OCR GCSE Physics A: Radiation hazards, medical uses, fission and fusion (J249) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions follow the OCR GCSE (9-1) Gateway Science Physics A specification (J249), Version 5.0 (July 2026), for first assessment in 2018. They cover statements P6.2a to P6.2e. Questions 1 to 3 are on P6.2a, which is assessed in both tiers. Questions 4 to 12 are on P6.2b to P6.2e, which are tested only in the Higher Tier papers, and are labelled “(Higher Tier only)”. Read the study guide first, or use the revision notes. Hub: OCR GCSE Physics. Checklist: printable checklist. Find weak spots with the free diagnostics.

Questions

1. State the difference between contamination and irradiation. [2]

2. For each situation, state whether it is contamination or irradiation.

(a) A technician breathes in radioactive dust released from a damaged container. [1] (b) A metal part is checked by placing a sealed gamma source on one side and a detector on the other. [1] (c) A person drinks milk that contains radioactive atoms from fallout. [1] (d) A person sits 3 m from a shielded, sealed source. [1]

3. A technician works with an alpha-emitting source.

(a) Explain why the risk is low while the source is sealed in a case. [2] (b) Explain why the risk is much greater if a sample of the same source is swallowed. [2]

4. (Higher Tier only) Waste A has a half-life of 20 minutes. Waste B has a half-life of 24 000 years. Each sample has the same number of undecayed nuclei and emits the same type of radiation.

(a) State which sample has the greater activity at first, and explain why. [2] (b) State which sample stays hazardous for longer, and explain what this means for how it is stored. [2]

5. (Higher Tier only) Radioactive material is spilt in a laboratory. The activity is 5600 Bq. The area is safe when the activity is 175 Bq or below. The half-life of the material is 4 days. Calculate how long it will be before the area is safe. [3]

6. (Higher Tier only) A smoke detector contains a small source of an alpha emitter with a half-life of about 430 years.

(a) Explain why a long half-life suits this use. [2] (b) Explain why an alpha emitter is suitable for a device used in homes. [1]

7. (Higher Tier only) A hospital wants a radioactive tracer to scan an organ. Four isotopes are considered.

Isotope	Radiation	Half-life
P	Alpha	6 hours
Q	Gamma	6 hours
R	Gamma	40 days
S	Gamma	3 seconds

(a) State which isotope is best and give three reasons. [3] (b) Give one reason each for rejecting the other three isotopes. [3]

8. (Higher Tier only) A patient is injected with a tracer of activity 720 MBq. Its half-life is 8.0 hours.

(a) Calculate the activity of the tracer after 24 hours, assuming none leaves the body. [3] (b) State one reason why the actual activity in the patient would be lower. [1]

9. (Higher Tier only) Radiotherapy is used to treat a tumour with gamma rays from an external source.

(a) Describe how the gamma rays treat the tumour. [2] (b) Explain why the beam is directed at the tumour from several different directions. [2] (c) Explain why the treatment has side effects. [1]

10. (Higher Tier only) Uranium-235 is used as a fuel in nuclear fission.

(a) State what a uranium-235 nucleus usually has to do before it splits. [1] (b) State two things, other than the smaller nuclei, that are released when the nucleus splits. [2] (c) Explain how a chain reaction can happen. [2]

11. (Higher Tier only) In a model of a chain reaction, each fission causes an average of 3 further fissions. One fission starts the chain (generation 0).

(a) Calculate the number of fissions in generation 5. [2] (b) Calculate the total number of fissions from generation 0 to generation 5 inclusive. [2] (c) State the average number of further fissions per fission that gives a steady release of energy. [1]

12. (Higher Tier only) Two nuclei of hydrogen-2 can fuse to form helium-3 and a neutron.

(a) Describe what nuclear fusion is and state what happens to some of the mass. [2] (b) Explain why fusion needs a very high temperature. [2] (c) Show that nucleon number and proton number are both conserved in ²H + ²H → ³He + ¹n. [2]

Answers

1. Contamination is the presence of radioactive atoms on or inside an object or person [1]. Irradiation is exposure to radiation from a source outside, without the radioactive atoms being transferred [1]. [2] Examiner insight: Answers that name what reaches the object (atoms or only radiation) tend to separate the two clearly; “contamination is worse” is a comparison, not a difference.

2. (a) Contamination, because the radioactive dust is taken into the body [1]. (b) Irradiation, because the source is sealed and only radiation passes through the part [1]. (c) Contamination, because radioactive atoms are inside the body [1]. (d) Irradiation, because only radiation reaches the person from the sealed source [1]. [4] Examiner insight: Giving the reason alongside each label is good practice, because a label alone does not show the idea of atoms being on or in the object.

