Uses and Dangers of Radiation

What this lesson covers in the specification

Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.

• 7.14 — Uses of radioactivity in industry and medicine
• 7.15 — The difference between contamination and irradiation
• 7.16 — The dangers of ionising radiation and the problems of radioactive waste disposal

Specification section 7(b) Radioactivity — also taught in Alpha, Beta and Gamma, Nuclear Equations, Detecting Radiation and Background, Half-Life.

1 · Understand it

No exam language yet. The only question this section answers is: do I actually understand what is happening?

Every use of radioactivity on this page is a choice of two properties: which RADIATION, and what HALF-LIFE. Once you know what a source has to do, both follow — and exam questions almost always ask you to justify the choice rather than to recall it.

Choosing a source, in two questions

1. WHAT MUST THE RADIATION GET THROUGH? If it must pass out of the body or through a steel pipe, it has to be gamma. If it must be stopped by a thin sheet of paper or plastic, alpha is the only one that will notice a thin sheet at all. If it must pass through paper but be affected by a few millimetres of metal, beta is the answer.
2. HOW LONG MUST IT LAST? A medical tracer injected into a patient needs a half-life of hours — long enough to complete the scan, short enough that the patient is not left radioactive.
3. A thickness gauge in a factory runs continuously for years, so it needs a long half-life or it would have to be replaced constantly.
4. So the two properties answer two different questions, and a good answer names both: which radiation, and why; what half-life, and why.

Take the standard examples in turn. A THICKNESS GAUGE for paper or aluminium foil uses a BETA source on one side of the sheet and a detector on the other. Beta is right because it passes through paper but the amount getting through changes measurably if the thickness changes — alpha would be stopped entirely by any thickness, and gamma would pass through regardless, so neither could detect a change. The half-life must be long, so the reading does not drift as the source decays.

A MEDICAL TRACER is swallowed or injected, and its progress through the body is followed by a detector outside. It must be a GAMMA emitter, because gamma is the only one that reliably escapes the body to be detected, and because gamma does the least damage to the tissue it passes through. Its half-life must be SHORT — a few hours — so that the patient does not remain radioactive after the scan, but not so short that it decays before the scan is finished.

STERILISATION uses intense GAMMA radiation to kill bacteria on surgical instruments and on some food. The instruments can be sealed in their packaging first and irradiated through it, which is the whole advantage over heat: nothing has to be opened, and heat-sensitive plastics are not damaged. RADIOTHERAPY uses focused gamma beams to kill cancer cells, rotating the beam around the patient so that the tumour receives the full dose at the point where the beams cross while any single piece of healthy tissue receives much less. And a SMOKE ALARM uses a weak ALPHA source: the alpha ionises the air in a small gap so a tiny current flows, and smoke particles absorb the alpha and interrupt the current, setting off the alarm. Alpha is used precisely because it cannot travel more than a few centimetres, so it never leaves the device.

Now the distinction the specification names explicitly, statement 7.15, and it is worth being exact about. IRRADIATION is being EXPOSED to radiation from a source outside you. The radiation arrives, does whatever damage it does, and when you move away or the source is removed, it stops — you do not become radioactive yourself. CONTAMINATION is having radioactive MATERIAL on you or inside you. The source has come with you, and it goes on emitting until it is removed or has decayed.

Think of it like standing in the rain against getting mud on your boots

Standing in the rain, you get wet for as long as you stand there, and stepping indoors ends it immediately — nothing has come with you. That is irradiation. Getting mud on your boots is different: walk indoors and the mud comes too, and it will still be there tomorrow unless somebody cleans it off. That is contamination. The distinction explains the safety measures, which otherwise look inconsistent. Lead shielding and distance protect against the rain, and they are useless against the mud. Gloves, sealed sources and handling with tongs stop the mud getting on you, and do nothing about the rain. You need both because they are different problems.

The dangers themselves come from ionisation. Radiation passing through living tissue knocks electrons off the molecules in cells, which can damage them. A LOW dose may damage the DNA in a cell without killing it, and a cell with damaged DNA may go on to divide uncontrollably — that is cancer, and it may appear years later. A HIGH dose kills cells outright, causing radiation sickness, burns and, at sufficient doses, death within days or weeks.

