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Pearson Edexcel PhysicsAtomic structure

Uses and risks of radiation

Choose suitable radiation for medical and industrial uses.

Start here

The key idea

The most suitable radiation depends on penetration, ionisation and half-life.

Uses And Risks Of Radiation
smokealphathicknessbetatracergammalimit exposure: time, distance, shielding

Use the labels to explain the scientific relationship shown.

Revision notes

The bit that matters

Short notes first. Learn the idea, then use the worked example and questions to check it properly.

1

Background radiation

Background radiation is the low-level ionising radiation that is around us all the time.Its main natural sources are radon gas from rocks, cosmic rays from space, and radioactive substances in rocks, soil, food and our bodies.Human-made sources, such as medical X-rays and nuclear waste, add a smaller amount.Background levels vary with location, for example being higher in areas with granite rock.

2

Dangers of radiation

Ionising radiation can damage living cells.Irradiation means being exposed to radiation from an outside source, while contamination means getting radioactive atoms onto or into the body.Contamination is often more dangerous because the source keeps emitting radiation inside the body.Radiation can kill cells or damage their DNA, which may cause mutations and lead to cancer.Radiation dose, in sieverts (Sv), measures the risk of harm.

3

Medical uses

Radiation is used in medicine despite the risks because the benefits can outweigh the harm.Gamma-emitting tracers are injected and followed with a detector to study organs such as the kidneys.Gamma rays from outside the body, or beta tracers, can be used in imaging and diagnosis.High-energy gamma radiation is used in radiotherapy to kill cancer cells, with beams carefully aimed to limit damage to healthy tissue.

4

Other uses and protection

Beta sources are used in thickness monitoring of paper or foil, since the amount of radiation passing through depends on the thickness.Gamma is used to sterilise medical equipment and to check for cracks in metals.Workers reduce their exposure by keeping their distance, limiting time near sources, wearing protective clothing or using lead and concrete shielding, and storing sources safely in lead-lined containers.

Key terms

Definitions to learn

Background radiation

Low-level ionising radiation present in the environment at all times.

Irradiation

Being exposed to radiation from an external source.

Contamination

Getting radioactive atoms onto or inside an object or body.

Radiation dose

A measure of the risk of harm from radiation, in sieverts (Sv).

Radiotherapy

Using high-energy radiation to kill cancer cells.

Worked example

Explain why gamma radiation is suitable as a medical tracer outside the body.

1

Consider penetration.

2

Consider detection.

Final answer

Gamma radiation can pass out of the body and be detected externally.

Exam habit

Justify radiation choices by linking penetrating power to the use.Medical tracers need gamma (passes out of the body); sterilisation needs gamma (high energy); thickness monitoring needs beta (partially absorbed).Name the type and give the reason.

Watch out

Do not suggest alpha radiation for a tracer that must be detected outside the body.

Examiner tips

How to score full marks

  • 1Distinguish irradiation (external exposure) from contamination (radioactive atoms on or in you).
  • 2Justify medical uses by saying the benefit to the patient outweighs the small risk.
  • 3Protection methods: increase distance, reduce time, and use shielding such as lead.
Practice questions

Try these yourself

Start with the core skill, then open the answer only after you have attempted the full question.

