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 2 style · 6 marks
(a)State the nature of (i) an alpha particle, (ii) a beta particle, (iii) gamma radiation.[3]
(b)State which of the three radiations is (i) the most ionising, (ii) the most penetrating.[2]
(c)State what is needed to stop most beta particles.[1]
Show answer
(a) (i) a helium nucleus (2 protons + 2 neutrons) (ii) a high-speed electron (from the nucleus) (iii) an electromagnetic wave
B1 each
(b) (i) alpha (ii) gamma
B1 each
(c) A few millimetres of aluminium
B1
Q2Radioactivity · Core · Paper 1 style · 1 mark
(a)Which type of radiation is stopped by a single sheet of paper?[1]
Show answer
(a) A alpha only
Alpha particles are highly ionising and have a very short range; paper absorbs them. Beta (B) needs a few mm of aluminium.
Q3Radioactivity · Core · Paper 2 style · 5 marks
(a)State what is meant by background radiation.[1]
(b)Give two natural sources and one man-made source of background radiation.[3]
(c)Suggest why the background count is higher in some regions than in others.[1]
Show answer
(a) Ionising radiation that is always present in the environment, from natural and artificial sources
B1
(b) Natural: radon gas from rocks/soil; rocks and building materials; cosmic rays; food and drink. Man-made: medical X-rays / treatments; nuclear power / fallout from weapons tests
B1 each, two natural and one man-made
(c) Different rocks (e.g. granite) contain more radioactive isotopes / more radon; higher altitude has more cosmic rays
B1
Q4Radioactivity · Core · Paper 2 style · 6 marks
(a)State three precautions a technician should take when handling a radioactive source in a school laboratory.[3]
(b)Explain why increasing the distance from a source reduces the risk.[1]
(c)Explain why ionising radiation is harmful to living cells.[2]
Show answer
(a) Use long-handled tongs; keep the source pointed away from people; minimise the time it is out; store it in a lead-lined box; wash hands after
1 mark each for any three
(b) Radiation spreads out and is absorbed by air, so less reaches the person (alpha and beta have short ranges in air)
B1
(c) It ionises atoms in cells, damaging molecules such as DNA; this can kill cells or cause mutations / cancer
B1 ionisation of molecules in cells; B1 cell death or mutation / cancer
Q5Radioactivity · Core · Paper 3 style · 3 marks
(a)A student uses a Geiger-Müller tube and counter with no source present. The counter records 30 counts in 2.0 minutes. Calculate the background count rate in counts/min.[1]
(b)A source is placed in front of the tube. The count rate is now 465 counts/min. Calculate the count rate due to the source alone.[1]
(c)Suggest why the student measures the background count for several minutes rather than a few seconds.[1]
Show answer
(a) 15 counts/min
30 ÷ 2.0 = 15 B1
(b) 450 counts/min
465 − 15 = 450 B1
(c) Decay is random, so a longer count gives a more reliable average
B1
Q6Radioactivity · Core · Paper 2 style · 5 marks
(a)Spent fuel from a nuclear power station contains radioactive isotopes. One of them, caesium-137, has a half-life of 30 years. Calculate how long it takes for its activity to fall to 1/32 of its starting value.[2]
(b)Suggest two precautions taken when storing such waste.[2]
(c)Give one advantage of nuclear power stations compared with gas-fired power stations.[1]
Show answer
(a) 150 years
1/32 = (½)⁵, so 5 half-lives M1; 5 × 30 = 150 years A1
(b) Sealed in thick steel/concrete or glass containers; stored deep underground or in shielded, secure sites away from water supplies; monitored
1 mark each for any two
(c) No carbon dioxide emitted while generating / large output from small fuel mass / reliable
B1
Q7Radioactivity · Standard · Paper 2 style · 4 marks
(a)Define the half-life of a radioactive isotope.[1]
(b)A sample has an activity of 1600 Bq. Its half-life is 6 hours. Calculate its activity after 24 hours.[2]
(c)Calculate how long it takes for the activity to fall to 200 Bq.[1]
Show answer
(a) The time taken for half the nuclei of the isotope in a sample to decay (or for the activity to halve)
Q8Radioactivity · Standard · Paper 2 style · 5 marks
(a)Radium-226, ²²⁶₈₈Ra, decays by emitting an alpha particle to form radon (Rn). Write the decay equation, showing the nucleon and proton numbers of the radon nucleus.[3]