3. (a) Alpha particles are stopped by the case, by skin and by a few centimetres of air [1]. Sealed, no radioactive atoms can get onto or into the technician [1]. (b) Inside the body there is no skin or air to stop the alpha particles [1]. They are strongly ionising and deposit all their energy in nearby living cells [1]. [4] Examiner insight: Stating that alpha is “harmless” loses the point; the stronger answer says that the risk depends on whether the source is inside or outside the body.

4. (a) Sample A [1]. For the same number of nuclei, a shorter half-life means the same fraction decays in less time, so the rate of decay is higher [1]. (b) Sample B [1]. Its activity falls very slowly, so it needs secure storage for a very long time [1]. [4] Examiner insight: A good answer links activity to rate and hazard to duration; saying that a long half-life is “safer” without the second idea gives only half the picture.

5. 5600 ÷ 175 = 32 [1]. 32 = 2⁵, so five half-lives are needed [1]. Time = 5 × 4 days = 20 days [1]. [3] Examiner insight: Writing the ratio, then the number of half-lives, then the time makes the working easy to follow, and a halving chain 5600, 2800, 1400, 700, 350, 175 confirms it.

6. (a) The activity falls only very slowly [1], so the source gives a steady output for many years without needing replacement [1]. (b) Alpha is stopped by a few centimetres of air or by the casing, so people nearby are not irradiated [1]. [3] Examiner insight: “Lasts a long time” is a weak answer; saying the activity stays almost constant explains why the detector keeps working.

7. (a) Isotope Q [1]. Gamma rays pass out of the body to the detector [1]. A half-life of hours is long enough for the scan but the activity falls quickly afterwards [1]. (b) P: alpha cannot leave the body, and would damage tissue [1]. R: the half-life is so long that the patient would stay radioactive for a long time [1]. S: it decays almost entirely in seconds, before the scan can be done [1]. [6] Examiner insight: Rejections work best when each is tied to a property in the table, so quote the radiation or half-life you are rejecting.

8. (a) 24 ÷ 8.0 = 3 half-lives [1]. 720 ÷ 2³ = 720 ÷ 8 [1]. Activity = 90 MBq [1]. (b) The body removes some of the tracer, for example in urine [1]. [4] Examiner insight: Showing the number of half-lives before dividing keeps the working checkable, and an answer of 90 with the unit MBq is clearer than a bare number.

9. (a) Gamma rays are aimed at the tumour [1]. The radiation is ionising and damages or kills cancer cells [1]. (b) Each beam passes through different healthy tissue, so each healthy region receives a low amount [1]. The beams all cross at the tumour, so the tumour receives a high total [1]. (c) Healthy cells that absorb radiation are also damaged [1]. [5] Examiner insight: For an explain question, the comparison “high at the tumour, low elsewhere” is the idea to state; “to cover the whole tumour” is a different and weaker point.

10. (a) It absorbs a neutron [1]. (b) Neutrons [1] and gamma radiation (or energy as kinetic energy of the fission products) [1]. (c) The neutrons released are absorbed by other uranium-235 nuclei [1], which split and release more neutrons, so the process repeats [1]. [5] Examiner insight: A chain reaction answer needs the neutrons as the link between one fission and the next; saying only “it keeps going” does not explain the mechanism.

11. (a) Each generation is 3 times the previous one, so generation 5 has 3⁵ [1] = 243 fissions [1]. (b) Total = 1 + 3 + 9 + 27 + 81 + 243 [1] = 364 fissions [1]. (c) 1 [1]. [5] Examiner insight: Listing the terms before adding them makes slips easy to spot, and noting that generation 0 counts as one fission avoids an off-by-one error.

12. (a) Two light nuclei combine into one heavier nucleus [1]. Some of the mass becomes energy carried by radiation [1]. (b) Nuclei are positively charged, so they repel each other [1]. At very high temperature they move fast enough to get close enough to fuse [1]. (c) Nucleon number: 2 + 2 = 4 and 3 + 1 = 4 [1]. Proton number: 1 + 1 = 2 and 2 + 0 = 2 [1]. [6] Examiner insight: Show a “show that” by writing both totals for each quantity, because a statement that “it balances” on its own does not show the check.

Where marks are usually lost

• Calling an irradiated object radioactive.
• Describing contamination as radiation rather than radioactive atoms on or in the object.
• Saying alpha is harmless or always dangerous, without separating outside from inside the body.
• Treating a long half-life as safer, or a short half-life as always harmless.
• Choosing an alpha emitter or a very long-lived source as a tracer.
• Forgetting the unit in activity answers, or the power of 2 in the working.
• Describing fusion as splitting, or fission as joining.
• Leaving out the neutron that starts fission, or the neutrons that continue the chain.
• Writing a bare “it balances” for a conservation check without both totals.

Next steps

• Revision notes
• Study guide
• OCR GCSE Physics hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

OCR, GCSE (9-1) Gateway Science Physics A (J249) specification, Version 5.0 (July 2026), for first assessment in 2018, topic P6.2 Uses and hazards.