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Original questions in the style of each exam boardEvery answer re-solved independently before publishingCreated by Evan Kotronis with AI assistanceUpdated 15 October 2026 · new questions added continuouslyFree access until 30 November 2026How every question is checked →
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1IGPC-039-00-01Atomic structure, isotopes, fission and fusionPaper CEasy1 mark
A sodium nucleus is represented as 2311Na. How many neutrons are in this nucleus?
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The nucleon number (23) is the total number of protons and neutrons. The proton number is 11, so the number of neutrons is 23 − 11 = 12. Option 11 is the proton number, 23 is the nucleon number, and 34 comes from adding the two numbers instead of subtracting.
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Answer B
Answer: B
Exam tip: Top number = protons + neutrons. Bottom number = protons. Neutrons = top − bottom.
2IGPC-039-00-02Atomic structure, isotopes, fission and fusionPaper CEasy1 mark
Which statement about two isotopes of the same element is correct?
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Isotopes are atoms of the same element, so they have the same proton number. They differ only in the number of neutrons, so their nucleon numbers are different. Their neutral atoms have equal numbers of electrons because the number of electrons equals the number of protons.
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Answer C
Answer: C
Common error: Swapping protons and neutrons in the definition. The number of protons decides which element an atom is, so it cannot change between isotopes.
3IGPC-039-00-03Atomic structure, isotopes, fission and fusionPaper CEasy1 mark
A neutral atom loses one electron. What is formed?
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After losing a negative electron, the atom has one more proton than electrons. It now has an overall positive charge, so it is a positive ion. The nucleus is unchanged, so the element and the isotope stay the same.
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Answer B
Answer: B
Common error: Thinking that losing an electron makes the atom negative. Losing negative charge leaves the particle positive.
4IGPC-039-00-07Atomic structure, isotopes, fission and fusionPaper CEasy1 mark
Which statement describes nuclear fusion?
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Fusion is the joining of two light nuclei to form a heavier nucleus, and energy is released. This is the energy source of stars. Splitting a large nucleus is fission. Emitting an alpha particle is radioactive decay.
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Answer B
Answer: B
Exam tip: Fusion joins nuclei together; fission splits a nucleus apart. Both release energy.
5IGPC-039-00-08Atomic structure, isotopes, fission and fusionPaper CEasy1 mark
What is meant by the nucleon number of a nucleus?
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Nucleons are the particles found in the nucleus, which are protons and neutrons. The nucleon number is their total. The number of protons alone is the proton number. Electrons are outside the nucleus, so they are not nucleons.
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Answer C
Answer: C
Common error: Including electrons in the nucleon number. Electrons are not in the nucleus.
6IGPC-039-00-11Atomic structure, isotopes, fission and fusionPaper CEasy5 marks
A lithium atom is represented as 73Li.
(a)
Name the two types of particle found in the nucleus.
(1)
(b)
State the number of protons and the number of neutrons in this nucleus.
(2)
(c)
The neutral lithium atom gains one electron. State the name of the particle formed and the sign of its overall charge.
(2)
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Part (a)
protons and neutrons (both needed)
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Part (b)
protons = 3 ; neutrons = 7 − 3 = 4
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Part (c)
an ion ; negative charge
✓ 2
Common error: Giving 7 as the number of neutrons. The nucleon number includes the protons, so subtract the proton number.
7IGPC-039-01-01Radioactivity, half-life and safetyPaper CEasy1 mark
Which type of radiation produces the most ionisation as it passes through air?
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α-particles are relatively heavy and carry a charge of +2. They interact strongly with air molecules and lose their energy over a few centimetres, so they produce the most ionisation. γ-rays are the most penetrating, but they are the least ionising. β-particles lie between the two.
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Answer A
Answer: A
Common error: Penetrating ability and ionising ability are linked the opposite way round. The most ionising radiation (α) is the least penetrating.
8IGPC-039-01-02Radioactivity, half-life and safetyPaper CEasy1 mark
A radioactive source emits only one type of radiation. The radiation passes through a sheet of paper. It is stopped by a sheet of aluminium 5 mm thick. Which type of radiation does the source emit?
