PhysicsICSE Class 10 · Radioactivity

Uses and Hazards of Radioactivity: Radioisotopes, Background Radiation and Safety (ICSE Class 10)

Updated 16 October 2026 · Fact-checked

Radioisotopes are used to treat cancer (cobalt-60), study the thyroid (iodine-131), date ancient remains (carbon-14), trace leaks and check the thickness of sheets. The same radiation ionises living cells, causing burns, cancer and genetic defects, so sources are handled with tongs, kept in lead and used for the shortest possible time.

Understand Uses and Hazards of Radioactivity

Radioisotopes. A radioisotope is an isotope with an unstable nucleus, so it is radioactive. Some occur naturally (carbon-14, potassium-40, uranium-238); others are made artificially in nuclear reactors (cobalt-60, iodine-131, sodium-24). Chemically a radioisotope behaves exactly like the stable isotope of the same element, but its radiation lets us detect where it goes.

Choosing the radiation for a job. Each use depends on a property of α, β or γ:

γ rays are the most penetrating: they pass through skin, packaging and metal.
β particles pass through paper but are partly absorbed by thin sheets, so the amount getting through depends on thickness.
α particles are stopped by a sheet of paper or a few cm of air, but ionise strongly.

Uses of radioisotopes.

Field	Radioisotope	Radiation used	Use
Medicine	cobalt-60	γ	radiotherapy: kills cancer cells in a deep tumour
Medicine	iodine-131	β, γ	diagnosis and treatment of thyroid disorders (the thyroid absorbs iodine)
Medicine and food	cobalt-60	γ	sterilising sealed syringes, dressings and food: γ kills microbes through the packaging
Archaeology	carbon-14	β	carbon dating: estimating the age of wood, bones and cloth
Industry and medicine	sodium-24	γ	tracer: locating leaks in buried pipes; checking blood flow
Industry	a β source	β	thickness gauge for paper, plastic and metal foil
Industry	a γ source	γ	detecting flaws in welds and castings
Agriculture	phosphorus-32	β	tracer to study how plants take up fertiliser
Home	americium-241	α	smoke detector: α ionises the air in a small chamber

A radioisotope put inside the body should be short-lived and give out radiation that can be detected outside (γ), so the patient receives as little dose as possible.

Harmful effects. Radiation ionises the atoms of living cells. This can kill cells or damage their DNA.

Somatic effects (on the exposed person): skin burns, hair loss, radiation sickness, cataract, cancer such as leukaemia.
Genetic effects (on future generations): mutations in reproductive cells can be passed on as inherited defects.
The damage depends on the dose, the time of exposure, the type of radiation and the part of the body exposed. Outside the body, γ is the most dangerous because it penetrates to the organs; inside the body (swallowed or breathed in), α is the most dangerous because it ionises most strongly.

Background radiation. Low-level radiation is always present around us.

Natural: cosmic rays from space; radioactive rocks and soil; radon gas seeping out of rocks such as granite; potassium-40 and carbon-14 in food and in our bodies.
Man-made: medical X-rays and scans; radioactive fallout from nuclear tests and accidents; small leaks from nuclear plants.

Background radiation must be subtracted from every reading taken with a detector.

Radiation pollution. Over-use of X-rays and radioactive fallout from nuclear plants are sources of radiation pollution. Fallout contains isotopes such as strontium-90 and caesium-137. (Extension: these isotopes are not named in the syllabus, which asks only for fallout as a source. Strontium is chemically like calcium, so the body deposits strontium-90 in the bones.)

Safety precautions. The three rules are time, distance and shielding: keep exposure short, stay as far away as possible and put absorbing material in between.

Handle sources with long tongs, never with hands.
Store sources in thick lead containers; use lead or concrete walls around strong γ sources.
Wear lead aprons and a film badge (dosimeter) that records the dose received.
Do not eat, drink or smoke where radioactive materials are used; display the radiation warning sign.

Nuclear waste. Spent fuel and other nuclear waste stay radioactive for thousands of years. Safe disposal: seal it in thick glass and steel containers and bury it deep underground in stable rock, far from groundwater and earthquake zones; monitor the site. The syllabus stresses that safety measures must be strictly reinforced at nuclear plants.

