Uses and risks of radiationIB MYP Physics: Revision notes
Section 1
Medical uses
- Imaging with tracers: a gamma-emitting tracer with a short half-life is injected or swallowed. A camera outside the body detects the gamma rays to show how organs are working.
- Radiotherapy: a beam of gamma rays is aimed at a tumour from several directions. The tumour receives a high dose, while healthy tissue along each beam receives a lower dose. The radiation kills cancer cells.
- Sterilising equipment: gamma rays kill microbes on sealed surgical instruments and syringes, without the heat that could damage plastic.
Section 2
Industrial uses
- Thickness gauging: a beta source on one side of a sheet of paper, plastic or metal foil and a detector on the other side. A thicker sheet absorbs more radiation, so the count rate falls, and the rollers are adjusted. Alpha would be stopped and gamma would pass straight through.
- Leak detection: a gamma-emitting tracer is added to the liquid or gas in a pipe. A detector above ground finds the point where the count rate is high, showing where the tracer has leaked into the soil.
Section 3
Food irradiation and dating
Food irradiation: food is passed by a gamma source. The radiation ionises molecules in bacteria and mould, killing them, so the food lasts longer and is safer. The food does not become radioactive.
Dating: the decay of isotopes such as carbon-14 is used to find the age of once-living material.
Irradiated food is not radioactive. The radiation passes through it and does not stay in it.
Section 4
Harmful effects of radiation
Ionising radiation removes electrons from atoms, which damages molecules in cells.
- Damage to DNA can kill cells or cause them to divide out of control, which may lead to cancer.
- A high dose can cause radiation sickness, burns and hair loss.
- Alpha sources are most harmful if swallowed or breathed in, because they ionise strongly inside the body. Gamma and beta sources are more of a danger from outside the body.
The risk depends on the dose: the amount of radiation absorbed.
Section 5
Safety precautions and monitoring
To reduce the dose:
- Shielding: keep sources in lead containers and use concrete or lead barriers.
- Distance: stay as far from a source as possible, and handle sources with tongs.
- Time: spend as little time as possible near a source.
People who work with radiation wear a film badge. The film darkens when it is exposed to radiation. It is developed regularly to show the total dose, so that the employer can check it is below the safe limit.
Remember the three precautions as shielding, distance and time.
Must Know
- Medical: tracers and imaging, radiotherapy, sterilising equipment.
- Industrial: thickness gauging (beta) and leak detection (tracer).
- Food irradiation kills microbes; the food does not become radioactive.
- Ionisation damages cells, DNA and may cause cancer.
- Reduce dose with shielding, distance and time; film badges monitor dose.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Uses and risks of radiation
- A hospital in Cape Town treats a patient who has a tumour using a beam of gamma rays. The beam is aimed at the tumour from several different directions around the patient's body.Explain why gamma rays can kill cancer cells.2 marks
- A paper mill in Finland makes a continuous sheet of paper that must have a constant thickness. A radioactive source on one side of the moving sheet sends radiation through the paper to a detector on the other side. A computer monitors the count rate at the detector and adjusts the rollers that press the paper.Explain why a source with a long half-life is chosen for this job.2 marks
- A hospital radiographer works with a gamma source for several hours each day. She follows three safety rules: she keeps the source in a lead container when it is not in use, she stays as far from the source as she can, and she limits the time she spends near it. She also wears a film badge.Explain how each of her three rules reduces the radiation dose she receives.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).