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β-particles pass through paper but are absorbed by a few millimetres of aluminium. α-particles would be stopped by the paper. γ-rays would pass through 5 mm of aluminium with little reduction and need thick lead or concrete to absorb them. X-rays are not emitted by a radioactive nucleus and also penetrate aluminium.
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Answer B
Answer: B
Exam tip: Learn the three absorbers: paper stops α, a few mm of aluminium stops β, and thick lead only reduces γ.
9IGPC-039-01-03Radioactivity, half-life and safetyPaper CEasy1 mark
The corrected count rate from a radioactive sample is 640 counts/min. The half-life of the isotope is 3.0 hours. What is the corrected count rate after 9.0 hours?
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9.0 hours is 9.0 ÷ 3.0 = 3 half-lives. The count rate halves three times: 640 → 320 → 160 → 80 counts/min. 213 counts/min comes from dividing by 3 instead of halving. 160 counts/min stops after two half-lives. 40 counts/min uses four half-lives.
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Answer B
Answer: B
Common error: Find the number of half-lives first, then halve that many times. Do not divide the count rate by the number of half-lives.
10IGPC-039-01-08Radioactivity, half-life and safetyPaper CEasy1 mark
A laboratory technician uses a source that emits γ-rays. Which action reduces her exposure to the radiation most effectively?
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γ-rays are very penetrating. Only dense, thick materials such as lead absorb a large fraction of them. A lead-lined box between the source and the technician (shielding) greatly reduces her exposure. Cardboard and paper have almost no effect on γ-rays. Temperature does not change the rate of radioactive decay.
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Answer B
Answer: B
Exam tip: The three ways to reduce exposure are: reduce the time spent near the source, increase the distance from it, and use suitable shielding.
11IGPC-039-01-12Radioactivity, half-life and safetyPaper CEasy4 marks
This question is about the three types of nuclear radiation.
(a)
State what an α-particle consists of.
(1)
(b)
State the charge on a γ-ray.
(1)
(c)
A student places different absorbers between a source and a detector. The background count rate is 22 counts/min. Her results are: no absorber: 250 counts/min sheet of paper: 248 counts/min 5 mm of aluminium: 22 counts/min Deduce which type or types of radiation the source emits. Explain your answer.
(2)
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Part (a)
two protons and two neutrons (a helium nucleus)
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Part (b)
zero / it is uncharged
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Part (c)
The source emits β-particles only . The paper causes almost no drop, so no α is emitted, and 5 mm of aluminium reduces the count to background, so no γ is emitted .
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Exam tip: Compare each reading with the background count rate. A reading equal to the background means no radiation from the source is getting through.
12IGPC-039-01-11Radioactivity, half-life and safetyPaper CEasy5 marks
A student uses a Geiger–Müller tube connected to a counter to investigate background radiation in a laboratory.
(a)
State two sources of background radiation.
(2)
(b)
With no source present, the student measures the count rate three times. She obtains 18, 22 and 20 counts/min. Explain why the readings are not all the same.
(1)
(c)
Calculate the mean background count rate.
(1)
(d)
A radioactive source is placed near the tube. The reading is now 164 counts/min. Calculate the count rate due to the source alone.
(1)
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Part (a)
Any two different sources from: radon gas in the air; rocks or building materials; cosmic rays; food or drink; medical sources (e.g. radioactive tracers); fallout from nuclear weapons tests or accidents.
—
First correct source
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Second, different correct source
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Part (b)
Radioactive decay is random (and spontaneous), so the number of decays detected in each minute varies
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Part (c)
(18 + 22 + 20) ÷ 3 = 20 counts/min
✓ 1
Part (d)
164 − 20 = 144 counts/min
✓ 1
Exam tip: A corrected count rate always means the measured count rate minus the background count rate.
13IGPC-039-00-12Atomic structure, isotopes, fission and fusionPaper CMedium5 marks
Chlorine has two common isotopes, 3517Cl and 3717Cl.
(a)
Explain what is meant by the term isotopes.
(2)
(b)
State the number of neutrons in each isotope.
(2)
(c)
A neutral atom of each isotope contains the same number of electrons. Suggest why.
