References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
or see the official Cambridge past-papers page; for other papers, ask your
school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Radioactivity · Core · Paper 4 style · 7 marks
(a)Compare alpha, beta and gamma emissions. For each, state its nature, its relative charge and what is needed to stop most of it.[6]
(b)State which of the three is the most strongly ionising.[1]
Show answer
(a) alpha: helium nucleus (2 protons + 2 neutrons), charge +2, stopped by a sheet of paper (or a few cm of air); beta: high-speed electron, charge −1, stopped by a few mm of aluminium; gamma: electromagnetic radiation, no charge, reduced significantly only by several cm of lead or thick concrete
For each emission: nature and charge both correct (B1); absorber correct (B1); 2 marks × 3 emissions = 6
(b) alpha
B1
Q2Radioactivity · Core · Paper 2 style · 1 mark
(a)Which type of radiation is the least penetrating but the most ionising?[1]
Show answer
(a) A alpha
Alpha particles are large and doubly charged, so they ionise strongly and lose energy quickly, being stopped by paper. Gamma (C) is the most penetrating and least ionising.
Q3Radioactivity · Core · Paper 4 style · 5 marks
(a)State three ways in which a laboratory worker can reduce the dose received from a radioactive source.[3]
(b)Explain why an alpha source is particularly dangerous if it is swallowed or breathed in, even though it is easily stopped outside the body.[2]
Show answer
(a) reduce the time of exposure; increase the distance from the source (use tongs); use shielding (lead screen / store in lead box)
1 mark each
(b) inside the body all the alpha particles are absorbed by nearby cells; alpha is highly ionising, so it causes severe local damage to cells (mutation, cancer)
absorbed by tissue inside body (B1); strongly ionising damages cells (B1)
Q4Radioactivity · Core · Paper 4 style · 5 marks
(a)Explain what is meant by radioactive decay.[2]
(b)Radioactive decay is described as random and spontaneous. Explain what these two words mean.[2]
(c)Describe what is meant by ionisation.[1]
Show answer
(a) a change in an unstable nucleus that results in the emission of alpha particles, beta particles or gamma radiation
unstable nucleus (B1); emits α, β or γ (B1)
(b) random: it is not possible to predict which nucleus will decay next or when; spontaneous: decay is not affected by external conditions such as temperature or pressure
B1 each
(c) the removal (or addition) of electrons from atoms, making them charged ions
B1
Q5Radioactivity · Core · Paper 4 style · 4 marks
A radioactive source has a count rate of 640 counts/min (corrected for background). After 10 minutes the corrected count rate is 160 counts/min.
(a)Calculate the half-life of the source.[2]
(b)Predict the corrected count rate after a further 10 minutes.[1]
(c)The source is warmed to 60 °C. State the effect on the half-life.[1]
Show answer
(a) 5.0 minutes
640 → 320 → 160 is two half-lives (C1); 10 ÷ 2 = 5.0 min (A1)
(b) 40 counts/min
two more half-lives: 160 → 80 → 40 (B1)
(c) no effect; half-life is not affected by temperature
B1
Q6Radioactivity · Standard · Paper 4 style · 5 marks
Iodine-131 is used in hospitals to treat thyroid conditions. It has a half-life of 8.0 days. A sample has an activity of 1600 Bq.
(a)Define half-life.[1]
(b)Calculate the activity of the sample after 24 days.[2]
(c)Calculate the fraction of the original iodine-131 nuclei that remain after 40 days.[2]
Show answer
(a) the time taken for half the nuclei of a radioactive isotope in a sample to decay (or for the activity to halve)
Q7Radioactivity · Standard · Paper 4 style · 5 marks
A student uses a Geiger–Müller tube and counter in a school laboratory in Quetta.