Finally the waste problem, which is a direct consequence of the half-life page. The most troublesome waste from a reactor contains isotopes with half-lives of thousands of years, so it cannot simply be stored until it is safe — nothing built by anyone has lasted that long. High-level waste is therefore vitrified into glass blocks, sealed in metal containers, and buried in deep, geologically stable rock, well away from groundwater. The technical difficulty is real, but the harder problem is that any storage decision has to hold for longer than recorded history, including the question of how to warn people who will not speak any language now spoken.

2 · Grade 9 Notes

A different job from the section above. You have already understood it; this is the precise set of things to LEARN — definitions to reproduce word for word, processes in order, equations with units, and the answers that score full marks.

Statement 7.15 — the two words examiners test

Irradiation

Being exposed to radiation from a source outside the body. It stops when the source is removed, and the person does not become radioactive.

Contamination

Having radioactive material on the skin or inside the body. It continues until the material is removed or has decayed.

Dose

A measure of the energy absorbed by tissue from ionising radiation. A higher dose means a greater risk of damage.

Irradiation against contamination

Statement 7.14 — the uses, with the reason for each choice

• THICKNESS GAUGE — BETA, long half-life. Beta is partly absorbed so the reading changes with thickness; alpha would be stopped entirely and gamma would pass regardless
• MEDICAL TRACER — GAMMA, short half-life of a few hours. Gamma escapes the body to be detected and does least damage; a short half-life means the patient is not left radioactive
• STERILISING instruments and food — intense GAMMA. It penetrates sealed packaging, so nothing need be opened and heat-sensitive items are not damaged
• RADIOTHERAPY — focused GAMMA beams rotated about the patient, so the tumour gets the full dose where the beams cross and healthy tissue much less
• SMOKE ALARM — weak ALPHA, long half-life. Alpha ionises the air so a small current flows, and smoke interrupts it; its short range means it never leaves the device

Justifying a choice of source

1. Ask what the radiation must pass through, and what must stop it.
2. Choose the radiation whose penetrating power matches that requirement exactly.
3. Ask how long the source must remain useful.
4. Choose a long half-life for permanent industrial use, a short one for anything entering a body.
5. State BOTH choices with a reason for each — the marks are usually split between them.

The dangers, and how they differ with dose

• Ionising radiation knocks electrons off molecules in cells, damaging them
• A LOW dose may damage DNA without killing the cell, which can lead to cancer years later
• A HIGH dose kills cells outright, causing radiation sickness and burns, and can be fatal
• Protection against IRRADIATION: distance, shielding, and limiting exposure time
• Protection against CONTAMINATION: sealed sources, gloves, tongs, and never eating near a source

Why radioactive waste is difficult to dispose of

• The most troublesome isotopes have half-lives of THOUSANDS OF YEARS, so it cannot be stored until it is safe
• It must be kept out of contact with groundwater, or the contamination spreads
• High-level waste is vitrified into glass, sealed in metal containers, and buried deep in stable rock
• The containment must outlast any structure or institution ever built
• Even warning future people is a problem, since no current language can be relied on

Model answer [4 marks]

A source is used in a factory to monitor the thickness of aluminium foil. State which radiation and which half-life should be chosen, and explain both choices. [4]

A beta emitter should be used, because beta radiation is partly absorbed by a thin sheet of aluminium, so the amount reaching the detector changes if the thickness changes. Alpha radiation would be stopped completely by any thickness of foil and gamma radiation would pass through almost unaffected, so neither could detect a change. The source should have a long half-life so that its activity does not fall noticeably during use, which would otherwise be mistaken for a change in the thickness of the foil and would mean recalibrating or replacing the source constantly.

Model answer [4 marks]

Explain the difference between irradiation and contamination, and give one precaution against each. [4]

Irradiation is being exposed to radiation from a source outside the body; it stops as soon as the person moves away or the source is removed, and the person does not become radioactive. Contamination is having radioactive material on the skin or inside the body, so the source remains with the person and continues to emit radiation until it is removed or has decayed. A precaution against irradiation is to keep as far as possible from the source and use lead shielding. A precaution against contamination is to keep sources sealed and handle them with long tongs, and never to eat or drink where sources are used.

Not this: Someone who has been irradiated becomes radioactive themselves and is dangerous to others.

This: Irradiation leaves nothing behind. The radiation passes through, does its damage and stops when the source is removed. Only CONTAMINATION — radioactive material on or in the person — makes someone a source themselves.

