Uses and Hazards of Radiation

This lesson covers the practical applications of radioactive sources in medicine, industry and everyday life, how the choice of source depends on the type of radiation and half-life, and the hazards associated with radiation. This is part of the AQA GCSE Combined Science Trilogy specification (8464, section 6.4.3).

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Choosing the Right Source

When selecting a radioactive source for a particular application, you must consider:

Factor	Why it matters
Type of radiation (alpha, beta or gamma)	Determines penetrating power and ionising ability — must match the application
Half-life	Must be appropriate — too short and the source decays before it is useful; too long and it poses a prolonged hazard
Activity	The source must emit enough radiation to be detected or have the desired effect

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Medical Uses

Medical Tracers

A radioactive tracer is a substance containing a radioactive isotope that is injected, swallowed or inhaled. It travels through the body and is detected from outside using a gamma camera.

Requirement	Reason
Gamma emitter	Gamma rays penetrate the body and can be detected from outside
Short half-life (hours)	Limits the patient's radiation dose
Not toxic	Must be safe to introduce into the body

Example: Technetium-99m (Tc-99m) — gamma emitter, half-life of 6 hours. Used to image bones, the heart and the thyroid.

Cancer Treatment (Radiotherapy)

• External beam radiotherapy: a focused beam of gamma radiation is directed at a tumour from outside the body. The beam is rotated around the patient so that healthy tissue receives a lower total dose than the tumour.
• The source must have an appropriate activity to deliver the required dose.

Sterilisation of Medical Equipment

• Gamma radiation penetrates sealed packaging and kills bacteria on surgical instruments.
• The instruments do not become radioactive — they are irradiated, not contaminated.

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Industrial Uses

Thickness Monitoring

Radioactive sources are used to monitor and control the thickness of materials in manufacturing (e.g. paper, aluminium foil, steel sheets).

Material being monitored	Radiation used	Why?
Paper	Beta	Beta is partially absorbed by paper — changes in thickness change the count rate reaching the detector
Metal sheets	Gamma	Gamma can penetrate metal — changes in thickness change the amount transmitted

graph LR
    S["Radioactive<br/>source"] --> M["Material<br/>(paper/metal)"]
    M --> D["Detector"]
    D --> C["Controller adjusts<br/>rollers if thickness<br/>is wrong"]

• If the material is too thick, less radiation reaches the detector → the machine adjusts the rollers to make the material thinner.
• If the material is too thin, more radiation reaches the detector → the machine adjusts accordingly.

Exam Tip: Alpha radiation would not be suitable for thickness monitoring because it is stopped by a few centimetres of air — it would never reach the detector.

Leak Detection in Pipes

• A gamma-emitting tracer is added to the fluid in a pipe.
• A detector above ground detects increased radiation at the point where the pipe is leaking.
• The tracer must have a short half-life so it does not remain in the environment.

Smoke Detectors

• Contain a small amount of americium-241 (an alpha emitter with a long half-life of ~432 years).
• Alpha particles ionise the air between two electrodes, allowing a small current to flow.
• When smoke enters, it absorbs the alpha particles, reducing the ionisation and the current — this triggers the alarm.

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Other Uses

Carbon Dating

• Carbon-14 is a beta emitter with a half-life of approximately 5730 years.
• Living organisms continuously take in carbon (including a small proportion of C-14). When they die, they stop absorbing carbon and the C-14 decays.
• By measuring the ratio of C-14 to stable C-12 in a sample, scientists can estimate the age of once-living material (up to about 50 000 years old).

Food Irradiation

• Gamma radiation is used to irradiate food, killing bacteria and extending shelf life.
• The food does not become radioactive — it is irradiated, not contaminated.

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Hazards of Radiation

Radiation can damage living cells in two ways:

Effect	Description
Cell death	High doses of radiation kill cells outright — this can cause radiation sickness (nausea, burns, organ failure)
DNA mutation	Lower doses can damage DNA, potentially causing mutations that may lead to cancer

Risk Assessment

The risk from radiation depends on:

• The type of radiation (alpha is most ionising inside the body)
• The dose (amount of radiation received)
• The duration of exposure
• Whether the source is external (irradiation) or internal (contamination)

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Comparing Alpha, Beta and Gamma Hazards

Scenario	Most dangerous type	Why?
Source outside the body	Gamma	Most penetrating — can pass through skin and reach internal organs
Source inside the body (inhaled, ingested)	Alpha	Most ionising — causes the most damage to nearby cells and tissue

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Risk vs Benefit

In many applications, the benefits of using radiation outweigh the risks, provided safety precautions are followed:

Application	Benefit	Risk	How risk is minimised
Medical tracers	Accurate diagnosis of disease	Small radiation dose to patient	Use short half-life sources; keep dose as low as possible
Radiotherapy	Can cure or reduce cancer	Damage to healthy tissue	Focus beams on tumour; rotate around patient; shield healthy tissue
Smoke detectors	Save lives by detecting fires	Tiny amount of radioactive material in the home	Sealed source; alpha particles cannot penetrate the casing
Thickness monitoring	Consistent product quality	Workers exposed to radiation	Shielding; distance; dosimeters for workers

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Common Misconceptions

Misconception	Correction
All radiation causes cancer	The risk depends on the dose and type — very low doses (like background radiation) pose negligible risk
Food irradiated with gamma becomes radioactive	No — irradiation does not make the food radioactive; it kills bacteria
Any radioactive source can be used for any application	The type of radiation and half-life must be carefully matched to the application
Nuclear radiation is the same as electromagnetic radiation	Alpha and beta are particles; only gamma is part of the electromagnetic spectrum
Radiation only comes from nuclear power stations	The largest source of radiation for most people is radon gas from rocks

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Summary

• Radioactive sources are chosen based on their type of radiation, half-life and activity.
• Medical uses: tracers (gamma, short half-life), radiotherapy (gamma), sterilisation (gamma).
• Industrial uses: thickness monitoring (beta for paper, gamma for metal), leak detection (gamma), smoke detectors (alpha, long half-life).
• Other uses: carbon dating (beta from C-14), food irradiation (gamma).
• Radiation can cause cell death or DNA mutations leading to cancer.
• Gamma is most dangerous externally; alpha is most dangerous internally.
• The benefits of using radiation often outweigh the risks when proper safety precautions are followed.

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Worked Example 1 — Choosing a Medical Tracer

A doctor needs a tracer to image the thyroid. Which of the following isotopes is most suitable, and why?

Isotope	Radiation	Half-life
A: Americium-241	Alpha	432 years
B: Strontium-90	Beta	29 years
C: Technetium-99m	Gamma	6 hours
D: Uranium-238	Alpha	4.5 billion years

Answer: C — Technetium-99m.