Radioactive Contamination, Hazards and Uses

Two situations put people at risk from radiation, and the exam repeatedly tests the difference between them.

Radioactive contamination is the unwanted presence of materials containing radioactive atoms on or in other materials. A contaminated object has radioactive atoms stuck to it or inside it, so it becomes a source of radiation itself. The hazard comes from the decay of the contaminating atoms, and it continues for as long as those atoms keep decaying.

Irradiation is the process of exposing an object to nuclear radiation from an outside source. The key point is that the irradiated object does not become radioactive. Once the source is taken away or switched off, the irradiation stops.

Contamination = radioactive atoms are on or in the object. Irradiation = radiation reaches the object from outside, but leaves no radioactive atoms behind.

A useful test question: if you removed the object to a clean room, would it still give out radiation? A contaminated object would; an irradiated object would not.

Because contamination and irradiation work differently, their hazards differ, and which type of radiation is involved changes how serious each one is.

Feature	Contamination	Irradiation
Radioactive atoms present on/in object?	Yes	No
Object becomes a radiation source?	Yes	No
Does the hazard stop when the source is removed?	No, it continues as atoms decay	Yes, it stops immediately
Most dangerous radiation type	Alpha (inside the body)	Gamma (penetrates from outside)

The type of radiation matters a great deal, and it flips depending on whether the source is inside or outside the body.

• Inside the body (contamination): alpha is the most dangerous. It is strongly ionising but has a very short range, so once it is in direct contact with living tissue it causes intense, localised damage.
• Outside the body (irradiation): gamma (and to a lesser extent beta) is the most dangerous, because alpha cannot even penetrate the skin, while gamma passes easily through the body from an external source.

The same property, strong ionising power over a short range, makes alpha the least dangerous outside the body but the most dangerous once inside it.

Because the two hazards are different, the sensible precautions are different too. Scientists and workers who handle radioactive sources choose precautions to match the risk.

Protecting against irradiation (external exposure):

• Keep sources in lead-lined boxes when not in use.
• Handle sources with long-handled tongs to increase distance.
• Stand behind lead or concrete shielding, or limit the time spent near the source.

Protecting against contamination (getting atoms on or in you):

• Wear protective clothing, gloves and, where needed, masks so radioactive atoms cannot settle on skin or be breathed in.
• Work inside sealed glove boxes for the most dangerous sources.
• Wash thoroughly and monitor for contamination after handling sources.

Distance, time and shielding reduce the dose from irradiation. Barriers such as gloves, clothing and glove boxes stop radioactive atoms getting onto or into the body, which is what prevents contamination.

The effects of radiation on the human body are serious, so the conclusions scientists draw about them have to be trustworthy.

When scientists study how radiation affects humans, they publish their findings and other scientists check that work. This checking by other experts in the field is called peer review.

Peer review matters because:

• A single study can contain mistakes, bias, or results that happened by chance.
• Other scientists can repeat the experiments and test whether the same results appear.
• Sharing findings openly lets the whole scientific community build a reliable, agreed picture rather than relying on one team's claim.

Conclusions about the effects of radiation on humans are only accepted after they have been published and independently checked by other scientists. This is how the risks used to set safety rules become reliable.

Without peer review, faulty conclusions could lead to safety limits that are either too relaxed (putting people at risk) or too strict (blocking useful medical treatments).

(Separate Physics only) This slide and those that follow, on background radiation, half-life and medical uses, are part of section 4.4.3, which is assessed in Physics but not in Combined Science.

Background radiation is the low-level radiation that is around us all the time. It comes from two kinds of source.

Source type	Examples
Natural	Rocks and soil (especially radon gas), cosmic rays from space, food and drink
Man-made	Fallout from past nuclear weapons testing, waste and accidents from the nuclear industry, some medical procedures

Most background radiation is natural. The amount a person receives depends on where they live and what they do:

• Location: areas with granite rock (such as parts of Cornwall) release more radon gas, giving a higher natural dose.
• Occupation: radiographers, nuclear-industry workers and airline crew (more cosmic rays at altitude) receive higher doses than most people.

Radiation dose, which measures the risk of harm to body tissue, is measured in sieverts (Sv), where 1000 millisieverts (mSv) = 1 Sv.

You do not need to recall the unit of radiation dose for the exam, but you should understand that dose measures the risk of harm and depends on both occupation and location.

Radioactive isotopes have a huge range of half-lives, from fractions of a second to billions of years, and this directly affects how hazardous each one is. (The half-life is the time taken for the number of radioactive nuclei, or the activity, to halve.)

• A source with a short half-life decays quickly. It gives out radiation at a high rate at first, so it is very hazardous in the short term, but it soon becomes far less active and much safer.
• A source with a long half-life decays slowly. Its activity is lower at any moment, but it stays radioactive for a very long time, so it remains a hazard for centuries or longer, which is why long-lived nuclear waste must be stored so carefully.

Worked reasoning example. Two contamination spills release the same number of radioactive atoms. Source A has a half-life of 8 days; source B has a half-life of 24 000 years.

• After a few months, source A has gone through many half-lives, so its activity has dropped enormously and the immediate danger has largely passed.
• Over the same few months, source B has barely changed. Its activity stays almost constant and it will remain hazardous for tens of thousands of years.

Short half-life means intense but brief hazard. Long half-life means weaker but very long-lasting hazard. Neither is automatically "safe": it depends on how long the source stays near people.

Nuclear radiation is used in medicine in two main ways, and each use has to be weighed against its risks.

Exploration of internal organs. A patient is given a radioactive substance (a tracer, often a gamma emitter with a short half-life) that collects in the organ being studied. A detector outside the body picks up the gamma radiation and builds an image, showing how well the organ is working without surgery.

Control or destruction of unwanted tissue. Carefully targeted radiation is used to kill cancer cells. A tumour can be treated with beams of gamma radiation aimed from outside, or with radioactive sources placed close to it, so that the dose destroys cancerous tissue while sparing as much healthy tissue as possible.

Evaluating the uses. These treatments expose the patient to radiation, which carries its own small risk of harm. Doctors and patients weigh this up:

• The benefit of diagnosing a disease early or destroying a tumour can be life-saving.
• The risk from the radiation dose is usually far smaller than the risk of leaving the illness untreated.
• Perceived risks (how dangerous people feel radiation is) are often larger than the actual measured risk, so decisions should be based on data and on the likely consequences, not on fear alone.

Judging a medical use of radiation means comparing its benefit against the actual dose and its consequences, not the perceived danger. For a seriously ill patient the benefit usually outweighs the risk.

1. Saying an irradiated object becomes radioactive

Irradiation does not make an object radioactive. Only contamination, where radioactive atoms are actually present on or in the object, makes it a source of radiation.

2. Claiming alpha is always the safest

Alpha is the least penetrating outside the body, so it is the least dangerous for external irradiation. But if alpha-emitting atoms contaminate the inside of the body, alpha is the most dangerous because of its strong ionising power at close range. Always state whether the source is inside or outside the body.

3. Muddling the precautions

Shielding, distance and limiting time reduce the dose from an external source (irradiation). Gloves, protective clothing and glove boxes stop radioactive atoms getting onto or into you (contamination). Match the precaution to the type of hazard.

4. Thinking a long half-life means more dangerous

A long half-life does not mean higher activity. It means the source stays active for longer at a lower rate. A short-half-life source is more intensely radioactive at first. The overall hazard depends on both the activity and how long the source is present.

5. Ignoring peer review in "why publish" questions

If asked why findings on radiation are published, say that other scientists check and repeat the work (peer review) so the conclusions can be trusted, not just that "people should know".