Uses of Nuclear Radiation

This lesson covers the practical uses of nuclear radiation as required by the AQA GCSE Physics specification (4.4.2). You need to understand how different types of radiation are used in medicine, industry, and archaeology, and why a particular type of radiation is chosen for each application.

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Choosing the Right Type of Radiation

The type of radiation chosen for a particular application depends on its penetrating power, ionising ability, and half-life. The key principle is:

• The radiation must be able to reach its target (so it needs enough penetrating power).
• The radiation must be detectable or have the desired effect on the target.
• The source must have an appropriate half-life — long enough to be useful, but not so long that it causes lasting contamination.

Radiation	Penetrating Power	Ionising Ability	Typical Uses
Alpha	Very low (stopped by paper)	Very high	Smoke detectors
Beta	Moderate (stopped by aluminium)	Moderate	Thickness monitoring
Gamma	Very high (reduced by lead)	Very low	Medical imaging, sterilisation, cancer treatment

Exam Tip: For every application of nuclear radiation, you should be able to explain WHY that particular type of radiation is used. The answer always relates to the penetrating power, ionising ability, and/or half-life. If a question asks "why is gamma used for...?", your answer must reference the properties of gamma radiation.

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Medical Uses

Medical Tracers (Gamma)

Gamma-emitting isotopes are used as medical tracers to diagnose conditions inside the body without surgery.

How it works:

1. A patient swallows, inhales, or is injected with a radioactive tracer (a gamma-emitting isotope such as technetium-99m).
2. The tracer is absorbed by the organ or tissue being investigated.
3. A gamma camera outside the body detects the gamma rays emitted from inside the body.
4. A computer creates an image showing how the tracer has been distributed, revealing blockages, tumours, or other problems.

Why gamma is used:

• Gamma rays can pass through the body and be detected externally (alpha and beta cannot escape the body).
• Gamma is the least ionising, so it causes the least damage to body cells.

Why technetium-99m is commonly used:

• It has a half-life of 6 hours — long enough for the scan but short enough to minimise radiation exposure.
• It emits only gamma radiation (no alpha or beta), reducing the dose to the patient.

Cancer Treatment — Radiotherapy (Gamma)

Gamma rays from sources such as cobalt-60 are used to treat cancer by directing high-energy beams at tumours.

How it works:

1. Beams of gamma radiation are directed at the tumour from different angles.
2. The beams are focused so they overlap at the tumour site, delivering a high dose to the cancerous tissue.
3. The surrounding healthy tissue receives a lower dose because each individual beam is relatively weak.
4. The radiation damages the DNA of cancer cells, killing them or preventing them from dividing.

Why gamma is used:

• Gamma rays can penetrate deep into the body to reach internal tumours.
• By using multiple beams from different angles, the dose to healthy tissue is minimised.

graph TD
    A["Radiotherapy Treatment"] --> B["Multiple gamma beams<br>from different angles"]
    B --> C["Beams overlap<br>at tumour site"]
    C --> D["High dose to tumour<br>Low dose to healthy tissue"]
    D --> E["Cancer cells killed<br>or prevented from dividing"]

    style A fill:#2c3e50,color:#fff
    style B fill:#9b59b6,color:#fff
    style C fill:#e74c3c,color:#fff
    style D fill:#e67e22,color:#fff
    style E fill:#27ae60,color:#fff

Exam Tip: A common exam question asks you to explain how radiotherapy minimises damage to healthy tissue. The key point is that multiple beams from different angles converge at the tumour, so only the tumour receives the full combined dose. Each individual beam passes through a different area of healthy tissue, spreading the damage and reducing the effect on any single area.

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Industrial Uses

Smoke Detectors (Alpha)

Alpha-emitting isotopes (such as americium-241) are used in smoke detectors.

How it works:

1. The alpha source ionises the air between two electrodes, creating a small, steady electric current.
2. When smoke particles enter the detector, they absorb the alpha particles.
3. The ionisation is reduced, and the current decreases.
4. The drop in current triggers the alarm.

Why alpha is used:

• Alpha particles are strongly ionising, so they ionise the air effectively.
• Alpha particles are stopped by a few cm of air, so they are contained within the detector and do not pose a radiation hazard outside it.

Why americium-241 is used:

• It has a long half-life of 432 years, so the smoke detector will work reliably for many years without needing the source replaced.

Thickness Monitoring in Industry (Beta)

Beta-emitting isotopes are used to monitor the thickness of materials during manufacturing (for example, paper, aluminium foil, or plastic sheets).

How it works:

1. A beta source is placed on one side of the material being produced.
2. A detector is placed on the other side.
3. The amount of beta radiation passing through the material depends on its thickness.
4. If the material is too thick, less radiation reaches the detector, and the rollers are adjusted to make it thinner.
5. If the material is too thin, more radiation reaches the detector, and the rollers are adjusted to make it thicker.

Why beta is used:

• Beta radiation has the right penetrating power — it passes through thin materials like paper and metal sheets but is partially absorbed, so changes in thickness can be detected.
• Alpha would be stopped by even the thinnest material, so no useful signal would reach the detector.
• Gamma would pass through with almost no absorption, so changes in thickness would not be detected.

graph LR
    A["Beta Source"] --> B["Material<br>(paper/metal)"]
    B --> C["Beta Detector"]
    C --> D{"Thickness<br>correct?"}
    D -->|Too thick| E["Rollers adjusted:<br>reduce thickness"]
    D -->|Too thin| F["Rollers adjusted:<br>increase thickness"]
    D -->|Correct| G["No adjustment<br>needed"]

    style A fill:#e74c3c,color:#fff
    style B fill:#f39c12,color:#fff
    style C fill:#2980b9,color:#fff
    style D fill:#2c3e50,color:#fff
    style E fill:#e67e22,color:#fff
    style F fill:#e67e22,color:#fff
    style G fill:#27ae60,color:#fff

Sterilisation of Equipment (Gamma)

Gamma radiation is used to sterilise medical equipment, surgical instruments, and food.

How it works:

• Equipment is sealed in packaging and then exposed to a high dose of gamma radiation.
• The gamma rays kill bacteria and viruses by damaging their DNA.
• The equipment remains sterile inside its sealed packaging.

Why gamma is used:

• Gamma rays are highly penetrating and can pass through the packaging to reach all surfaces.
• The equipment does not become radioactive after irradiation.

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Archaeological and Geological Dating

Carbon Dating (Beta from Carbon-14)

Carbon-14 is a radioactive isotope of carbon with a half-life of 5,730 years. It is used to date organic materials (things that were once alive) up to about 50,000 years old.

How it works:

1. Living organisms absorb carbon-14 from the atmosphere (through food or photosynthesis).
2. While alive, the proportion of carbon-14 to carbon-12 remains constant.
3. When the organism dies, it stops absorbing carbon-14, and the carbon-14 already present begins to decay.
4. By measuring the proportion of carbon-14 remaining in a sample, scientists can calculate how long ago the organism died.

Geological Dating (Uranium-238)

Uranium-238 has a half-life of 4.5 billion years and is used to date very old rocks. By measuring the ratio of uranium-238 to its stable daughter product lead-206, geologists can determine the age of rocks and, by extension, the age of the Earth.

Exam Tip: Carbon dating and uranium dating are based on the same principle (measuring the proportion of a radioactive isotope that has decayed), but they are used for very different timescales. Carbon-14 (half-life 5,730 years) is suitable for dating organic remains up to about 50,000 years old. Uranium-238 (half-life 4.5 billion years) is used for dating rocks that are millions or billions of years old.

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Irradiation vs Contamination

It is important to distinguish between irradiation and contamination: