Nuclear physics (A-level only) questions

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• AQA 7408 · June 2025 · Paper 2 · Q3 · 11 marks

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  Question 3 was about radioactive decay set in the context of a radioisotope thermoelectric generator used to power a Mars rover. This question was the most accessible on the paper with a mean mark of around two thirds of the total marks.

  Text version

  A Mars vehicle uses a radioisotope thermoelectric generator (RTG) that initially contains 3.23 x 10^24 plutonium-238 atoms.

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• AQA 7408 · June 2024 · Paper 2 · Q4 · 5 marks

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  [04.2] Most students could name relevant properties of the coolant. This question was answered well, although some students wrote about irrelevant properties. As there is a range of liquid coolants used in nuclear reactors, including sodium, any relevant properties to any of these reactors were accepted. A few students failed to gain marks due to suggesting the wrong value for the property, eg that a low specific heat capacity was desirable rather than a high one. As the question only asked the students to state the properties that should be considered, students did not need to say whether a property required a high or low value, but when that information was supplied it had to be correct.

  Text version

  A nuclear reactor uses a coolant that circulates through the reactor core and a heat exchanger.

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• AQA 7408 · June 2024 · Paper 2 · Q7 · 10 marks

  10 marks

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  [07.3] This question was reasonably accessible. However, many students who wrote about handling the radioactive source with tongs, did not mention that the tongs had to be long. The measures described had to be ones that are relevant to sources used in schools. Students were then asked to consider how their safety measure could be adapted to a much more active source used in a hospital. Students were not expected to be familiar with a hospital setting (although those who were could use this knowledge), but rather to make a reasonable suggestion based on the activity given. Many students were able to make reasonable suggestions here.

  Text version

  A model of radioactive decay uses 900 identical n-sided dice. All dice are thrown and every die showing 1 is removed; the process is repeated. The following observations are plotted as separate crosses on a logarithmic vertical scale, with no best-fit line drawn: (throw, N) approximately (0,900), (1,700), (2,500), (3,400), (4,285), (5,210), (6,165), (7,130), (8,95), (9,75), (10,50), (11,42), (12,33), (13,27), (14,22), (15,16), (16,14), (17,10), (18,7), (19,6).

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• AQA 7408 · June 2023 · Paper 2 · Q4 · 8 marks

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  [04.2] Many students knew that the energy provided both to the electron and the argon ion was the same. Using this information to calculate the ratio of speeds then contained errors and so marks were missed by many. A significant minority (more than 10% of students) made no attempt at answering this question.

  Text version

  Figure 4 shows a spark detector used to detect alpha particles. Figure 4 The detector consists of a metal mesh placed 5.0 mm above a wire. A potential difference of 4000 V is applied between the mesh and the wire. Molecules in the air between the mesh and the wire are ionised by an alpha particle and a spark is produced. Figure 5 shows equipotentials between the mesh and the wire. Figure 5

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• AQA 7408 · June 2023 · Paper 2 · Q7 · 10 marks

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  [07.4] A majority of students could determine the initial and final kinetic energies in similar units and go on to obtain the correct answer. Re-arranging the equation did not pose much of a difficulty. It was most common for students to work with energies in J. Some of these made errors in converting from eV and some did not use the correct expression for the energy of a thermal neutron. There was also a significant number (nearly 9%) who had no idea how to start.

  Text version

  A neutron-moderator collision is modelled by neutron glider N of mass m_N striking stationary moderator glider M of mass m_M and rebounding. A graph gives rebound-speed ratio v/u against mass ratio m_M/m_N; at mass ratio 12, v/u is about 0.85.

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• AQA 7408 · June 2022 · Paper 2 · Q6 · 10 marks

  10 marks

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  [06.4] Only a minority of students understood why the fission products would be neutron-rich. Even the ones who did sometimes failed to gain this mark by simply stating they had more neutrons than protons. Then there was a lack of knowledge by many about what radiation would result from this fact. Also many thought the initial decay of the two fission products would be different. Finally, only about half the students made any reference to Figure 11 even though this was requested in the question. Section B There was a good spread in the performance on the multiple-choice section. Questions 16, 17, 24, 25 and 29 received correct answers from less than 40% of students. For question 24 it was less than 20%.

  Text version

  A binding-energy-per-nucleon graph rises steeply for light nuclei, peaks near iron-56, then falls slowly for heavy nuclei. A heavy nuclide X lies well to the right of the peak. A separate N-against-Z graph shows the band of stable nuclides; heavy neutron-rich fission fragments lie above the stable band.

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• AQA 7408 · November 2021 · Paper 2 · Q6 · 9 marks

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  [06.2] This was a question on which most students easily scored at least one mark. Some made it much more difficult for themselves by converting each mass separately instead of just converting the final mass difference.

  Text version

  Fusion reaction helium-3 + oxygen-17 -> neon-20 uses nuclear masses 3.01603 u,16.99913 u,19.99244 u. A contact model uses centre separation 5.1 x 10^-15 m. A competing reaction fuses helium-3 with sulphur-34.

