Uses and hazards of radiation in medicine and industry

What you'll learn

This revision guide covers how different types of ionising radiation are used in medical diagnosis and treatment, as well as industrial applications. You'll learn to evaluate the benefits and risks of radiation exposure, explain why specific radiation types suit particular purposes, and understand the safety precautions necessary when handling radioactive materials.

Key terms and definitions

Ionising radiation — radiation that has enough energy to remove electrons from atoms, creating ions; includes alpha, beta and gamma radiation

Radioactive tracer — a radioactive substance that can be detected outside the body and is used to track the movement of substances through a system

Half-life — the time taken for the activity (or number of undecayed nuclei) of a radioactive source to fall to half its original value

Contamination — unwanted presence of radioactive material on or inside objects or living organisms

Irradiation — exposure to radiation from a source outside the body; does not make the object radioactive

Background radiation — low-level ionising radiation that is present in the environment at all times from natural and artificial sources

Radiotherapy — medical treatment using ionising radiation to destroy cancer cells

Sterilisation — the process of destroying all microorganisms, including bacteria and viruses, on equipment or food

Core concepts

Medical uses of radiation

Diagnostic imaging with tracers

Radioactive tracers are used to investigate the functioning of organs without surgery. A radioactive isotope is introduced into the body (usually by injection or swallowing) and its movement is tracked using external detectors.

Key features of medical tracers:

They must emit gamma radiation or beta-plus particles that can be detected outside the body
They should have a short half-life (hours to days) to minimise radiation exposure after the procedure
The isotope must not be chemically toxic to the patient
It should concentrate in the specific organ being investigated

Technetium-99m is the most commonly used medical tracer because:

It emits only gamma radiation (easily detected, passes through tissue)
Its half-life is 6 hours (long enough for imaging, short enough to limit exposure)
It can be attached to different compounds to target specific organs

Common applications include:

Kidney function tests — tracers show blockages or reduced blood flow
Bone scans — tracers concentrate in areas of damaged or cancerous bone
Thyroid imaging — iodine-131 is absorbed by the thyroid gland

Cancer treatment (radiotherapy)

Radiotherapy uses high doses of ionising radiation to kill cancer cells or prevent them from dividing. The radiation damages the DNA in cancer cells more effectively than healthy cells because cancer cells divide more rapidly.

External radiotherapy:

Beams of gamma rays or X-rays are directed at the tumour from outside the body
Multiple beams from different angles converge on the tumour to maximise dose at the cancer site while minimising damage to surrounding healthy tissue
Cobalt-60 (gamma emitter, half-life 5.3 years) is commonly used

Internal radiotherapy (brachytherapy):

A radioactive source is placed inside or next to the tumour
Beta emitters or alpha emitters can be used because they only need to travel short distances
Iodine-131 (beta emitter, half-life 8 days) treats thyroid cancer

Benefits and risks:

Benefits: Can cure cancer, extend life, reduce symptoms, less invasive than some surgeries
Risks: Damage to healthy cells causing side effects, potential for radiation burns, long-term increased cancer risk from exposure

Industrial uses of radiation

Thickness monitoring in manufacturing

Radiation is used to control the thickness of materials during production of paper, metal foil, and plastic sheets.

How it works:

A beta source is placed on one side of the material
A detector on the opposite side measures how much radiation passes through
If the material is too thick, less radiation reaches the detector
If the material is too thin, more radiation reaches the detector
A computer adjusts the rollers automatically to maintain constant thickness

Why beta radiation is used:

Alpha particles would be completely absorbed even by thin materials (not suitable)
Gamma rays would mostly pass through without enough absorption to detect thickness changes
Beta particles are partially absorbed depending on thickness (ideal for detecting changes)
The source needs a long half-life (years) so it doesn't need frequent replacement

Sterilisation of medical equipment

Gamma radiation is used to sterilise medical instruments, surgical equipment, and food without heating them.

