Radiation Safety & Uses

IGCSE Edexcel Physics
7.9–7.16 Background radiation, detectors, hazards, safety precautions and uses
Key Concepts: Background radiation is always present from natural and artificial sources. Ionising radiation can damage DNA and cause cancer. Safety precautions: distance, shielding and limiting exposure time. Radiation is used in medicine (tracers, radiotherapy), industry (thickness gauges, sterilisation) and archaeology (carbon dating).

Section A — Background Radiation

1. Define background radiation. [2]
2. List three natural sources and two artificial sources of background radiation. [3]
3. Explain why background radiation must be measured and subtracted when investigating a radioactive source. [2]

Section B — Detecting Radiation

4. Name two instruments used to detect ionising radiation and describe how each works. [4]

Section C — Hazards and Safety

5. Explain two ways ionising radiation can damage living cells. [4]
6. State three safety precautions that should be taken when handling radioactive sources in a laboratory. [3]
7. Explain how each precaution in question 6 reduces the risk of harm. [3]
8. Describe the difference between contamination and irradiation by a radioactive source. [2]

Section D — Uses of Radioactivity

9. Describe how a radioactive tracer is used to detect a blockage in a pipe. [3]
10. Explain why a gamma source is used as a medical tracer rather than an alpha source. [2]
11. Describe how radioactive carbon dating is used to estimate the age of a once-living object. [3]

Total marks: 31

Mark Scheme

1. Background radiation is low-level ionising radiation that is always present in the environment [1]; it comes from both natural and artificial sources [1] [2]
2. Natural (any three): radon gas from rocks, cosmic rays, food/drink, rocks/soil, living organisms [2]; Artificial (any two): medical X-rays/radiotherapy, nuclear power stations, nuclear weapons testing [1] [3]
3. Background radiation would be counted along with radiation from the source [1]; subtracting it gives the true count rate from the source alone [1] [2]
4. Geiger-Muller (GM) tube: ionising radiation enters the tube and ionises the gas inside, causing a pulse of current which is counted [2]; Film badge: radiation exposes photographic film and the degree of darkening shows total dose received [2] [4]
5. Ionising radiation can ionise molecules in cells [1]; this can damage or break DNA strands, causing mutations [1]; high doses can kill cells directly [1]; mutations can lead to cancer [1] (award any 4) [4]
6. Any three: keep distance from the source (handle with tongs) [1]; limit time of exposure [1]; use shielding (lead apron / lead container) [1]; never point source at people; store in lead-lined box [3]
7. Distance: intensity of radiation decreases with distance, reducing dose [1]; time: less time = less total radiation absorbed [1]; shielding: absorbs radiation before it reaches the body [1] [3]
8. Irradiation is exposure to radiation from an external source — the person is not radioactive themselves [1]; contamination is when radioactive material gets on or inside the body, continuing to irradiate tissues [1] [2]
9. A gamma-emitting tracer is injected into (or added to) the pipe [1]; a detector is moved along the pipe to measure count rate [1]; where count rate drops suddenly, there is a blockage preventing the tracer from passing [1] [3]
10. Gamma radiation can penetrate the body to be detected externally [1]; alpha radiation would be stopped by body tissue and could not be detected, and would also cause more internal damage [1] [2]
11. Living organisms absorb carbon-14 throughout their lives [1]; when they die, C-14 is no longer absorbed and begins to decay [1]; by measuring the current C-14 activity and comparing it to the known starting activity, the age can be calculated using the half-life of C-14 (5730 years) [1] [3]