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• AQA 7408 · November 2021 · Paper 3A · Q1 · 16 marks

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  The question was set in the context of Required Practical Activity 12. The demand of question 01.2 was not much beyond GCSE so it was unsurprising that the mean mark (75% of the maximum) was much higher than for any other part. In question 01.3 we asked students to explain whether the data indicate an inverse-square relationship. It was encouraging that 75% could suggest calculations that would lead to a conclusion. However, in rejecting the prediction, only 6% of students earned full credit by providing more than the obvious comment that their ‘RC  d2 values are different.’ In the 2019 paper the students were told that the sealed source depicted emitted three types of radiation. This meant that for α and β radiation the source could be thought of as directional. Later in that question, an aluminium absorber was placed in front of the open end of the source so that only γ radiation could be detected. However this radiation is emitted in all directions regardless of which way the open end of the source is pointing. It seemed that in the 2021 paper many students overlooked this when answering question 01.4. We expected them to state that the detector would be moved towards the source (about 40% did), but less than 15% explained that this maximised the distance between themselves and the source. This question discriminated in favour of those with direct experience of using a sealed source. In question 01.6, only 30% of students gave the analysis (log RC = −2 log d + log k) that was the gateway to further progress in this straightforward question. In question 01.8, about 40% referred to the random nature of radioactive decay, scoring the first mark, although some thought that the question concerned exponential decay. Some of the attempts to explain why all 100 photons would not be detected were tortuous to read.

  Text version

  A sealed gamma source has its open end 138 mm above a bench. A detector is clamped vertically above it to test the inverse-square law.

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• AQA 7408 · November 2020 · Paper 2 · Q5 · 10 marks

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  [05.2] Very few students answered this correctly. Most scripts showed an arrow either in a vague upward direction (possibly normal to the path) or an arrow pointed tangentially along the path. It was clear that most students did not connect ‘rate of change of momentum’ with a force.

  Text version

  Parallel alpha particles approach a gold-197 nucleus from the left at equal speed. Path 1 passes above the nucleus and curves upward. Particles 2 and 3 start progressively closer above the nucleus; particle 4 is aimed through its centre; particles 5-9 pass below at progressively larger impact parameters.

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• AQA 7408 · June 2018 · Paper 2 · Q5 · 6 marks

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  [05.2] It was clear that over 90% of students were not aware of how materials can become radioactive. There were extremely few references to nuclei. Students mainly wrote that the induced radioactivity was “too small to be of harm” or “has a short half-life” or “is only ionised a bit, so can be ignored”.

  Text version

  Metal surgical instruments are radiation-sterilised. A G-M source experiment gives background-corrected counts/min9013,1395,242 at distances0.20,0.50,1.00m.

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• AQA 7408 · June 2018 · Paper 2 · Q6 · 10 marks

  10 marks

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  [06.2] 62.4% of students found this to be an accessible question and gained the mark. The ‘near- miss’ answer put forward by many others was to write about increasing the volume of the cylindrical tube. The problem here is that it was not made clear that the height and not the diameter occupied by the water needs to be altered.

  Text version

  Radioactive decay is modelled by water draining from cylindrical tube with flow rate proportional to depth. Initial depth16.0cm and graph half-depth time19s. Rb-87 decay constant1.42 x10^-11 year^-1; Moon rock age4.47 x10^9y and current Rb-87 mass1.23mg.

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• AQA 7408 · June 2017 · Paper 2 · Q4 · 11 marks

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  [04.4] It was clear that the vast majority of students did not have knowledge about nuclear waste management. Many just expanded on their reasonably sensible thoughts of ‘keep clear from it, and get rid of it’. For weaker students, this simply meant wearing protective clothing and sending the waste into space. The middle-ability students gave a better solution by suggesting handling the waste remotely, encasing the waste in a named and effective radiation shield, and placing it in a deep mine or trench away from people. It was only about 20% of students who seemed to write with knowledgeable authority. These students knew it was the spent fuel rods that posed the main problem, unlike others who could answer with any item that had to do with the reactor. It was also only these students that knew about waste producing heat or about vitrification. It was rare for any student to refer to reprocessing. In terms of the quality of the writing, it was clear that most students do not give themselves even a brief plan. Often the ideas presented did not follow a logical sequence.

  Text version

  A thermal nuclear reactor uses a moderator, control rods and uranium fuel, and produces high-level radioactive waste.

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• AQA 7408 · June 2017 · Paper 2 · Q5 · 9 marks

  9 marks

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  [05.2] A majority of students understood the situation and performed the calculation without error. A significant number of others missed seeing the longest energy gap between iron and cobalt. Many of these gave a variety of calculations using energy gaps that did not correspond to beta energies.

  Text version

  Cobalt-59 has nuclear mass 58.93320 u. Iron-59 beta-minus decays with total available energy 2.52 x 10^-13 J to excited cobalt-59 levels at 2.29, 2.06 and 1.76 x 10^-13 J above the ground state. Proton mass 1.00728 u and neutron mass 1.00867 u.

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