Process:

Items are sealed in packaging
They are exposed to intense gamma radiation from cobalt-60 or caesium-137
Gamma rays kill bacteria, viruses, and fungi by damaging their DNA
Items remain sterile in sealed packaging until opened

Advantages:

Works through packaging (items stay sterile until use)
No heat required (suitable for plastic equipment that would melt)
More reliable than chemical sterilisation
No radioactive residue (irradiation does not make objects radioactive)

Smoke detectors

Household smoke alarms use americium-241, an alpha emitter with a half-life of 432 years.

How it works:

Alpha particles ionise air molecules between two electrodes
This creates a small constant electric current
Smoke particles absorb the alpha particles, reducing the ionisation
The current drops and triggers the alarm

Why alpha radiation is used:

Alpha particles strongly ionise air molecules
They have a short range in air (few centimetres), so don't escape the detector
They are stopped by the outer casing, making the device safe
Long half-life means the detector works for many years

Hazards and safety precautions

Effects of ionising radiation on living cells

Ionising radiation damages living tissue by:

Breaking DNA molecules, causing cell death or mutations
Increasing cancer risk (mutations in genes controlling cell division)
Causing radiation burns at high doses
Damaging developing embryos (pregnant women must avoid exposure)

The risk depends on:

Type of radiation — alpha is most damaging inside the body, gamma least damaging per particle
Dose received — measured in sieverts (Sv); higher dose = greater risk
Duration of exposure — longer exposure increases total dose
Which organs are exposed — some organs (bone marrow, reproductive organs) are more sensitive

Contamination vs. irradiation

Understanding the difference is crucial:

Irradiation:

Exposure to radiation from an external source
Does not make the object radioactive
Stops when you move away from the source
Example: Having an X-ray, gamma sterilisation

Contamination:

Radioactive material gets on or inside objects/people
The contaminated object becomes a radiation source
Continues to emit radiation until the material decays or is removed
Example: Radioactive dust on skin, ingested radioactive material

Safety precautions when handling radioactive materials

To minimise exposure, follow these principles:

Distance:

Use long-handled tongs or robotic arms to handle sources
Store sources in lead-lined containers when not in use
Keep maximum distance from the source

Shielding:

Use appropriate barriers between the source and people
Lead or thick concrete for gamma sources
Aluminium for beta sources
Paper or a few centimetres of air for alpha sources

Time:

Minimise the time spent near radioactive sources
Plan procedures carefully to reduce exposure duration
Work efficiently to complete tasks quickly

Additional precautions:

Never point sources at people
Wear protective clothing and dosimeters (devices that measure radiation dose)
Wash hands thoroughly after handling radioactive materials
Store sources securely with clear warning signs
Monitor for contamination regularly
Dispose of radioactive waste according to regulations

Evaluating uses of radiation

When assessing whether radiation should be used for a particular application, consider:

Benefits:

Medical diagnosis and treatment effectiveness
Lives saved or improved quality of life
Economic benefits (efficiency, automation)
Alternatives available (are they better or worse?)

Risks:

Potential radiation dose to workers and public
Contamination risks
Long-term health effects
Environmental impact of radioactive waste

For medical uses, the benefit usually outweighs the risk when:

The condition being treated is serious or life-threatening
Alternative methods are more dangerous or less effective
Radiation doses are kept as low as reasonably practicable (ALARP principle)

Worked examples

Example 1: Choosing the correct radiation type

Question: A factory manufactures aluminium foil. Explain why a beta source with a long half-life would be suitable for monitoring the thickness of the foil during production. [4 marks]

Answer: Beta particles are partially absorbed by aluminium [1 mark], so changes in thickness will cause detectable changes in the count rate at the detector [1 mark]. Alpha particles would be completely stopped by the foil / gamma rays would mostly pass through without enough absorption [1 mark]. A long half-life ensures the source maintains consistent activity for many years without needing frequent replacement [1 mark].

Mark scheme notes: Award marks for explaining absorption properties, comparing to other radiation types, and justifying the long half-life requirement.