(b)Radon is a gas. Explain why breathing in radon is more dangerous than being near a sealed source of radium outside the body.[2]
Show answer
(a) ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He (or α)
B1 alpha as ⁴₂He / ⁴₂α; B1 222; B1 86
(b) Alpha particles cannot penetrate skin, but inside the lungs they are emitted next to living cells; they are strongly ionising and damage cells / DNA
B1 alpha absorbed by dead skin layer outside body; B1 inside, strong ionisation of nearby cells
Q9Radioactivity · Standard · Paper 2 style · 6 marks
(a)Carbon-14, ¹⁴₆C, decays by beta emission to nitrogen. Write the decay equation.[3]
(b)Describe the change that takes place inside the nucleus during beta decay.[2]
(c)State why the nucleon number does not change in beta decay.[1]
Show answer
(a) ¹⁴₆C → ¹⁴₇N + ⁰₋₁e (or β)
B1 beta as ⁰₋₁e; B1 nucleon number 14; B1 proton number 7
(b) A neutron changes into a proton and an electron; the electron is emitted at high speed as the beta particle
B1 neutron → proton; B1 + electron emitted
(c) A neutron is replaced by a proton, so the total number of nucleons stays the same
B1
Q10Radioactivity · Standard · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) A proton number −2, nucleon number −4
An alpha particle contains 2 protons and 2 neutrons, so Z falls by 2 and A falls by 4. C describes beta decay.
Q11Radioactivity · Standard · Paper 2 style · 6 marks
(a)Technetium-99m is used as a medical tracer. It emits gamma radiation and has a half-life of 6.0 hours. Explain why a gamma emitter is chosen for a tracer that is injected into a patient.[2]
(b)Explain why a half-life of a few hours is suitable.[2]
(c)Calculate the fraction of the technetium-99m remaining 24 hours after injection.[2]
Show answer
(a) Gamma passes out of the body so it can be detected outside; it is weakly ionising so causes less damage
B1 penetrates tissue to reach the detector; B1 least ionising
(b) Long enough for the scan to be done; short enough that the activity soon falls, limiting the patient's dose
B1 long enough to detect; B1 decays quickly afterwards
(c) 1/16
24 ÷ 6.0 = 4 half-lives M1; (½)⁴ = 1/16 A1
Q12Radioactivity · Standard · Paper 1 style · 1 mark
(a)Which statement about radioactive decay is correct?[1]
Show answer
(a) A The decay of a nucleus is random and cannot be predicted.
Decay is random and spontaneous: it is not affected by temperature or pressure, and we can only predict what fraction of a large sample will decay. B is wrong: half-life is unaffected by physical conditions.
Q13Radioactivity · Standard · Paper 2 style · 5 marks
(a)A smoke detector contains a small source of americium-241, an alpha emitter. Alpha particles ionise the air between two plates, so a small current flows. Explain how smoke entering the detector sets off the alarm.[2]
(b)Explain why an alpha source is suitable for use in homes.[2]
(c)Americium-241 has a half-life of about 430 years. Explain why this is an advantage.[1]
Show answer
(a) Smoke particles absorb the alpha particles, so less air is ionised; the current falls and the circuit triggers the alarm
B1 smoke absorbs alpha / reduces ionisation; B1 current falls, which triggers the alarm
(b) Alpha is strongly ionising, so a small source gives a measurable current; alpha has a very short range and is stopped by the casing, so it is not a hazard outside the detector
B1 strongly ionising; B1 short range / stopped by casing
(c) The activity stays almost constant for the life of the detector, so it does not need replacing
B1
Q14Radioactivity · Standard · Paper 4 style · 5 marks
A Geiger-Müller tube is placed a short distance from a radioactive source. Different absorbers are placed between them. The background count rate is 20 counts/min.No absorber: 520 counts/minThin paper: 515 counts/min3 mm aluminium: 21 counts/min
(a)State the evidence that the source does not emit alpha particles.[1]
(b)State the evidence that the source emits beta particles.[1]
(c)State and explain whether the source emits gamma radiation.[2]
(d)Calculate the count rate due to the source when there is no absorber.[1]
Show answer
(a) Paper hardly reduces the count rate (520 → 515)
B1
(b) 3 mm of aluminium reduces the count rate greatly, but paper does not (515 → 21)