Remember. Radioactive decay is a nuclear process: heating, cooling, pressure or chemical reactions do not change the rate at which a radioisotope decays.

Uses and Hazards of Radioactivity: formulas and key facts

Radiation for a job: γ: radiotherapy, sterilising, tracers, flaw detection
β: thickness gauge, carbon dating, P-32 tracer
α: smoke detector; Match the penetrating power to the job.
Harmful effects: Somatic: burns, radiation sickness, cancer (leukaemia) | Genetic: mutations passed to offspring; Damage depends on dose, time, type and organ.
Background radiation: Natural: cosmic rays, rocks and soil, radon, K-40 in the body | Man-made: X-rays, fallout, nuclear plants; Subtract it from every count.
Safety: Time short
Distance large
Shielding lead
Tongs, lead containers, film badges; Waste: sealed and buried deep in stable rock.
Corrected count: $corrected count = measured count - background count$; Both per minute.

Time	short
Distance	large
Shielding	lead
	Tongs, lead containers, film badges

How to solve Uses and Hazards of Radioactivity questions

Most questions on uses and hazards are answered by linking one property of the radiation to the job or the danger.

1Ask what the radiation must do: pass through the body or packaging (γ), be partly absorbed by a thin sheet (β), or ionise a small volume of air (α).
2For a use inside the body, choose a short-lived γ emitter that can be detected from outside.
3When asked for the use of a named isotope, give the use specific to that isotope (C-14: dating; I-131: thyroid; Co-60: radiotherapy or sterilising).
4For a hazard, name the effect (burns, cancer, mutation) and say whether it is somatic or genetic.
5For a precaution, say what it does: lead absorbs, distance reduces exposure, a film badge measures the dose.
6For detector readings, subtract the background count first, then compare.

Uses and Hazards of Radioactivity in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Sterilised syringes

Suppose you notice that a sealed packet of disposable syringes says 'Sterilised by gamma radiation'. The packet is never opened before it reaches the clinic.

Why is γ radiation used, and does the syringe become radioactive?

Try it first, then show the solutionSolution

γ rays are very penetrating, so they pass through the sealed plastic and kill bacteria on the syringe inside.
They do not change the nuclei of the plastic, so the syringe does not become radioactive.
Because the packet stays sealed, no new germs can enter afterwards.

Answer: γ rays penetrate the packet and kill microbes; the syringe does not become radioactive.

Memory hook: Gamma goes through the wrapper.

Cosmic rays at cruising height

Suppose you read that airline pilots and cabin crew receive more background radiation each year than people who work on the ground.

Explain why, and say whether this source is natural or man-made.

Try it first, then show the solutionSolution

Cosmic rays from space reach the earth all the time; the atmosphere absorbs much of them.
At cruising height there is far less air above the aircraft to absorb them, so more radiation reaches the crew.
Cosmic rays are a natural source of background radiation.

Answer: Less air above to absorb cosmic rays; a natural source.

Memory hook: Higher up, thinner shield.

Tricks to remember Uses and Hazards of Radioactivity

Short memory aids. Say each one aloud once, then use it on a question the same day.

Time, Distance, Shielding
'TDS': less Time, more Distance, more Shielding.
Use it when: Safety precautions.
Gamma goes through, beta gauges, alpha alarms
γ passes through (sterilising, therapy), β measures thickness, α sets off the smoke alarm.
Use it when: Matching radiation to uses.
Somatic = self, genetic = generations
Somatic effects hurt the person exposed; genetic effects reach the children.
Use it when: Classifying harmful effects.
Subtract the sky and the stones
Background (cosmic rays and rocks) is always there: subtract it first.
Use it when: Detector readings.

Uses and Hazards of Radioactivity: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Sterilising sealed packets · 1 mark · MCQBoard level

Surgical dressings are sterilised after they have been sealed in plastic packets. The radiation used is:
(a) α particles
(b) β particles
(c) γ rays
(d) visible light

Try it first, then show the solutionSolution

The radiation must pass through the sealed packet to kill microbes inside: only γ rays are penetrating enough.