Mark-losing trap. A tracer needs GAMMA and a SHORT half-life; a gauge needs BETA and a LONG one. Name both and give both reasons.

Mark-losing trap. Irradiation stops when the source goes. Contamination comes with you.

Mark-losing trap. Shielding and distance defend against irradiation only. Gloves and sealed sources defend against contamination.

Mark-losing trap. Waste is hard to store because the half-lives are in THOUSANDS of years — longer than anything ever built has lasted.

3 · Prove it — the five questions

The five questions climb Grade 6 → Grade 7 → Grade 8 → Grade 9 → Grade 9 challenge, and are marked inside Incandio on your own device, by rule, with an authored diagnosis of the mistake you actually made. The mark schemes stay in the app so that the practice is worth doing; the questions themselves are here.

1. Grade 6 · State [1 mark] — A radioactive tracer is injected into a patient and followed by a detector outside the body. Which radiation should it emit?
2. Grade 7 · Explain [3 marks] — A patient is treated with a gamma beam from outside their body. Afterwards a relative asks whether it is safe to sit near them. Explain the answer.
3. Grade 8 · Explain [3 marks] — A smoke alarm contains a weak alpha source. Explain why alpha is used rather than beta or gamma.
4. Grade 9 · Explain [6 marks] — Select every statement that belongs in a full-mark explanation of the choice of radiation and half-life for a radioactive tracer used to follow blood flow in a patient.
5. 9+ · Evaluate [6 marks] — A laboratory proposes storing high-level radioactive waste in sealed steel drums inside a guarded warehouse, arguing that this is cheaper than deep burial and that 'the guards can simply be replaced as generations pass'. Select every statement that belongs in a full-mark evaluation.

The people behind this science

Two ways into the same idea — the one who put it to use and paid for it, and the one whose accidental burn was the first evidence of the danger. Inside Incandio each of them answers knowing exactly which lesson you have just finished.

Marie Curie — the one who put it to use and paid for it

The medical uses on this page begin with her. During the First World War she raised money for around twenty mobile radiography units, trained women to operate them, learned to drive so she could take one to the front herself, and had X-ray equipment installed at hundreds of field stations — probably a million wounded men were examined with them. She also worked for years with radium without protection, refused for a long time to accept that it was harming her, and died of an illness almost certainly caused by that exposure. Her notebooks remain too radioactive to handle freely. She is the right person to ask about benefit and harm from the same material.

• “Why did you take X-ray units to the battlefield yourself?”
• “How does radiation help a surgeon find a bullet?”
• “Did you know the radium was hurting you?”
• “Why did you refuse to patent the process for isolating radium?”
• “How should a scientist weigh a use against a danger?”

Henri Becquerel — the one whose accidental burn was the first evidence of the danger

The dangers on this page were discovered by accident, and Becquerel's was the first clear case. He carried a small tube of radium in his waistcoat pocket for a few hours while travelling, and some days later found a burn on the skin beneath it, in the shape of the tube. Pierre Curie deliberately repeated it on his own arm to time the effect. That burn is the beginning of radiobiology, and it also points directly to why radiotherapy works: if radiation kills healthy tissue, then aimed properly it will kill a tumour. He is the right figure to ask how a hazard and a treatment turn out to be the same fact.

• “What happened to your skin after carrying radium in your pocket?”
• “How long was it before you connected the burn to the tube?”
• “Why would something that burns skin be useful in medicine?”
• “Did anyone take precautions in those early years?”
• “What did Pierre Curie do to his own arm, and why?”

Carry on through the course

• Previous lesson: Half-Life
• Next lesson: Nuclear Fission
• Atomic Structure and Isotopes — A nucleus ten thousand times smaller than the atom around it, and why two atoms of the same element can weigh different amounts.
• Alpha, Beta and Gamma — Three emissions from unstable nuclei, arriving at random — and why the one that is easiest to stop is the one to be most careful with.
• Nuclear Equations — What each kind of decay does to the numbers — and why losing a negative particle makes the charge go up.
• Detecting Radiation and Background — How you measure something invisible, and why the counter clicks even with no source in the room.
• Half-Life — Half of what is left, every time — which is why a radioactive sample never quite runs out.
• All of Physics · Physics key terms · required practicals · equations · Incandio Science · The 4PH1 specification