(a)With no radioactive source present, the counter still records about 25 counts per minute. Name this radiation and state two of its sources.[3]
(b)With a source placed in front of the tube, the counter records 340 counts per minute. Calculate the count rate due to the source alone.[1]
(c)The count rate fluctuates from minute to minute even though the source does not change. Explain why.[1]
Show answer
(a) background radiation; sources: radon gas from the ground and buildings, rocks, cosmic rays, food and drink, medical sources
background radiation (B1); 1 mark each for any two sources
(b) 315 counts per minute
340 − 25 = 315 (B1)
(c) radioactive decay is random, so the number of decays in each minute varies
B1
Q8Radioactivity · Standard · Paper 4 style · 5 marks
(a)Radium-226 (²²⁶₈₈Ra) decays by emitting an alpha particle to form radon (Rn). Write the nuclide notation for the radon nucleus formed and the full decay equation.[2]
(b)Carbon-14 (¹⁴₆C) decays by beta emission to form nitrogen (N). Write the decay equation.[2]
(c)Describe the change that takes place inside the nucleus during beta decay.[1]
Show answer
(a) ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He (α)
²²²₈₆Rn (B1); complete balanced equation with ⁴₂He (B1)
(b) ¹⁴₆C → ¹⁴₇N + ⁰₋₁e (β)
¹⁴₇N (B1); ⁰₋₁e / β shown (B1)
(c) a neutron changes into a proton and a (high-speed) electron, which is emitted
B1
Q9Radioactivity · Standard · Paper 2 style · 1 mark
(a)[1]
Show answer
(a) C both unchanged
Gamma radiation is electromagnetic radiation with no mass or charge, so the nucleus loses only energy. A describes alpha decay and B describes beta decay.
Q10Radioactivity · Standard · Paper 4 style · 6 marks
A paper mill in Faisalabad uses a radioactive source and a detector to monitor the thickness of the paper produced. The paper passes between the source and the detector.
(a)State which type of radiation should be used and explain why the other two are unsuitable.[3]
(b)The detector's count rate decreases. State what this shows about the paper and how the rollers should be adjusted.[2]
(c)Suggest why a source with a long half-life is chosen.[1]
Show answer
(a) beta; alpha would be completely absorbed by the paper; gamma would pass through almost unchanged, so changes in thickness would not change the count rate
beta (B1); alpha absorbed (B1); gamma not affected by thickness (B1)
(b) the paper is becoming thicker; the rollers should press harder (move closer together)
B1 each
(c) its activity stays almost constant over the period of use, so changes in count rate are due only to changes in thickness, and it does not need frequent replacement
B1
Q11Radioactivity · Standard · Paper 6 style · 7 marks
A teacher investigates the radiation from a sealed source, using a Geiger–Müller tube placed 3 cm from it. The background count rate is 32 counts/min.absorber: none — count rate 412 counts/minabsorber: thin paper — 405 counts/minabsorber: 3 mm aluminium — 36 counts/minabsorber: 10 mm lead — 34 counts/min
(a)Calculate the corrected count rate for each absorber.[2]
(b)Deduce which type or types of radiation the source emits. Explain your answer using the results.[3]
(c)State two safety precautions the teacher takes when handling the source.[2]
Show answer
(a) 380, 373, 4, 2 counts/min
subtract 32 from each; 2 marks all correct, 1 mark for two or three correct
(b) beta only: paper hardly reduces the count, so there is no significant alpha; 3 mm aluminium reduces the count almost to background, so it is beta; the count with aluminium is almost background, so there is no significant gamma
no alpha + reason (B1); beta + reason (B1); no gamma + reason (B1)
(c) handle it with long tongs; keep it as far from the body as possible; minimise the time it is out of its lead-lined box; never point it at anyone; return it to its box immediately after use
1 mark each for any two
Q12Radioactivity · Standard · Paper 4 style · 6 marks
Technetium-99m is a gamma emitter with a half-life of 6.0 hours. It is used as a medical tracer. A patient is injected at 08:00 with a dose of activity 400 MBq.
(a)Calculate the activity in the patient at 20:00 on the same day, ignoring any removal from the body.[2]
(b)Calculate the time on the clock when the activity has fallen to 25 MBq.[2]
(c)Explain two reasons why technetium-99m is suitable as a medical tracer.[2]
400 → 25 is 4 half-lives = 24 h (C1); 08:00 next day (A1)
(c) it emits gamma rays, which pass out of the body to be detected outside and are only weakly ionising; its short half-life means the activity in the body falls quickly, reducing the patient's dose, but is long enough to complete the scan
gamma reason (B1); half-life reason (B1)
Q13Radioactivity · Standard · Paper 2 style · 1 mark
(a)The count rate from a radioactive sample falls from 3200 counts/min to 400 counts/min in 36 hours, after correcting for background. What is the half-life of the sample?[1]
Show answer
(a) C 12 hours
3200 → 1600 → 800 → 400 is three half-lives, so half-life = 36 ÷ 3 = 12 hours. A divides 36 by 8 (the ratio) instead of by the number of half-lives.
