How is radiation used safely, and what are its hazards?
The uses of radioactive sources (medical tracers, treating cancer, sterilisation, smoke alarms and thickness control), the difference between irradiation and contamination, the hazards of ionising radiation, and how exposure is reduced.
A focused answer to OCR Gateway GCSE Physics A topic P6 on the uses and hazards of radiation, covering medical tracers, radiotherapy, sterilisation, smoke alarms and thickness control, the difference between irradiation and contamination, the hazards of ionising radiation, and how exposure is reduced.
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What this topic is asking
OCR wants you to describe the uses of radioactive sources, explain the difference between irradiation and contamination, describe the hazards of ionising radiation, and explain how exposure to radiation is reduced. This is topic P6.2 of the OCR Gateway Physics A (J249) specification.
Uses of radioactive sources
The key idea is that the penetration of the radiation must match the task: alpha for the air gap in a smoke alarm, beta for thin sheets, and gamma where the radiation must pass through the body or packaging.
Irradiation and contamination
Contamination is often more dangerous over time because the source stays with the person and keeps emitting radiation, especially if an alpha source is breathed in or swallowed, since alpha is highly ionising once inside the body where there is no skin to stop it.
Hazards of ionising radiation
Different radiations are dangerous in different ways: outside the body, gamma and beta are the main hazard because they penetrate the skin, while alpha is stopped by skin or clothing. Inside the body, alpha becomes the most dangerous because it is the most ionising and deposits all its energy in nearby tissue.
Reducing exposure
The three standard ways to reduce exposure to an external source are: shielding (using lead or concrete to absorb the radiation), increasing the distance from the source (intensity falls with distance), and limiting the time of exposure. People who work with radiation wear dosimeter badges to monitor their cumulative dose. To reduce contamination, workers wear protective clothing and gloves, handle sources with tongs, use sealed sources or fume cupboards, and avoid eating, drinking or breathing near sources.
Try this
Q1. State the three ways to reduce exposure to radiation from an external source. [3 marks]
- Cue. Shielding (lead or concrete), increasing the distance, and limiting the time of exposure.
Q2. State why an alpha source is used in a smoke alarm rather than a gamma source. [1 mark]
- Cue. Alpha ionises the air and is absorbed by smoke (changing the current); gamma would pass straight through and not be affected by smoke.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksExplain the difference between irradiation and contamination, and state one way to reduce the risk from each.Show worked answer →
A P6 question worth four marks. Irradiation is being exposed to radiation from an outside source; the object or person is not made radioactive, and the risk ends when the source is removed or shielded (1 mark). Contamination is getting radioactive material onto or into an object or the body (for example, swallowing or breathing it in); the contaminated object now emits radiation itself until the material is removed or decays (1 mark). To reduce irradiation, shield the source (lead), increase the distance, or limit the time of exposure (1 mark). To reduce contamination, wear protective clothing and gloves, use a fume cupboard or sealed source, and avoid eating or breathing near sources (1 mark). Markers reward the external-versus-internal distinction and a valid precaution for each.
OCR 20214 marksA radioactive tracer is used to find a blockage in a patient's kidney. Explain why a gamma-emitting source with a short half-life is chosen for this medical use.Show worked answer →
A P6 question worth four marks applying source properties to a use. A gamma emitter is chosen because gamma radiation is penetrating, so it can pass out of the body to be detected outside by a camera (2 marks for gamma being penetrating and detectable outside). A short half-life is chosen so that the source decays away quickly, limiting the patient's exposure to ionising radiation, but is long enough to complete the scan (2 marks for the short half-life reducing exposure). Markers reward gamma being penetrating and detectable, and the short half-life limiting the dose. A common error is to choose alpha (which would be absorbed inside the body and not detected).
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