Contamination vs Irradiation

This lesson explains the crucial difference between radioactive contamination and irradiation, the risks associated with each, the safety precautions taken by workers, and the practical uses of radiation in medicine, industry and agriculture. This is an important topic in the Edexcel GCSE Combined Science specification (1SC0) that is frequently tested in exams.

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Irradiation

Irradiation is the process of exposing an object (or person) to radiation from a source outside the body. The object does not become radioactive itself.

Key point	Detail
Definition	Exposure to radiation from an external source
Does the object become radioactive?	No
Can it be controlled?	Yes — by removing the source, increasing distance, or using shielding
Example	Having an X-ray at a hospital; standing near a sealed radioactive source

Controlling Irradiation

The three key principles are:

1. Time — minimise the time spent near the source.
2. Distance — maximise the distance from the source (radiation intensity decreases with distance).
3. Shielding — place absorbing material (e.g. lead, concrete) between the source and the person.

Exam Tip: Remember the three words: time, distance, shielding — these come up in almost every question about radiation safety.

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Contamination

Radioactive contamination occurs when radioactive material is deposited on or inside the body (or an object). The contaminating material continues to emit radiation.

Key point	Detail
Definition	Radioactive material is deposited on or inside the body or object
Does the object become a source of radiation?	Yes — it now has radioactive material on/in it
Can it be easily removed?	Not always — internal contamination is very difficult to remove
Example	Breathing in radioactive dust; spilling a radioactive liquid on skin; ingesting contaminated food

Why Is Contamination Particularly Dangerous?

• The radioactive material is in contact with (or inside) the body.
• It continues to irradiate surrounding tissue for as long as it remains.
• Alpha emitters are especially dangerous when inhaled or ingested — they are strongly ionising and can cause severe damage to internal organs, despite being stopped by skin from the outside.

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Comparing Irradiation and Contamination

Feature	Irradiation	Contamination
Source location	Outside the body	On or inside the body
Does the person become radioactive?	No	Yes (temporarily)
Most dangerous type of radiation	Gamma (most penetrating)	Alpha (most ionising when inside the body)
How to reduce risk	Time, distance, shielding	Protective clothing, gloves, masks; sealed sources; decontamination procedures
Easy to stop?	Yes — remove the source	Difficult — especially if internal

graph TD
    A["Radiation exposure"] --> B["Irradiation<br/>(external source)"]
    A --> C["Contamination<br/>(material on/in body)"]
    B --> D["Not radioactive afterwards"]
    C --> E["Radioactive material remains<br/>and continues to emit"]

Exam Tip: A 6-mark question may ask you to compare irradiation and contamination and explain which is more dangerous in a given scenario. Always consider the type of radiation — alpha is most dangerous for contamination, gamma for irradiation.

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Safety Precautions

In the Laboratory

Precaution	Reason
Use long-handled tongs to handle sources	Increases distance between the source and the body
Point the source away from people	Reduces irradiation
Keep exposure time short	Reduces total dose
Store sources in lead-lined containers	Shielding reduces irradiation when not in use
Do not eat or drink near sources	Prevents ingestion (contamination)
Wash hands after handling	Removes any contaminating material
Use sealed sources where possible	Prevents radioactive material from escaping

In Industry and Medicine

Precaution	Detail
Radiographers stand behind lead screens	Shielding from repeated X-ray exposure
Workers wear dosimeters (film badges)	Monitor cumulative radiation dose
Radiation areas are clearly marked with warning signs	Alert people to the hazard
Robotic handling of highly active sources	Eliminates human exposure

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Uses of Radiation

Radioactive sources are carefully chosen based on their type of radiation and half-life for each application.

Medical Uses

Use	Type of radiation	Details
Medical tracers (e.g. technetium-99m)	Gamma	Injected or swallowed; detected outside the body to diagnose problems. Must have a short half-life (hours) to limit patient dose.
Cancer treatment (radiotherapy)	Gamma (or beta)	Focused beams directed at tumours to kill cancer cells. Source rotated around the patient to minimise damage to healthy tissue.
Sterilisation of surgical instruments	Gamma	Penetrates packaging to kill bacteria without heating. Instruments remain sealed and sterile.

Industrial Uses

Use	Type of radiation	Details
Thickness monitoring (paper/metal)	Beta (for paper), Gamma (for metal)	Source on one side, detector on the other. If too thick, less radiation gets through — machinery adjusts automatically.
Detecting leaks in pipes	Gamma (or beta)	Radioactive tracer added to fluid; detected above ground where it leaks out.
Smoke detectors	Alpha	Alpha particles ionise air, allowing a current to flow. Smoke absorbs alpha particles, reducing the current and triggering the alarm. Uses americium-241 (long half-life).

Agricultural and Environmental Uses

Use	Type of radiation	Details
Carbon dating	Beta (from carbon-14)	Measures the ratio of carbon-14 to carbon-12 in once-living material to estimate its age. Half-life of carbon-14 ≈ 5730 years.
Sterilising food (irradiation)	Gamma	Kills bacteria on food to extend shelf life. The food does not become radioactive.
Tracing water flow	Gamma	Radioactive tracers show how water moves through soil and underground systems.

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Choosing the Right Source