate comparison on the same dose scale. No safety threshold is implied.
How does half-life affect the hazard?
A short half-life means the activity falls rapidly. For the same initial number of nuclei, a shorter-half-life isotope has a higher initial activity: more nuclei decay per second.
A long half-life means the radioactive material can remain a concern for much longer. But half-life alone does not rank the hazard: initial activity, radiation type and energy, amount present and exposure route also matter.
Contaminating material may also be removed from the body or environment. How long it remains present is not always the same as its radioactive half-life.
Same initial activity. Which falls faster?
Two hypothetical sources start at 800 Bq. Source A has a half-life of 6 h; source B has a half-life of 24 h. Predict their activities after one day.
Source A
800 Bq · half-life 6 h
Source B
800 Bq · half-life 24 h
A: 50 Bq. Four half-lives: 800 → 400 → 200 → 100 → 50.
B: 400 Bq. One half-life: 800 → 400.
A’s activity falls more quickly. Neither value alone establishes that the source is safe to handle or dispose of. Radioactive daughter products could also matter.
* Equal initial activities, not equal numbers of radioactive nuclei. Values refer to the isotope being studied; daughters are excluded from the numerical model.
Evaluate the evidence, not just the headline
When comparing risk, ask what dose was received, which tissues were exposed, what radiation was involved and how long the exposure lasted. A natural source is not automatically harmless, and a human-made source is not automatically more hazardous.
Scientists publish and share research so other researchers can examine the methods, measurements and conclusions. Peer review checks the work before publication; independent studies and repeat measurements can test whether the findings hold up.
Look for adequate sample sizes, suitable comparison groups and uncertainty. A small difference does not automatically establish a cause, and peer review is not a guarantee that a conclusion can never change.
Does this comparison prove a risk?
A report says, “Two people who worked near radiation sources became ill, so the radiation must have caused both illnesses.” It gives no dose records or comparison group.
Check your understanding
Choose one answer for each question. Feedback appears underneath.
“An alpha source has been removed from the room, so radioactive dust on a sleeve is no longer hazardous. A pair of gloves would block every kind of radiation anyway.” Explain the errors and suggest appropriate precautions.
Distinguish material transfer from irradiation. Include a route by which the dust could become an internal hazard.
Reveal the answer
The dust is contamination. It remains a source of radiation on the sleeve after the original source is removed.
Alpha particles have a short range, but the material could be inhaled, swallowed or enter a wound, bringing it close to living tissue.
Gloves can reduce contamination of the hands, but ordinary gloves do not block all radiation, especially penetrating gamma radiation.
Prevent the material spreading, avoid transfer into the body, and use appropriate supervised contamination-control procedures. Time, distance and suitable shielding address exposure; simply moving the original source does not remove the dust.
CHAPTER 8
Chapter summary
- Ionisation can damage cells and DNA, kill cells or cause mutations that may increase cancer risk.
- Irradiation is exposure to radiation; contamination is unwanted radioactive material being present.
- Internal alpha-emitting contamination can be especially hazardous to nearby tissue; gamma can penetrate from outside.
- Reduce exposure using time, distance and appropriate shielding. Prevent contamination by containing material and using suitable procedures.
- Activity in Bq is different from dose in Sv. Use consistent dose and time units.
- Half-life affects how activity changes and how long a source remains a concern; it is not the only risk factor.
- Evaluate evidence, uncertainty and comparison groups; publication and peer review allow scientific scrutiny.