Q14Radioactivity · Standard · Paper 5 style · 6 marks
In a class model of radioactive decay, a student starts with 600 dice. Each 'throw', she throws all remaining dice and removes every die showing a six. She records the number of dice remaining after each throw.throw number: 0, 1, 2, 3, 4, 5, 6dice remaining: 600, 500, 417, 347, 289, 241, 201
(a)State what one die and one throw represent in the model.[2]
(b)Use the results to estimate the 'half-life' of the dice in throws.[2]
(c)Explain how the model shows that radioactive decay is random.[1]
(d)Suggest why using 6000 dice would give results that fit a smooth curve more closely.[1]
Show answer
(a) one die represents an unstable nucleus; one throw represents a fixed interval of time
B1 each
(b) about 3.8 throws (accept 3.5–4.0)
300 dice remaining lies between throw 3 (347) and throw 4 (289) (C1); about 3.8 throws (A1)
(c) it is impossible to predict which die will show a six on any throw, but the number removed each throw is a roughly constant fraction (about 1/6) of those remaining
B1
(d) with larger numbers the random variations are a smaller fraction of the total
B1
Q15Radioactivity · Standard · Paper 4 style · 5 marks
In radiotherapy at a cancer hospital, beams of gamma radiation are directed at a tumour from several different directions, all passing through the tumour.
(a)Explain why gamma radiation, and not alpha or beta radiation, is used for a tumour deep inside the body.[2]
(b)Explain why the beams are aimed from several directions rather than using one strong beam.[2]
(c)State why ionising radiation can kill cancer cells.[1]
Show answer
(a) gamma is the most penetrating, so it can pass through healthy tissue to reach the tumour; alpha and beta would be absorbed near the surface
B1 each point
(b) the tumour receives the dose from every beam, so it gets a large total dose; each region of healthy tissue is crossed by only one beam and receives a smaller dose, reducing damage
tumour gets combined dose (B1); healthy tissue gets less (B1)
(c) ionisation damages the DNA/cells so that they die or cannot divide
B1
Q16Radioactivity · Challenge · Paper 4 style · 7 marks
A student measures the count rate from a radioactive source every 2.0 minutes. The background count rate is 30 counts/min.time / min: 0, 2.0, 4.0, 6.0, 8.0, 10.0measured count rate / counts per min: 830, 534, 347, 230, 156, 109
(a)Calculate the corrected count rate due to the source at 0 min and at 6.0 min.[2]
(b)Use your answers to (a) to determine the half-life of the source.[2]
(c)Predict the measured count rate (including background) at 12.0 min.[2]
(d)Explain why it is important to correct for background radiation in this experiment.[1]
(d) background is a significant fraction of the low later readings; without correction the half-life found would be too long
B1
Q17Radioactivity · Challenge · Paper 4 style · 5 marks
Carbon-14 has a half-life of 5700 years. Living wood has a constant carbon-14 activity per gram.
(a)A piece of charcoal from a prehistoric hearth found in a cave has 1/8 of the carbon-14 activity per gram of living wood. Estimate its age.[2]
(b)A second sample has 25 % of the activity per gram of living wood. Estimate its age.[1]
(c)Suggest why carbon-14 dating cannot give a reliable age for an object about 100 years old.[2]
Show answer
(a) 17 100 years
1/8 = three half-lives (C1); 3 × 5700 = 17 100 years (A1)
(b) 11 400 years
two half-lives: 2 × 5700 = 11 400 years (B1)
(c) 100 years is very short compared with the half-life, so the activity has fallen by only a tiny fraction; this small change is hard to measure against the random variation in counts
tiny change in activity (B1); random fluctuations/background make it unmeasurable (B1)
Q18Radioactivity · Challenge · Paper 2 style · 1 mark
(a)[1]
Show answer
(a) C 7/8
After three half-lives (½)³ = 1/8 of the nuclei remain, so 1 − 1/8 = 7/8 have decayed. A is the fraction remaining, not the fraction decayed.
Q19Radioactivity · Challenge · Paper 4 style · 6 marks
Beams of alpha, beta and gamma radiation pass, one at a time, between two parallel metal plates. The upper plate is positive and the lower plate is negative.