B1
(c) No: with 3 mm of aluminium the count rate (21 counts/min) is the same as the background (20 counts/min), so no radiation from the source passes through the aluminium
B1 no gamma; B1 aluminium reading equals background, but gamma would pass through 3 mm of aluminium almost unabsorbed
(d) 500 counts/min
520 − 20 = 500 B1
Q15Radioactivity · Standard · Paper 2 style · 5 marks
(a)Uranium-238, ²³⁸₉₂U, decays by alpha emission to thorium (Th). State the nucleon number and proton number of the thorium nucleus.[2]
(b)The thorium nucleus then decays by beta emission to protactinium (Pa). State the nucleon number and proton number of the protactinium nucleus.[2]
(c)After these two decays, the nucleus sometimes emits gamma radiation. State the effect of gamma emission on the nucleon number and proton number.[1]
Show answer
(a) nucleon number 234; proton number 90
B1 each
(b) nucleon number 234; proton number 91
B1 each
(c) No change to either
B1
Q16Radioactivity · Challenge · Paper 4 style · 7 marks
A student measures the count rate from a radioactive source with a Geiger-Müller tube and counter. The background count rate is 20 counts/min.Time / min: 0, 2, 4, 6, 8, 10Measured count rate / counts per min: 820, 586, 420, 303, 220, 161
(a)Explain why the background count rate must be subtracted from each reading.[1]
(b)Calculate the corrected count rate at 4.0 min and at 8.0 min.[2]
(c)Use your answers to find the half-life of the source.[1]
(d)Predict the count rate the student would measure at 12 minutes.[2]
(e)Explain why the readings do not follow a perfectly smooth curve when repeated.[1]
Show answer
(a) Background radiation is always present, so the measured rate includes counts not from the source
B1
(b) 400 counts/min; 200 counts/min
420 − 20 = 400 B1; 220 − 20 = 200 B1
(c) 4.0 minutes
corrected rate halves from 800 to 400 in 4.0 min (and 400 to 200 in the next 4.0 min) B1
(e) Radioactive decay is random (counts fluctuate)
B1
Q17Radioactivity · Challenge · Paper 2 style · 6 marks
(a)A factory makes thin aluminium foil. A radioactive source is placed on one side of the foil and a detector on the other, to monitor the thickness. State which type of radiation should be used. Explain why the other two types are unsuitable.[3]
(b)The count rate at the detector suddenly increases. State what has happened to the foil and what the control system should do.[2]
(c)Suggest whether the source should have a long or short half-life. Explain.[1]
Show answer
(a) Beta
B1 beta; B1 alpha would be completely stopped by the foil whatever its thickness; B1 gamma would pass through almost unchanged, so small thickness changes would not affect the count
(b) The foil has become thinner; the rollers should be moved apart (less pressure)
B1 thinner; B1 adjust rollers to increase thickness
(c) Long, so that the count rate does not fall noticeably during use (and the source need not be replaced often)
B1
Q18Radioactivity · Challenge · Paper 2 style · 6 marks
(a)Living wood contains carbon-14, which has a half-life of 5700 years. When a tree dies, the carbon-14 in it decays and is not replaced. A wooden bowl found at an archaeological site has a carbon-14 activity that is 1/8 of the activity of the same mass of living wood. Calculate the age of the bowl.[3]
(b)Another sample has 25 % of the activity of living wood. Calculate its age.[1]
(c)Suggest why carbon dating cannot be used for an object thought to be about 100 years old.[2]
(c) Very little of the carbon-14 has decayed in 100 years (much less than one half-life); the change in activity is too small to measure accurately against random fluctuations
B1 100 years is tiny compared with the half-life; B1 activity change too small to detect
Q19Radioactivity · Challenge · Paper 2 style · 6 marks
(a)A hospital receives 80 mg of iodine-131, which has a half-life of 8 days. Calculate the mass of iodine-131 remaining after 40 days.[2]
(b)Calculate the mass of iodine-131 that has decayed in this time.[1]
(c)The iodine-131 emits beta particles. State one reason why used waste from the hospital must be stored safely before disposal.[1]
(d)Find the smallest whole number of half-lives after which the mass of iodine-131 is less than 1.0 mg, and state this time in days.[2]
Show answer
(a) 2.5 mg