Answer: (c) γ rays

Example 2: Natural or man-made? · 2 marks · Short answerBoard level

Classify each source of background radiation as natural or man-made: (a) cosmic rays, (b) fallout from nuclear weapon tests, (c) radon gas from granite, (d) a chest X-ray, (e) potassium-40 in bananas.

Try it first, then show the solutionSolution

Natural sources come from space, rocks or living things: (a), (c), (e). (1)
Man-made sources come from human activity: (b), (d). (1)

Answer: Natural: (a), (c), (e). Man-made: (b), (d).

Example 3: A tracer in the bloodstream · 3 marks · Short answerHarder board level

A doctor injects a small amount of sodium-24 ( $_{11}^{24} Na$ , a β and γ emitter) in salt solution into a patient's arm to check whether blood flows freely to the leg.
(a) Write the equation for the β decay of sodium-24, naming the product as Mg.
(b) Why must the radiation detected outside the body be γ and not β?
(c) Why is a short-lived isotope chosen?

Try it first, then show the solutionSolution

(a) $_{11}^{24} Na \to_{12}^{24} Mg +_{- 1}^{0} e$ (A unchanged, Z rises by 1). (1)
(b) β particles are absorbed by the body tissues; γ rays pass out through the skin and reach the detector. (1)
(c) Its activity dies away within a few days, so the patient's total dose stays small. (1)

Answer: (a) ²⁴₁₁Na → ²⁴₁₂Mg + ⁰₋₁e (b) Only γ passes out through the body (c) It keeps the patient's dose small

Example 4: Somatic or genetic? · 3 marks · Short answerHarder board level

Suppose two workers were exposed to radiation in an accident. Worker P developed skin burns and, years later, leukaemia. Worker Q stayed healthy, but his child was born with an inherited defect traced to a mutation.
(a) Classify each effect as somatic or genetic.
(b) Why can a genetic effect appear in a child even when the parent shows no illness?

Try it first, then show the solutionSolution

(a) P: somatic effects (on the exposed person's own body cells). (1)
Q's child: a genetic effect. (1)
(b) The radiation damaged the DNA of Q's reproductive cells; the mutation was passed on to the child, though Q's other cells were not harmed enough to cause illness. (1)

Answer: (a) P: somatic; Q's child: genetic (b) A mutation in reproductive cells is inherited.

Example 5: A thickness gauge · 3 marks · Short answerHarder board level

In a paper mill, a β source is placed below a moving sheet of paper and a detector above it. The detector normally reads 600 counts per minute. One morning the reading rises to 680 counts per minute.
(a) Has the paper become thicker or thinner? Explain.
(b) Why would an α source not work here, and why would a γ source be unsuitable?

Try it first, then show the solutionSolution

(a) More β particles are getting through, so less is being absorbed: the paper has become thinner. (1)
(b) α particles would all be stopped by the paper, giving no reading at any thickness. (1)
γ rays would pass through almost completely, so small changes in thickness would hardly change the count. (1)

Answer: (a) Thinner (count rose by 80 per minute) (b) α is stopped completely; γ hardly changes

Example 6: Case study: background in two rooms · 4 marks · Case-basedHOTS / competency

Suppose a student measures the background count in a granite-floored basement as 48 per minute and in a top-floor classroom as 20 per minute. The same sealed source, held at the same distance from the detector, gives 348 per minute in the basement and 320 per minute in the classroom.
(a) Find the corrected count due to the source in each room.
(b) Why is the background higher in the basement?
(c) What do the two corrected counts show about the source?
(d) Name two sources of background radiation present in both rooms.

Try it first, then show the solutionSolution

(a) Basement: $348 - 48 = 300$ ; classroom: $320 - 20 = 300$ counts per minute. (1)
(b) Granite contains traces of uranium, whose decay gives radon gas; radon collects in closed, low rooms and adds to the background. (1)
(c) The corrected counts are equal: the source gives out radiation at the same rate wherever it is; only the background differs, which is why it must be subtracted. (1)
(d) Any two: cosmic rays; potassium-40 and carbon-14 in our bodies and food; radioactive traces in rocks and building materials. (1)

Answer: (a) 300 per minute in each room (b) Radon from the granite collects in the basement (c) The source emits at the same rate; only the background differs (d) e.g. cosmic rays; K-40 in the body

Example 7: Designing a waste store · 4 marks · Long answerHOTS / competency

Spent fuel from a nuclear plant contains caesium-137 ( $_{55}^{137} Cs$ ), a β emitter.
(a) Write its decay equation, naming the product as Ba.
(b) A proposal is to store such waste in steel drums in a shallow pit near a river. Give two objections and describe a safer method.