(a)Describe the path of each type of radiation between the plates.[3]
(b)Explain why beta particles are deflected much more than alpha particles.[2]
(c)The plates are replaced by a magnetic field at right angles to the beams. State how the deflections of alpha and beta compare with each other.[1]
Show answer
(a) alpha: deflected towards the negative (lower) plate; beta: deflected towards the positive (upper) plate; gamma: not deflected
1 mark each
(b) beta particles have a much smaller mass than alpha particles (and a smaller, but comparable, charge), so the electric force gives them a much greater acceleration
beta has much smaller mass (B1); so larger deflection/acceleration for similar force (B1)
(c) they are deflected in opposite directions (beta much more strongly); gamma is still undeflected
B1
Q20Radioactivity · Challenge · Paper 4 style · 5 marks
Uranium-238 (²³⁸₉₂U) decays in three steps: first by alpha emission to thorium (Th), then by beta emission to protactinium (Pa), then by another beta emission to a nuclide Q.
(a)Write the nuclide notation for the thorium nucleus.[1]
(b)Determine the proton number and nucleon number of Q.[2]
(c)Identify Q and state its relationship to the original nucleus.[2]
Show answer
(a) ²³⁴₉₀Th
B1
(b) proton number 92, nucleon number 234
Pa is ²³⁴₉₁Pa (C1); Q is ²³⁴₉₂ (A1)
(c) Q is uranium-234; it is an isotope of uranium-238 (same proton number, 4 fewer neutrons)
uranium (B1); isotope / same proton number different nucleon number (B1)
Q21Radioactivity · Challenge · Paper 6 style · 7 marks
A student is given readings of the corrected count rate from a sample of radon-220 gas, measured every 20 s.time / s: 0, 20, 40, 60, 80, 100, 120corrected count rate / counts per s: 500, 390, 305, 238, 186, 145, 113
(a)Describe how to use a graph of these results to find the half-life.[2]
(b)From the readings, estimate the half-life of radon-220. Explain how you obtained your estimate.[2]
(c)Use your half-life to estimate the time at which the corrected count rate would be 62.5 counts/s.[2]
(d)Explain why the readings do not lie exactly on a smooth curve.[1]
Show answer
(a) plot count rate (y) against time (x) and draw a smooth curve of best fit; read the time at which the count rate is 250 counts/s (half the initial value); this time is the half-life
smooth curve through points (B1); read time for count rate to halve (B1)
(b) about 56 s (accept 54–58 s): 250 counts/s lies between 238 at 60 s and 305 at 40 s, close to 60 s
250 between 40 s and 60 s readings (C1); 56 s (A1)
(c) about 168 s (three half-lives)
500 → 62.5 is three half-lives (C1); 3 × 56 = 168 s (A1)
(d) radioactive decay is random, so the count in any interval fluctuates
B1
Q22Atom & nucleus (incl. fission/fusion) · Core · Paper 2 style · 1 mark
(a)[1]
Show answer
(a) B 143
neutrons = nucleon number − proton number = 235 − 92 = 143. A is the proton number; C the nucleon number.
Q23Atom & nucleus (incl. fission/fusion) · Core · Paper 4 style · 6 marks
(a)Describe the structure of an atom in terms of a nucleus and electrons.[2]
(b)State the relative charge of a proton, a neutron and an electron.[1]
(c)Explain what is meant by isotopes.[1]
(d)Carbon-12 is ¹²₆C and carbon-14 is ¹⁴₆C. State the number of protons and the number of neutrons in each nucleus.[2]
Show answer
(a) a small, positively charged nucleus containing protons and neutrons, surrounded by (negatively charged) electrons orbiting the nucleus
nucleus of protons and neutrons (B1); electrons orbit the nucleus (B1)
(b) proton +1, neutron 0, electron −1
B1 all three
(c) atoms (nuclides) of the same element with the same number of protons but different numbers of neutrons
Q24Atom & nucleus (incl. fission/fusion) · Core · Paper 4 style · 5 marks
A sodium atom is represented by ²³₁₁Na.
(a)State the number of protons and the number of neutrons in the nucleus.[2]
(b)State the number of electrons in a neutral sodium atom, and explain why the atom is neutral.[2]
(c)The atom loses one electron to form an ion. State the charge on the ion.[1]
Show answer
(a) 11 protons; 12 neutrons
B1 each
(b) 11 electrons; the number of negative electrons equals the number of positive protons, so the charges cancel
11 (B1); equal numbers of protons and electrons (B1)
(c) +1 (positive ion, Na⁺)
B1
Q25Atom & nucleus (incl. fission/fusion) · Standard · Paper 4 style · 6 marks
In the alpha-particle scattering experiment, a beam of alpha particles was directed at a very thin sheet of gold foil in a vacuum, and detectors recorded where the particles went.