(1)
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Part (a)
atoms (nuclei) of the same element / with the same number of protons ; with different numbers of neutrons / different nucleon numbers
both atoms have 17 protons, and a neutral atom has equal numbers of protons and electrons
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Exam tip: A full definition of isotopes needs two points: the same proton number and a different neutron number.
14IGPC-039-01-04Radioactivity, half-life and safetyPaper CMedium1 mark
A detector placed near a radioactive source gives a reading of 340 counts/min. The background count rate is 20 counts/min. The half-life of the source is 2 days. What reading does the detector give 4 days later?
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The corrected count rate is 340 − 20 = 320 counts/min. Four days is 2 half-lives, so the corrected count rate becomes 320 ÷ 4 = 80 counts/min. The detector also records the background, which does not decay, so it reads 80 + 20 = 100 counts/min. 85 counts/min comes from halving the uncorrected reading. 65 counts/min subtracts the background after halving the uncorrected reading. 80 counts/min forgets to add the background back on.
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Answer D
Answer: D
Exam tip: Background radiation does not halve. Subtract it before applying the half-life, then add it back if the question asks for what the detector actually reads.
15IGPC-039-01-09Radioactivity, half-life and safetyPaper CMedium1 mark
A factory produces paper sheet. A radioactive source on one side of the sheet and a detector on the other side are used to monitor its thickness continuously for many years. Which source is most suitable?
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β-particles are partly absorbed by paper. A small change in thickness therefore causes a measurable change in the count rate. A half-life of 30 years means the count rate stays nearly constant over the working life of the equipment. α-particles would be completely stopped by the paper. γ-rays would pass through almost unaffected, so changes in thickness could not be detected. A 5-minute half-life would make the count rate fall too quickly to be useful.
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Answer B
Answer: B
Exam tip: When choosing a source, justify both the type of radiation (how penetrating it is) and the half-life (how long it must last).
16IGPC-039-01-13Radioactivity, half-life and safetyPaper CMedium6 marks
A hospital uses a radioactive tracer to examine a patient's kidneys. The tracer emits only γ-rays and has a half-life of 6.0 hours. It is injected into the patient. A detector outside the body records the radiation.
(a)
Explain why a γ-emitter is suitable for this use.
(2)
(b)
Explain why a half-life of 6.0 hours is suitable.
(2)
(c)
The activity of the tracer at injection is 480 MBq. Calculate its activity 24 hours later.
(2)
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Part (a)
γ-rays are penetrating enough to pass out of the body and reach the detector ; they are weakly ionising, so they cause less damage to cells .
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Part (b)
It is long enough for the tracer to reach the kidneys and for the scan to be completed ; it is short enough that the activity in the patient falls to a low level quickly, which limits the dose .
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Part (c)
24 ÷ 6.0 = 4 half-lives
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480 ÷ 24 = 30 MBq
✓ 1
Exam tip: When you explain a choice of half-life, give both sides: why it is not too short and why it is not too long.
17IGPC-039-00-04Atomic structure, isotopes, fission and fusionPaper EMedium1 mark
An iron nucleus is represented as 5626Fe. What is the relative charge on this nucleus?
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Only protons in the nucleus are charged, and each has a relative charge of +1. Neutrons are uncharged. The nucleus contains 26 protons, so its relative charge is +26. The value +30 counts the neutrons instead, +56 counts every nucleon, and 0 is the charge of the whole neutral atom, not of the nucleus.
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Answer A
Answer: A
Exam tip: The relative charge of a nucleus equals the proton number. The relative mass is approximately equal to the nucleon number.
18IGPC-039-00-05Atomic structure, isotopes, fission and fusionPaper EMedium1 mark
In an alpha-particle scattering experiment, a beam of alpha particles is directed at a very thin gold foil. Almost all of the alpha particles pass straight through the foil with no deflection. What does this observation show?
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If almost all alpha particles meet nothing that affects them, the atom must be mostly empty space. The positive charge of the nucleus is shown by the few large deflections, not by the particles that pass straight through. The experiment gives no evidence about neutrons or electron shells.
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Answer B
Answer: B
Exam tip: Link each observation to its own conclusion. Straight through means mostly empty space. Large deflection means a small, dense, positive nucleus.