Try it first, then show the solutionSolution

(a) $_{55}^{137} Cs \to_{56}^{137} Ba +_{- 1}^{0} e$ . (1)
(b) Drums can corrode over the very long time the waste stays radioactive, and leaking material could reach the river and enter drinking water and food chains. (1)
A shallow pit is easily disturbed and radiation could reach people nearby. (1)
Safer: seal the waste in glass and thick steel containers and bury them deep underground in stable rock, far from groundwater, with regular monitoring. (1)

Answer: (a) ¹³⁷₅₅Cs → ¹³⁷₅₆Ba + ⁰₋₁e (b) Corrosion and leakage into water; easily disturbed. Seal and bury deep in stable rock away from water.

Where students lose marks in Uses and Hazards of Radioactivity

The slips examiners see most often, and what to write instead.

Mistake: Listing stable isotopes as radioisotopes
CISCE examiners' comments, 2024 Q2(i): asked which of O-16, C-14, N-14 and He-4 is a radioisotope, candidates wrote other isotopes such as He-4 or O-16 along with C-14.
Wrong working
'C-14 and He-4 are radioisotopes.'
Right working
'Only C-14 is a radioisotope.'
Do this: Pick only the unstable isotope.
Usually costs: 1 mark.
Mistake: A general use instead of the isotope's own use
CISCE examiners' comments, 2024 Q2(i): candidates gave a generalised use of radioisotopes instead of one specific to C-14.
Wrong working
'C-14 is used in medicine and industry.'
Right working
'C-14 is used in carbon dating of ancient remains.'
Do this: Learn one use per named isotope.
Usually costs: 1 mark.
Mistake: Thinking surroundings change the decay rate
CISCE examiners' comments, 2024 Q1(xiii): candidates associated radioactive decay with chemical reactions that depend on the physical environment.
Wrong working
'In a vacuum the decay rate decreases.'
Right working
'The decay rate is unchanged; it is a nuclear process.'
Do this: No temperature, pressure or chemical change affects radioactive decay.
Usually costs: 1 mark.
Mistake: Vague precautions
'Be careful' or 'avoid radiation' earns nothing; the marking scheme expects a named action.
Wrong working
'Stay safe from radiation.'
Right working
'Handle with long tongs; store in lead containers; wear a film badge.'
Do this: Name the object or action and what it does.
Usually costs: 1 mark each.

Exam tips

For 'one use of X', give the use that belongs to that isotope, not a general list.
Say why a radiation suits a use: γ for penetration, β for thickness, α for ionising air.
Write 'somatic' or 'genetic' when classifying an effect, then give an example.
In detector questions, subtract the background count before comparing readings.