(a)Describe the three main observations of the experiment.[3]
(b)Explain what each observation shows about the structure of the atom.[3]
Show answer
(a) most alpha particles passed straight through undeflected; a small number were deflected through small angles; a very small number were deflected through large angles (more than 90°), bouncing back
1 mark each
(b) most pass through: the atom is mostly empty space; some deflected: the nucleus is positively charged, repelling the positive alpha particles; very few bounce back: the nucleus is very small and contains most of the mass of the atom
1 mark each
Q26Atom & nucleus (incl. fission/fusion) · Standard · Paper 4 style · 5 marks
The Sun releases energy by nuclear fusion. A fusion reaction being tested for future power stations is:²₁H + ³₁H → ⁴₂He + X
(a)Identify particle X, giving its nucleon number and proton number.[2]
(b)Explain why fusion needs an extremely high temperature.[2]
(c)State one difference between fission and fusion.[1]
Show answer
(a) a neutron, ¹₀n
nucleon number 2 + 3 − 4 = 1 and proton number 1 + 1 − 2 = 0 (B1); neutron (B1)
(b) nuclei are positively charged and repel each other; at very high temperatures they move fast enough (have enough kinetic energy) to get close enough to fuse
repulsion of positive nuclei (B1); high speed / kinetic energy overcomes it (B1)
(c) fission splits a large nucleus into smaller ones; fusion joins two light nuclei to form a heavier one
B1
Q27Atom & nucleus (incl. fission/fusion) · Standard · Paper 2 style · 1 mark
(a)Two different isotopes of the same element always have the same[1]
Show answer
(a) C proton number
Isotopes are the same element, so the same number of protons, but different numbers of neutrons; so B (nucleon number) and D differ.
Q28Atom & nucleus (incl. fission/fusion) · Challenge · Paper 4 style · 6 marks
Pakistan's nuclear power stations at Chashma and Karachi use the fission of uranium-235 to generate electricity. One possible fission reaction is:²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + x ¹₀n
(a)Describe what happens in nuclear fission.[2]
(b)Determine the value of x and show that the proton numbers balance.[2]
(c)Explain how fission can lead to a chain reaction.[2]
Show answer
(a) a large, unstable nucleus absorbs a neutron and splits into two smaller daughter nuclei and two or three neutrons, releasing energy (mainly as kinetic energy of the products)
absorbs neutron and splits into two smaller nuclei (B1); neutrons and energy released (B1)
(c) the neutrons released can be absorbed by other uranium-235 nuclei, causing further fissions, which release more neutrons, and so on
neutrons from one fission (B1); cause further fissions (B1)
Q29Atom & nucleus (incl. fission/fusion) · Challenge · Paper 4 style · 6 marks
Four nuclides are labelled W, X, Y and Z.W: proton number 17, nucleon number 35X: proton number 17, nucleon number 37Y: proton number 18, nucleon number 37Z: proton number 19, nucleon number 40
(a)State which two nuclides are isotopes of the same element. Explain your choice.[2]
(b)State which two nuclides have the same nucleon number but are different elements.[1]
(c)Calculate the number of neutrons in each nuclide and state which has the most neutrons.[2]
(d)State the charge on the nucleus of Z in terms of the charge e on a proton.[1]
Show answer
(a) W and X: same proton number (17) but different nucleon numbers
W and X (B1); same proton number, different numbers of neutrons (B1)
(b) X and Y
B1
(c) W 18, X 20, Y 19, Z 21; Z has the most
all four correct (B1); Z (B1)
(d) +19e
B1
Q30Atom & nucleus (incl. fission/fusion) · Challenge · Paper 2 style · 1 mark
(a)In the alpha-particle scattering experiment, a very small fraction of alpha particles were deflected through angles greater than 90°. Which conclusion does this observation support?[1]
Show answer
(a) B Most of the mass and all the positive charge of an atom are in a very small nucleus.
Only a tiny, massive, positive nucleus could repel an alpha particle backwards, and its small size explains why this is rare. A is true but follows from the many undeflected particles, not from the back-scattering.
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
