Using Radioisotopes — Medicine, Industry and the Environment
The same instability that makes a nucleus dangerous also makes it useful. Around 40 million nuclear-medicine procedures happen worldwide every year — and Australia helps supply them.
Q1 · Radioisotopes give off radiation that can be detected from outside the body, and that radiation can also damage cells. List one way each of these properties could be useful in medicine.
Q2 · If you were a doctor choosing a radioisotope to put inside a patient, would you want one with a very long half-life or a short one? Why?
● Know
- How radioisotopes are used in medicine (diagnosis and treatment)
- How radioisotopes are used in industry (tracers, gauges, sterilisation)
- How radioisotopes are used in environmental monitoring (tracing pollution, dating, erosion)
● Understand
- Why the choice of isotope depends on its half-life and type of radiation
- That benefits must be weighed against radiation risks to patients, workers and the public
- How safety practices reduce risk so the benefits can be realised
● Can do
- Match a radioisotope use to medicine, industry or the environment
- Evaluate the benefits and considerations of a given radioisotope application
- Make and justify an evidence-based judgement about a use of radioisotopes
Nuclear medicine uses radioisotopes in two main ways.
Diagnosis (seeing inside the body). A small amount of a radioisotope — a tracer — is given to the patient. Because it emits radiation that passes out of the body, a special camera can detect where it goes and build an image. Technetium-99m is the most widely used; it is a gamma emitter with a short 6-hour half-life, so it images organs clearly and then quickly decays away, keeping the patient's dose low. PET scans use other tracers to find tumours.
Treatment (destroying harmful cells). Radiation can kill cells, which is harmful in general but useful when aimed at cancer. In radiotherapy, beams of gamma radiation (often from cobalt-60) are focused on a tumour to destroy cancer cells while sparing healthy tissue as much as possible. Iodine-131 is swallowed to treat an overactive thyroid: because the thyroid naturally absorbs iodine, the radioisotope concentrates there and its radiation destroys the overactive tissue.
Choosing the right isotope is a balance: it must give off the right kind of radiation for the job and have a half-life long enough to work but short enough to limit the dose.
A patient with a suspected bone problem is given a technetium-99m tracer that collects in active bone. A gamma camera then shows "hot spots" where the bone is most active, revealing fractures or disease that an X-ray might miss. Because Tc-99m has only a 6-hour half-life, the patient is barely radioactive by the next day.
Australia supplies the world: ANSTO's OPAL reactor at Lucas Heights is one of the world's major producers of molybdenum-99, the parent isotope used to make technetium-99m. Australian-made medical isotopes are exported to dozens of countries, supporting millions of scans every year. This is a direct, life-saving benefit of nuclear science.
A diagnostic tracer is not the same as a treatment. Tracers use tiny amounts of radiation just to be seen; therapy uses larger, targeted doses to destroy cells. Confusing the two leads to wrong reasoning about dose and risk.
Industry. Radioisotopes are remarkably useful tools:
- Tracers follow the flow of liquids or gases. Adding a radioactive tracer to an underground pipeline lets engineers detect a leak by where radiation escapes — without digging up the whole pipe.
- Thickness and level gauges use the fact that more material absorbs more radiation. A detector reads how much radiation passes through paper, metal or plastic, letting a factory control thickness automatically.
- Sterilisation: gamma radiation (often from cobalt-60) kills bacteria on medical equipment, syringes and even some foods, without heat.
Environmental monitoring. Radioisotopes help scientists understand and protect the natural world:
- Tracing pollution and water: tracers track how pollutants spread through rivers and groundwater, or how water moves through soil and aquifers.
- Measuring erosion: naturally occurring isotopes such as caesium-137 are used to measure how fast soil is being lost from farmland.
- Dating: the half-life dating you met in Lesson 24 lets scientists work out the age of sediments, ice and once-living material to reconstruct past environments.
A water utility suspects a buried pipe is leaking. Engineers add a short-lived radioactive tracer to the water and walk the line with a detector. Where the radiation reading spikes in the soil, that is where the water — and therefore the leak — is escaping. The tracer's short half-life means it soon decays to safe levels.