1Why is a short half-life useful for a medical tracer?
Mark scheme
  1. 1.Balance detection with patient dose.
It lasts long enough for the test but reduces the patient's exposure afterwards.
2Explain how radiation can cause cancer.
Mark scheme
  1. 1.Link ionisation to cells and DNA.
Ionisation can damage DNA, causing mutations that may lead to uncontrolled cell division.
3Choose a suitable source for thickness monitoring of paper and explain your choice.
Mark scheme
  1. 1.The radiation must pass partly through the paper.
Beta radiation is suitable because some is absorbed and some passes through, so thickness changes alter the detector reading.
4Name two natural sources of background radiation.[2 marks]
Mark scheme
  1. 1.Recall everyday natural sources.
Any two of: radon gas, cosmic rays, rocks/soil, food and drink (1 each, max 2)
5Explain the difference between irradiation and contamination.[2 marks]
Mark scheme
  1. 1.Define each term clearly.
Irradiation is being exposed to radiation from an external source (1); contamination is having radioactive atoms on or inside the body or an object (1)
6Explain why a gamma emitter, rather than an alpha emitter, is used as a medical tracer inside the body.[2 marks]
Mark scheme
  1. 1.Consider which radiation can leave the body.
  2. 2.Consider ionising damage to tissue.
Gamma is highly penetrating so it can pass out of the body to be detected (1); it is weakly ionising so it causes less damage to internal tissue than alpha, which would be strongly ionising and would not escape to be detected (1)
7Describe two ways a worker who handles radioactive sources can reduce their radiation dose.[2 marks]
Mark scheme
  1. 1.Recall the protection methods.
Any two of: keep a greater distance from the source (1); limit the time spent near the source (1); use shielding such as lead or wear protective clothing (1) (max 2)
8A hospital uses high-energy gamma radiation to treat a tumour deep inside a patient. Explain why gamma is suitable, how the treatment is targeted to limit harm, and why the benefits are judged to outweigh the risks.[3 marks]
Mark scheme
  1. 1.Link gamma penetration to reaching deep tissue.
  2. 2.Describe how healthy tissue is protected.
  3. 3.Weigh benefit against risk.
Gamma is very penetrating so it can reach a deep tumour from outside the body (1); the beams are aimed from different directions (or rotated) so they all meet at the tumour, giving it a high dose while healthy tissue receives a lower dose (1); although radiation can damage healthy cells and slightly raise cancer risk, killing the tumour is judged a greater benefit than the harm, so the treatment is justified (1)
9Explain why contamination by an alpha-emitting isotope is particularly dangerous, even though alpha radiation is stopped by a thin layer of skin.[4 marks]
Mark scheme
  1. 1.Contamination means source is inside or directly on the body.
  2. 2.Alpha is strongly ionising at short range.
  3. 3.Tissues near the source receive intense ionising radiation.
  4. 4.Cannot be blocked by skin once inside the body.
If an alpha-emitting isotope is inhaled or ingested, the source is inside the body and the alpha particles are emitted directly into surrounding tissue (1); alpha radiation is the most ionising type, causing a large number of ion pairs per millimetre, which can cause significant damage to the DNA of nearby cells (1); because the source is on or in the body there is no protective skin layer between the alpha emitter and the sensitive tissue, so the shielding argument that 'skin stops alpha' does not apply (1); this makes internal contamination with alpha emitters potentially more hazardous than external irradiation by beta or gamma sources (1)
10Describe how gamma radiation is used to sterilise medical instruments. Include the type of source used, why gamma is chosen over alpha or beta, and any practical considerations for the process.[4 marks]
Mark scheme
  1. 1.Gamma can penetrate sealed packaging to reach instruments.
  2. 2.Kills microorganisms by ionising damage to their DNA.
  3. 3.Alpha and beta lack penetrating power to reach inside sealed packages.
  4. 4.Source with suitable half-life and activity needed.
Medical instruments are sealed in their packaging and then exposed to high-energy gamma radiation from a cobalt-60 source (1); gamma is chosen because it is highly penetrating, allowing it to pass through the sealed packaging and reach all surfaces of the instrument to kill any microorganisms (1); alpha and beta would be absorbed by the packaging and would not reach the instruments (1); the source must have a high enough activity to deliver a sufficient dose in a reasonable time, and precautions must be taken to protect workers, such as keeping them at a distance and using lead shielding; instruments are not made radioactive because they are irradiated rather than contaminated (1)
11A beta-emitting isotope is used to monitor the thickness of paper leaving a factory's rollers. Explain how the detector reading changes if the paper becomes too thick or too thin, and describe how this information can be used in an automatic control system.[4 marks]
Mark scheme
  1. 1.Beta partially penetrates paper; correct thickness gives a set detector reading.
  2. 2.Thicker paper absorbs more beta; reading decreases.
  3. 3.Thinner paper absorbs less; reading increases.
  4. 4.Feedback signal from detector adjusts the rollers automatically.
At the correct thickness, a certain fraction of beta radiation passes through the paper to the detector, giving a calibrated reference count rate (1); if the paper is too thick, more beta is absorbed and the count rate at the detector falls below the reference level (1); if the paper is too thin, less beta is absorbed and the count rate rises above the reference level (1); the detector output is fed back to a control system that automatically adjusts the pressure on the rollers — if too thick, the rollers squeeze tighter; if too thin, they open slightly — maintaining the desired thickness without stopping the production line (1)
12Evaluate the risks and benefits of using radioactive tracers in nuclear medicine. In your answer, consider the properties of a suitable tracer, the benefit to the patient, and the steps taken to minimise risk. Include a discussion of whether irradiation or contamination is the relevant hazard.[4 marks]
Mark scheme
  1. 1.Describe what a tracer is and how it works.
  2. 2.Properties of a good tracer: gamma emitter, short half-life, biologically targeted.
  3. 3.Benefit: diagnosis of organ function without surgery.
  4. 4.Hazard: contamination (radioactive atoms inside body).
  5. 5.Risk minimisation: short half-life, low dose, suitable element.
A radioactive tracer is an isotope introduced into the body, often by injection; the patient is irradiated internally (contamination) because radioactive atoms are inside the body, not just exposed from outside (1); a suitable tracer should emit gamma radiation so it can pass out of the body to be detected by external cameras; it should have a short half-life (typically hours) so the activity decays quickly after the test, limiting the total dose to the patient (1); the tracer should be chemically chosen to concentrate in the organ being investigated, allowing doctors to image its function and detect disease without invasive surgery — a clear clinical benefit (1); risk is minimised by using the lowest effective dose, selecting a tracer with an appropriately short half-life, and avoiding tracers that concentrate in sensitive tissues such as bone marrow; the clinical benefit of diagnosis (detecting cancer, kidney disease, etc.) is judged to outweigh the small increase in cancer risk from the radiation dose, making the procedure ethically justified (1) — award max 4
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