Example 2: Medical tracer properties

Question: Technetium-99m is used as a medical tracer with a half-life of 6 hours. A hospital receives a sample with an activity of 800 MBq at 9:00 am. Calculate the activity of the sample at 9:00 pm the same day. [3 marks]

Answer: Time elapsed = 12 hours [1 mark] Number of half-lives = 12 ÷ 6 = 2 [1 mark] Activity = 800 ÷ 2 ÷ 2 = 200 MBq [1 mark] (Or: 800 × (½)² = 200 MBq)

Alternative acceptable method: After 6 hours (3:00 pm): 800 ÷ 2 = 400 MBq; After 12 hours (9:00 pm): 400 ÷ 2 = 200 MBq

Example 3: Evaluating radiation safety

Question: A student investigates radioactive sources in the laboratory. Describe three safety precautions the student should take and explain why each is important. [6 marks]

Answer: Use tongs to handle the source / keep the source at arm's length [1 mark] to maximise distance from the source, reducing radiation dose [1 mark].

Store the source in a lead-lined box when not in use [1 mark] to absorb radiation and prevent unnecessary exposure to people nearby [1 mark].

Minimise the time spent near the source / plan the experiment before handling sources [1 mark] to reduce the total radiation dose received [1 mark].

Other acceptable precautions: Never point the source at anyone, wear a lab coat/protective clothing, wash hands after use, use appropriate shielding, wear a dosimeter badge.

Common mistakes and how to avoid them

Confusing contamination and irradiation — Remember: irradiation is exposure from outside (like standing in sunlight); contamination is having radioactive material on you (like paint on your clothes). Irradiated objects don't become radioactive.
Choosing the wrong radiation type — Alpha for smoke detectors (strong ionisation, short range); beta for thickness monitoring (partial absorption); gamma for medical tracers and sterilisation (penetrating, detected outside body). Learn the properties and match them to the application.
Forgetting that half-life matters differently for different uses — Medical tracers need short half-lives (hours/days) to minimise patient exposure; industrial sources need long half-lives (years) to avoid frequent replacement; cancer treatment needs moderate half-lives.
Stating that sterilisation makes objects radioactive — Gamma sterilisation is irradiation only. The gamma rays pass through objects, killing microorganisms, but don't make the objects radioactive themselves.
Not explaining why safety precautions work — Don't just list "use tongs" or "use a lead box." Explain that tongs increase distance, reducing intensity; lead absorbs gamma radiation, providing shielding.
Confusing the risks of different radiation types — Alpha is most dangerous inside the body (strongly ionising but short range); gamma is most dangerous outside the body (penetrating but weakly ionising). Match the hazard to the exposure route.

Exam technique for "Uses and hazards of radiation in medicine and industry"

"Explain why" questions require reasons — Don't just state facts. For example, if asked why gamma is used for sterilisation, explain that it penetrates packaging, allowing items to remain sealed and sterile. Link properties to applications.
Compare radiation types explicitly — Questions often ask you to justify why one type is used instead of others. State what's wrong with the alternatives: "Alpha wouldn't work because it would be completely absorbed by the material."
Use correct units and show calculations clearly — Activity is measured in becquerels (Bq) or megabecquerels (MBq). For half-life calculations, show the number of half-lives and work step-by-step. Don't skip steps.
Safety questions reward detail — When describing precautions, use the distance-shielding-time framework. Give specific examples (lead box, tongs, minimise handling time) and explain the physics principle behind each one. Typically worth 1 mark for the precaution, 1 mark for the explanation.

Quick revision summary

Ionising radiation has vital medical uses: gamma-emitting tracers with short half-lives diagnose organ problems; radiotherapy destroys cancer cells. Industrial applications include beta sources for thickness monitoring, gamma rays for sterilisation, and alpha sources in smoke detectors. Each use exploits specific radiation properties (penetration, ionisation, half-life). Key hazards include DNA damage, cancer risk, and contamination. Safety requires minimising exposure through distance, shielding, and time reduction. Always distinguish between irradiation (external exposure, doesn't make objects radioactive) and contamination (radioactive material present on objects).