Practice questions on Uses and Hazards of Radioactivity

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
A household smoke detector contains a small source of:
(a) cobalt-60
(b) americium-241
(c) iodine-131
(d) carbon-14
Hint
It gives out α particles that ionise the air.
Answer
(b) americium-241
Q2 · 1 mark · Very short answerBoard level
What is meant by a radioisotope?
Hint
Stable or unstable nucleus?
Answer
An isotope whose nucleus is unstable, so it gives out radiation (α, β or γ) as it decays.
Q3 · 1 mark · Very short answerBoard level
Why are radioactive sources kept in thick lead containers when not in use?
Hint
What does lead do to γ rays?
Answer
Lead absorbs the radiation, including most of the penetrating γ rays, so little escapes.
Q4 · 2 marks · Short answerBoard level
Why must people not eat, drink or smoke in a laboratory where radioactive sources are used?
Hint
Inside the body there is no dead skin layer.
Answer
Radioactive material on the hands or in the air could be swallowed or breathed in. Inside the body it irradiates living cells directly, and α and β particles, which ionise strongly, then do great damage.
Q5 · 2 marks · Short answerHarder board level
Strontium-90 ( $_{38}^{90} Sr$ ) in radioactive fallout is a β emitter. (Extension example: strontium-90 is not named in the syllabus.) (a) Complete: $_{38}^{90} Sr \to_{?}^{90} Y +_{- 1}^{0} e$ . (b) Strontium is chemically similar to calcium. Why is strontium-90 especially harmful if it enters the food chain?
Hint
Where does the body store calcium?
Answer
(a) Z = 39: $_{39}^{90} Y$ . (b) The body treats strontium like calcium and deposits it in the bones, where its radiation keeps damaging the bone marrow for years.
Q6 · 2 marks · Short answerHarder board level
Food irradiated with γ rays from cobalt-60 keeps longer. Explain why, and why the food does not become radioactive.
Hint
What do γ rays do to microbes, and to nuclei?
Answer
γ rays kill the bacteria and fungi that spoil food. They do not change the nuclei of the atoms in the food, so no radioactive nuclei are produced.
Q7 · 2 marks · Short answerHarder board level
A laboratory notice says: 'Wear a lead apron; you may then hold the source in your hand for as long as you need.' Point out two faults in this rule and give the correct practice for each.
Hint
Time and distance.
Answer
Holding the source by hand leaves no distance between it and the body: use long tongs, since exposure falls with distance. 'As long as you need' lets the dose build up: keep the handling time as short as possible. (A lead apron does not protect the hands.)
Q8 · 2 marks · Short answerHarder board level
During a dental X-ray, the patient stays in the chair while the radiographer goes behind a lead screen. Why does the radiographer take this precaution when the patient does not need to?
Hint
One X-ray against hundreds a week.
Answer
The patient is exposed briefly, only now and then. The radiographer takes many X-rays every day, so without shielding the dose would add up to a harmful level. Lead absorbs the X-rays.
Q9 · 3 marks · Short answerHOTS / competency
Three sources are available: A emits only α and lasts for centuries; B emits only β and lasts for years; C emits only γ and loses most of its activity in a day. Which would you choose for (a) a smoke detector, (b) a gauge for the thickness of plastic film, (c) a tracer injected into a patient? Give a reason for (c).
Hint
Match penetration and lifetime to the job.
Answer
(a) A (α ionises air; long-lasting). (b) B (β is partly absorbed by thin film). (c) C: γ escapes the body to reach the detector, and its short life keeps the patient's dose small.
Q10 · 2 marks · Short answerHOTS / competency
In radiotherapy, the γ source is often moved around the patient so that its beam enters from many directions, always aimed at the tumour. Explain how this helps.
Hint
Which tissue lies in every beam?
Answer
Every beam passes through the tumour, so the tumour receives the dose of all the beams added together. Each part of the healthy tissue around it lies in only one or a few beams, so it receives a much smaller dose. Cancer cells are killed while healthy tissue is spared.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Radiation used to find flaws in welds?Show answer
γ rays.
2.A natural radioisotope inside our bodies?Show answer
Potassium-40 (also carbon-14).
3.Radiation used in a paper thickness gauge?Show answer
β particles.
4.Is hair loss after a radiation accident somatic or genetic?Show answer
Somatic.
5.Why is γ, not α, used to sterilise sealed packs?Show answer
γ penetrates the packaging; α would be stopped.
6.One man-made source of background radiation?Show answer
Medical X-rays (or fallout from nuclear tests and accidents).

Uses and Hazards of Radioactivity: frequently asked questions

Why do smoke detectors use an α source rather than a γ source?

α particles ionise the air in the small chamber very strongly, giving a steady current that smoke interrupts. They are stopped by a few cm of air and the casing, so the detector is safe in a home; γ rays would ionise little and would pass out of the detector.

Does an X-ray make the patient radioactive?

No. X-rays are produced by a machine, not by radioactive nuclei. They do not change the nuclei of the body, so once the machine is switched off there is no radiation and the patient is not radioactive.

Does the ICSE syllabus need radiation dose units?

No. The 2027 syllabus asks for uses, harmful effects, safety precautions, background radiation, X-rays and fallout as radiation sources, and safe disposal of nuclear waste.