19IGPC-039-00-06Atomic structure, isotopes, fission and fusionPaper EMedium1 mark
A uranium-235 nucleus absorbs a neutron and undergoes fission: 23592U + 10n → 14054Xe + 94ZSr + 210n What is the value of Z?
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Proton numbers must balance on both sides of the equation. The left side has 92 + 0 = 92. Neutrons have a proton number of 0, so 92 = 54 + Z, which gives Z = 38. The value 40 wrongly counts the 2 neutrons as charged. The value 54 is xenon's proton number, and 94 is the nucleon number of strontium.
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Answer A
Answer: A
Common error: Giving the neutron a proton number of 1. A neutron has proton number 0, so it adds nothing to the bottom-row total.
20IGPC-039-00-14Atomic structure, isotopes, fission and fusionPaper EMedium7 marks
In a nuclear power station, one possible fission reaction is: 23592U + 10n → 14456Ba + 8936Kr + x10n
(a)
State what is meant by nuclear fission.
(1)
(b)
Calculate the value of x.
(2)
(c)
Explain how this reaction can lead to a chain reaction.
(2)
(d)
State how the total mass of the products compares with the total mass of the reactants, and state the main form of the energy released.
(2)
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Part (a)
the splitting of a large (heavy) nucleus into two smaller nuclei
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Part (b)
nucleon numbers balance: 235 + 1 = 144 + 89 + x ; x = 3
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Part (c)
each fission releases more than one neutron / releases 3 neutrons ; these neutrons are absorbed by other uranium-235 nuclei, causing further fissions
✓ 2
Part (d)
the total mass of the products is (slightly) less than that of the reactants ; energy is released mainly as kinetic energy of the products
✓ 2
Common error: Forgetting the incoming neutron on the left-hand side. The total nucleon number on the left is 236, not 235.
21IGPC-039-01-05Radioactivity, half-life and safetyPaper EMedium1 mark
The nuclide polonium-210, \({}^{210}_{84}\text{Po}\), decays by emitting an α-particle to form an isotope of lead (Pb). Which nuclide is formed?
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An α-particle is \({}^{4}_{2}\text{He}\). It carries away 4 nucleons and 2 protons. The nucleon number becomes 210 − 4 = 206 and the proton number becomes 84 − 2 = 82, giving \({}^{206}_{82}\text{Pb}\). \({}^{210}_{82}\text{Pb}\) changes only the proton number. \({}^{206}_{84}\text{Pb}\) changes only the nucleon number. \({}^{214}_{86}\text{Pb}\) adds the α-particle instead of removing it.
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Answer A
Answer: A
Exam tip: Check that the top numbers balance and the bottom numbers balance on both sides of a decay equation.
22IGPC-039-01-06Radioactivity, half-life and safetyPaper EMedium1 mark
A nucleus emits a β−-particle. What happens to the proton number and to the nucleon number of the nucleus?
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In β− decay, a neutron in the nucleus changes into a proton and a fast-moving electron, and the electron is emitted. The nucleus gains one proton and loses one neutron, so the proton number rises by 1. The total number of nucleons stays the same. The first option treats the emitted electron as if it removes a proton. The other options wrongly assume the nucleon number changes.
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Answer B
Answer: B
Common error: Losing a negative particle does not lower the proton number. A neutron turns into a proton, so the proton number goes up.
23IGPC-039-01-07Radioactivity, half-life and safetyPaper EMedium1 mark
A narrow beam containing α-particles, β-particles and γ-rays passes between two parallel charged metal plates in a vacuum. Which statement describes what happens?
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α-particles are positive and β-particles are negative, so the electric field deflects them in opposite directions. A β-particle has a much smaller mass than an α-particle, so it is deflected much more, even though its charge is only half as large. γ-rays are uncharged and pass straight through. The last option assumes the larger charge of the α-particle gives the larger deflection, ignoring its much greater mass.
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Answer C
Answer: C
Exam tip: Deflection depends on both charge and mass. β-particles are thousands of times lighter than α-particles, so they bend far more.
