Ch 8 · 5.2.6 Safety Precautions · O Level Physics 5054
Topic 8 of 8 in Nuclear Physics — O Level Physics 5054 — 39 lessons.
Introduction
Radioactive sources save lives in hospitals and are used safely every day in industry and schools. The key is to understand how radiation harms the body, and the three simple ways to reduce the dose. (Syllabus section 5.2.6.)
Key ideas — How ionising radiation harms living things
Alpha, beta and gamma radiation are ionising: they knock electrons off atoms and molecules in the cells they pass through. This can:
🧑🏫 Teacher's explanation
Imagine a crowded hallway where people are walking through. If someone starts throwing heavy, jagged rocks (ionising radiation) through the crowd, they will likely hit people. If the rocks are small and light, they might just bump someone; if they are massive and heavy, they might knock someone down completely or break something they are carrying. In your body, those 'people' are your cells and the 'items they are carrying' is your DNA.
📖 Definitions
🔍 Worked example — Easy
A technician is working near a beta source. To reduce the dose received, they decide to move from a distance of 0.5 m to 1.5 m. Explain why this is a valid safety precaution.
🔍 Worked example — Standard
A scientist is handling an alpha emitter. Why is the primary risk associated with this source if it is accidentally inhaled, rather than just being held near the skin?
🔍 Worked example — Exam-style
A hospital uses a gamma source for imaging. To ensure safety, the source is kept inside a thick lead container. Identify the safety principle used and explain why it works.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State one way the scientists can reduce the dose of radiation received by the person using the source. [1] (b) Explain why gamma radiation is more dangerous to living tissue than alpha radiation when the source is placed outside the body. [2] [3 marks]
Key ideas — Reducing the dose
(a) Reduce exposure time. The less time spent near a source, the smaller the dose. Work quickly; do not leave sources out longer than needed.
🧑🏫 Teacher's explanation
Think of radiation like a spray of paint from a nozzle. If you stand right next to it for a long time, you will get covered in paint. If you stand far away, the spray spreads out and hits you much less. If you put a piece of cardboard between you and the nozzle, you won't get any paint on you at all. This is exactly how we manage radiation safety.
📖 Definitions
🔍 Worked example — Easy
A technician works near a beta source. If they reduce their exposure time from 60 s to 15 s, by what factor is the radiation dose reduced?
🔍 Worked example — Standard
A worker is standing 2.0 m from a gamma source. If they move to a distance of 6.0 m, how does the radiation dose change? (Assume the dose follows the inverse square law I ∝ 1/d^2)
🔍 Worked example — Exam-style
A scientist is handling a source that emits both alpha and gamma radiation. Suggest the most appropriate shielding for each type and explain why a lead apron is used.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Moving, using and storing sources
🧑🏫 Teacher's explanation
Imagine you are standing near a loud speaker playing heavy metal music. If you stand right next to it for hours, you might damage your hearing. If you stand far away, or only listen for a few seconds, the risk of damage is much lower. Ionising radiation works similarly; it carries enough energy to knock electrons off atoms, which can damage the biological 'blueprints' inside your cells.
📖 Definitions
🔍 Worked example — Easy
A technician needs to move a radioactive source. List three safety precautions they should take to minimize exposure.
🔍 Worked example — Standard
A scientist is using a radioactive source for an experiment. They decide to move the source from 2.0 m to 4.0 m away from their body. How does this affect their safety?
🔍 Worked example — Exam-style
A student is asked to explain why eating near a radioactive source is dangerous and how to prevent it.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State two biological effects of ionising radiation on living tissue. [2] (b) Explain how the following three methods reduce the radiation dose received by a technician: (i) Using lead-lined containers. [1] (ii) Using long-handled tongs. [1] (iii) Minimizing the time spent near the source. [1] [5 marks]
Worked example
A teacher demonstrates a gamma source. State three precautions and explain how each reduces the risk.
🔍 Worked example — Easy
A technician is working with a gamma source. They decide to use long-handled tongs instead of their hands. Explain how this reduces the risk of radiation exposure.
🔍 Worked example — Standard
A laboratory stores a radioactive sample in a thick lead-lined container. Why is this container effective at protecting the user?
🔍 Worked example — Exam-style
A student is performing an experiment involving a radioactive source. They notice that the dose received increases significantly if they stay near the source for 10 minutes compared to 10 seconds. State the safety precaution being applied here and explain its effect.
⚠️ Common errors
Common mistakes
Practice
Answers: (1) Cell death; mutations; cancer. (2) Reduce the exposure time; increase the distance from the source; use shielding. (3) Lead absorbs radiation (including much of the gamma radiation), shielding people nearby. (4) Outside, alpha is stopped by the dead outer layer of skin; inside, it is absorbed by living cells nearby and, being strongly ionising, causes a lot of damage.