Caring for Australian land and water: CSIRO and Australian universities use radioisotope tracers to study soil erosion on farms, the movement of groundwater in the Great Artesian Basin and the spread of nutrients on the Great Barrier Reef. This information guides land management decisions that protect both food production and fragile ecosystems — combining nuclear science with environmental care, including alongside Indigenous land-management knowledge.
Sterilising or irradiating food with gamma radiation does not make the food radioactive. Gamma rays pass through, killing microbes, but they do not leave radioactive atoms behind. Confusing "exposed to radiation" with "becomes radioactive" is a very common error.
Quick-fire true or false on uses of radioisotopes.
Technetium-99m is widely used as a medical tracer.
Gamma radiation can sterilise medical equipment.
Food irradiated with gamma rays becomes radioactive.
A radioactive tracer can locate a leak in a buried pipe.
Radiotherapy uses radiation to destroy cancer cells.
The choice of isotope does not depend on its half-life.
Radioisotopes can trace pollution in rivers and groundwater.
Using radioisotopes involves weighing benefits against radiation risks.
To evaluate a use of radioisotopes — the verb the syllabus asks for — you weigh the benefits against the considerations and reach a justified judgement.
Benefits include: saving lives through diagnosis and cancer treatment; detecting problems (leaks, disease) without invasive or destructive methods; sterilising equipment to prevent infection; protecting the environment by tracing pollution and erosion.
Considerations and risks include: radiation can damage healthy cells and increase cancer risk if doses are too high; workers producing and handling isotopes need protection; radioactive waste must be stored safely until it decays; and there are ethical and public-trust issues about consent and safety.
How risk is managed: doctors use the smallest effective dose; short-half-life isotopes are chosen so radiation soon disappears; shielding, distance and time limits protect workers; and radioactive materials are tracked and regulated. A good evaluation does not just list good and bad points — it weighs them and concludes whether, on balance, the benefit justifies the risk for that specific use.
Evaluating a bone scan: Benefit — it can reveal cancer or fractures early, allowing life-saving treatment. Consideration — it exposes the patient to a small dose of radiation. Judgement — because the dose is very small (less than many other medical tests) and the diagnostic benefit can be life-saving, the benefit clearly justifies the risk. The short-half-life tracer further reduces the dose. On balance, the scan is justified.
Regulation in Australia: The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) sets strict national standards for how radioisotopes are used in hospitals, industry and research. These rules ensure that doses to patients, workers and the public are kept "as low as reasonably achievable" — a real-world example of formally weighing benefit against risk.
"Radiation is always bad, so radioisotopes should never be used." This is not a balanced evaluation. A genuine evaluation weighs the very real life-saving and environmental benefits against the managed risks, rather than rejecting (or accepting) the technology outright.
Connect the key ideas about using radioisotopes. Click two connected ideas to explain the link.
Wrong: "Food treated with gamma radiation is dangerous because it becomes radioactive." No — irradiation kills microbes but leaves no radioactive atoms in the food. The food is not radioactive.
Right: Gamma irradiation passes through food and kills bacteria without making the food radioactive, which is why it can be used to preserve some foods and sterilise equipment.
Wrong: "Any radioisotope will do for a medical tracer." No — the isotope must emit detectable radiation (usually gamma) and have a half-life short enough to limit the patient's dose. The choice is carefully matched to the job.
Right: The type of radiation and the half-life must be matched to the application, balancing usefulness against the dose to the patient or worker.
Wrong: "Evaluating means just listing some good points and some bad points." No — to evaluate, you must weigh them against each other and reach a justified overall judgement for the specific case.
Right: A proper evaluation weighs benefits against considerations and concludes whether, on balance, the use is justified, supported by reasons.
A Nuclear-Medicine Powerhouse Without Nuclear Power
Australia has no nuclear power stations, yet it is one of the most important nuclear-medicine nations on Earth. ANSTO's reactor at Lucas Heights produces medical isotopes used in hundreds of thousands of Australian procedures each year and exports them around the world. Australian hospitals run PET and gamma-camera scans daily, and Australian researchers use radioisotopes to study everything from coral reefs to outback groundwater.