24IGPC-039-01-14Radioactivity, half-life and safetyPaper EMedium6 marks
Strontium-90, \({}^{90}_{38}\text{Sr}\), decays by β− emission to form yttrium (Y). The half-life of strontium-90 is 29 years.
(a)
Write the nuclide notation for the isotope of yttrium formed.
(2)
(b)
Describe the change that occurs inside the nucleus during β− decay.
(1)
(c)
The yttrium nucleus also decays by β− emission to form zirconium (Zr). State the nucleon number and the proton number of the zirconium nucleus.
(1)
(d)
Calculate the time taken for the activity of a sample of strontium-90 to fall to \(\frac{1}{8}\) of its initial value.
(2)
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Part (a)
nucleon number 90
✓ 1
proton number 39, giving \({}^{90}_{39}\text{Y}\)
✓ 1
Part (b)
A neutron changes into a proton and an electron, and the electron is emitted .
✓ 1
Part (c)
nucleon number 90 and proton number 40
✓ 1
Part (d)
\(\frac{1}{8} = \left(\frac{1}{2}\right)^3\), so 3 half-lives
✓ 1
3 × 29 = 87 years
✓ 1
Common error: In β⁻ decay the nucleon number stays the same. Do not subtract 1 from it because an electron leaves.
25IGPC-039-00-13Atomic structure, isotopes, fission and fusionPaper EMedium7 marks
In a vacuum, a narrow beam of alpha particles is directed at a gold foil that is only a few hundred atoms thick. Detectors placed around the foil record the directions in which the alpha particles travel after they hit the foil.
(a)
Describe what is observed about the paths of the alpha particles.
(3)
(b)
Explain what these observations show about the structure of the atom.
(4)
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Part (a)
most alpha particles pass straight through the foil undeflected ; a small number are deflected through small angles ; a very small number are deflected through large angles / bounce back towards the source
✓ 3
Part (b)
most of the atom is empty space, because most alpha particles pass straight through ; the nucleus is positively charged, because it repels / deflects the positive alpha particles ; the nucleus is very small compared with the atom, because very few alpha particles are deflected through large angles ; the nucleus contains most of the mass of the atom / is very dense, because some alpha particles bounce back
✓ 4
Exam tip: In part (b), state each conclusion separately. Link each one to the specific observation from part (a) that provides the evidence for it.
26IGPC-039-00-10Atomic structure, isotopes, fission and fusionPaper EMedium1 mark
Two hydrogen nuclei fuse: 21H + 31H → 42He + X What is particle X?
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Nucleon numbers: 2 + 3 = 4 + A, so A = 1. Proton numbers: 1 + 1 = 2 + Z, so Z = 0. A particle with nucleon number 1 and proton number 0 is a neutron. A proton would need Z = 1. An electron has A = 0 and Z = −1. An alpha particle has A = 4 and Z = 2.
✓ 1
Answer B
Answer: B
Exam tip: Balance the top and bottom rows separately, then match the leftover numbers to a particle.
27IGPC-039-00-09Atomic structure, isotopes, fission and fusionPaper EHard1 mark
Three nuclei are described below. Nucleus P: proton number 17, nucleon number 35 Nucleus Q: 17 protons and 20 neutrons Nucleus R: 18 protons and 17 neutrons Which statement is correct?
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P has 17 protons, and Q also has 17 protons, so they are the same element. Q has nucleon number 37 and P has 35, so P and Q are isotopes with the same relative charge (+17) but different relative masses. R has 18 protons, so it is a different element. R has the same nucleon number as P (35), but a different relative charge (+18).
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Answer A
Answer: A
Exam tip: Work out the proton number and nucleon number of every nucleus before comparing them. Isotopes share the proton number, not the nucleon number.
28IGPC-039-00-16Atomic structure, isotopes, fission and fusionPaper EHard7 marks
An iron nucleus is represented as 5626Fe. The charge on a proton is 1.6×10−19 C. The mass of a single proton or neutron is about 1.67×10−27 kg.
(a)
State the number of neutrons in this nucleus.
(1)
(b)
Calculate the charge on the nucleus.
(2)
(c)
Calculate the approximate mass of the nucleus.