All of this is governed by ARPANSA's strict safety standards, which formally weigh benefit against risk — the very skill this lesson develops. It shows that with careful management, the instability of the nucleus can be turned into one of society's most powerful tools for health and environmental care.
✍ Copy Into Your Books
▾Medicine
- Diagnosis: tracers (e.g. Tc-99m) emit detectable radiation → images
- Treatment: radiotherapy (Co-60) and I-131 destroy harmful cells
- Choose isotope by radiation type + half-life (low dose)
Industry & Environment
- Tracers find pipe leaks; gauges measure thickness
- Gamma sterilises equipment (food not made radioactive)
- Trace pollution/groundwater; measure erosion; date sediments
Evaluating
- Benefits: save lives, detect problems, protect environment
- Considerations: cell damage, waste, worker safety, ethics
- Manage risk: low dose, short half-life, shielding, regulation
- Evaluate = weigh both and judge if justified
Match the Use
Make a Judgement
At the start, the hook asked how deliberately using radioactive atoms can be a good thing, and where the line is between benefit and risk.
Now write a balanced answer: give one clear benefit and one clear consideration, and explain how the risk is managed so the benefit can be safely realised. Revisit your Q2 answer about half-life — was your reasoning correct?
Q1. Describe one use of a radioisotope in medicine and one use in environmental monitoring. For each, name the benefit to society. (3 marks)
Q2. Explain why the half-life and type of radiation of an isotope must be considered when choosing it for a medical tracer. Use technetium-99m as an example. (4 marks)
Q3. Evaluate the use of radioisotopes for treating cancer. Weigh at least one benefit against at least one consideration, and give a justified overall judgement. (3 marks)
Revisit Your Thinking
Go back to your Think First answers. Has your understanding changed?
- Can you now give a use that relies on detecting radiation, and one that relies on radiation damaging cells?
- Was your reasoning about choosing a short or long half-life correct?
Model answers (click to reveal)
Answers
▾MCQ 1
C — A medical tracer is given so that the radiation it emits can be detected from outside the body and used to build an image of an organ or process.
MCQ 2
B — Using a tracer to find a leak in a buried pipeline is an industrial application. The others are medical or environmental.
MCQ 3
D — Gamma rays kill bacteria without heat and pass straight through; they do not leave radioactive atoms behind, so the equipment is not made radioactive.
MCQ 4
A — A short half-life means the radioisotope decays away soon after the scan, so the patient receives only a small total radiation dose.
MCQ 5
C — A balanced evaluation weighs benefits against managed risks and concludes that, for each specific use, the life-saving benefit usually justifies the small, carefully controlled risk. The other options ignore one side entirely.
Short Answer 1
Model answer: Medicine: technetium-99m is injected as a tracer so a gamma camera can image an organ such as bone or the heart; the benefit is early, accurate diagnosis of disease, allowing timely treatment. Environmental monitoring: a radioisotope tracer is added to groundwater to track how it moves through an aquifer; the benefit is better management and protection of water resources such as the Great Artesian Basin.
Short Answer 2
Model answer: The half-life matters because the isotope must last long enough to complete the scan but then decay quickly so the patient's total radiation dose stays low. The type of radiation matters because the radiation must be able to pass out of the body to reach the camera — gamma radiation does this well, whereas alpha particles would be absorbed in the body and only add to the dose. Technetium-99m is chosen because it is a gamma emitter with a roughly 6-hour half-life: it images clearly and then decays away rapidly, an ideal combination.
Short Answer 3
Model answer: A clear benefit of using radioisotopes in cancer treatment is that targeted radiation can destroy cancer cells and save lives where other treatments may fail. A key consideration is that the radiation can also damage nearby healthy tissue and the patient is exposed to a dose that carries some risk. However, doses are carefully targeted and controlled, and treatment is only used when the cancer poses a greater threat than the radiation. On balance, because the life-saving benefit is large and the risk is managed and justified by the patient's condition, the use of radioisotopes in cancer treatment is justified.