(2)
(d)
Another isotope of iron is 5426Fe. State how the charge and the mass of its nucleus compare with those of 5626Fe.
(2)
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Part (a)
56 − 26 = 30
✓ 1
Part (b)
charge = 26 × 1.6×10−19 ; = 4.2×10−18 C
✓ 2
Part (c)
mass = 56 × 1.67×10−27 ; = 9.4×10−26 kg
✓ 2
Part (d)
the charge is the same, because it has the same number of protons (26) ; the mass is smaller, because it has 2 fewer neutrons
✓ 2
Common error: Using the nucleon number to work out the charge. Only protons are charged, so multiply the proton number by the proton charge.
29IGPC-039-01-10Radioactivity, half-life and safetyPaper EHard1 mark
A detector near a radioactive sample reads 430 counts/min. Twenty-four minutes later it reads 80 counts/min. The background count rate throughout is 30 counts/min. What is the half-life of the sample?
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Subtract the background from both readings. The corrected count rates are 430 − 30 = 400 counts/min and 80 − 30 = 50 counts/min. 400 → 200 → 100 → 50 is 3 half-lives. These take 24 min, so the half-life is 24 ÷ 3 = 8 min. Using the uncorrected readings (430 → 80) gives about 2.4 halvings and a half-life of about 10 min. 12 min assumes only two half-lives. 6 min comes from miscounting four halvings.
✓ 1
Answer B
Answer: B
Common error: Subtract the background from every reading before counting halvings. Uncorrected readings never halve cleanly.
30IGPC-039-01-15Radioactivity, half-life and safetyPaper EHard8 marks
A student measures the count rate near a radioactive sample every 2.0 minutes. The background count rate in the room is 40 counts/min. Her measured count rates are: t = 0 min: 1240 counts/min t = 2.0 min: 796 counts/min t = 4.0 min: 516 counts/min t = 6.0 min: 340 counts/min t = 8.0 min: 229 counts/min
(a)
Explain why the readings must be corrected before the half-life is found.
(1)
(b)
Calculate the corrected count rates at t = 0 and at t = 6.0 min.
(2)
(c)
Use your corrected count rates at t = 0 and t = 6.0 min to determine the half-life of the sample.
(2)
(d)
Predict the reading on the detector at t = 12.0 min.
(3)
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Part (a)
The detector also records background radiation, which does not come from the sample (and does not decay), so it must be subtracted to give the count rate from the sample alone .
✓ 1
Part (b)
1240 − 40 = 1200 counts/min
✓ 1
340 − 40 = 300 counts/min
✓ 1
Part (c)
1200 → 600 → 300 is 2 half-lives
✓ 1
half-life = 6.0 ÷ 2 = 3.0 min
✓ 1
Part (d)
12.0 min is 4 half-lives
✓ 1
corrected count rate = 1200 ÷ 16 = 75 counts/min
✓ 1
reading = 75 + 40 = 115 counts/min
✓ 1
Exam tip: If the question asks what the detector reads, add the background back on after applying the half-life.
31IGPC-039-00-15Atomic structure, isotopes, fission and fusionPaper EHard6 marks
In some fusion reactions, deuterium nuclei join together: 21H + 21H → 32He + X
(a)
Identify particle X. Give its nucleon number and proton number.
(2)
(b)
Fusion happens only at extremely high temperatures, such as inside stars. Explain why.
(3)
(c)
State one difference between fusion and fission, other than the temperature needed.
(1)
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Part (a)
a neutron ; nucleon number 1 and proton number 0
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Part (b)
the nuclei are both positively charged, so there is electrostatic repulsion between them ; at high temperature the nuclei have very high kinetic energy / speed ; this lets them overcome the repulsion and get close enough to join / fuse, held by the strong nuclear force
✓ 3
Part (c)
any one valid difference, e.g. fusion joins light nuclei whereas fission splits a heavy nucleus / fission is started by a nucleus absorbing a neutron but fusion is not / fission products are highly radioactive but fusion products are mainly not / fusion releases more energy per unit mass of fuel
✓ 1
Exam tip: For 'explain' questions about fusion, name the force involved: electrostatic repulsion between positive nuclei.
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