40 ÷ 8 = 5 half-lives M1; 80 ÷ 2⁵ = 2.5 mg A1
(b) 77.5 mg
80 − 2.5 = 77.5 mg B1
(c) It is still radioactive and its emissions can ionise and damage living cells; it must be stored until the activity is very low
(b) It kills bacteria / microorganisms by damaging their cells (ionisation)
B1
(c) Gamma rays do not change the nuclei of the atoms in the instruments; the instruments are irradiated, not contaminated (no radioactive material is left on them)
B1 nuclei unchanged; B1 difference between irradiation and contamination
(d) So the activity remains roughly constant and the source does not need frequent replacement
B1
Q21Atom & nucleus · Core · Paper 2 style · 5 marks
(a)A sodium nucleus is represented as ²³₁₁Na. State the proton number and the nucleon number of this nuclide.[2]
(b)Calculate the number of neutrons in the nucleus.[1]
(c)State the number of electrons in a neutral atom of sodium-23. Explain your answer.[2]
Show answer
(a) proton number 11; nucleon number 23
B1 each
(b) 12
23 − 11 = 12 B1
(c) 11
B1 11; B1 a neutral atom has equal numbers of protons and electrons
Q22Atom & nucleus · Core · Paper 1 style · 1 mark
(a)Two nuclides are isotopes of the same element. What must they have the same number of?[1]
Show answer
(a) C protons
Isotopes have the same proton number but different numbers of neutrons, so their nucleon numbers differ. B is the reverse of the definition.
Q23Atom & nucleus · Core · Paper 2 style · 5 marks
(a)Copy and complete the information for the three particles in an atom, giving the relative charge and relative mass of each: proton, neutron, electron.[3]
(b)State where in the atom each particle is found.[1]
(c)Explain why an atom has no overall charge.[1]
Show answer
(a) proton: +1, mass 1; neutron: 0, mass 1; electron: −1, mass about 1/1840 (negligible)
B1 each particle with both values correct
(b) Protons and neutrons in the nucleus; electrons orbit outside the nucleus
B1
(c) It has equal numbers of protons and electrons, whose charges are equal and opposite
B1
Q24Atom & nucleus · Core · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) A a positive ion
With one more proton than electrons the particle has an overall positive charge. C is wrong: the element depends only on the proton number, which is unchanged.
Q25Atom & nucleus · Standard · Paper 2 style · 7 marks
(a)In an experiment, a beam of alpha particles is directed at a very thin sheet of gold foil in a vacuum. Describe what is observed about the paths of the alpha particles.[3]
(b)Explain what each observation shows about the structure of the atom.[3]
(c)Suggest why the experiment is carried out in a vacuum.[1]
Show answer
(a) Most pass straight through undeflected; a few are deflected through small angles; a very small number are deflected through large angles (some bounce back)
B1 most go straight through; B1 some deflected; B1 very few deflected through more than 90°
(b) Most of the atom is empty space; the nucleus is positively charged (repels the positive alpha particles); the nucleus is very small and contains most of the mass (large deflections are rare)
B1 mostly empty space; B1 nucleus positive; B1 nucleus tiny and dense / contains most of the mass
(c) Alpha particles have a very short range in air; air molecules would absorb / deflect them
B1
Q26Atom & nucleus · Standard · Paper 1 style · 1 mark
(a)How many neutrons are in a nucleus of ²³⁵₉₂U?[1]
Show answer
(a) B 143
Neutrons = nucleon number − proton number = 235 − 92 = 143. D adds the two numbers instead of subtracting.
Q27Atom & nucleus · Standard · Paper 2 style · 5 marks
(a)In a fusion reactor two isotopes of hydrogen join:²₁H + ³₁H → ⁴₂He + XUse the conservation of nucleon number and proton number to identify particle X.[2]
(b)Explain why fusion only happens at extremely high temperatures, such as in the core of the Sun.[2]
(c)State one difference between nuclear fission and nuclear fusion.[1]
(b) Nuclei are positively charged and repel each other; they need very high kinetic energy (speed) to get close enough to fuse
B1 electrostatic repulsion between positive nuclei; B1 high temperature gives high enough kinetic energy
(c) Fission splits a large nucleus into smaller ones; fusion joins small nuclei to form a larger one
B1
Q28Atom & nucleus · Standard · Paper 2 style · 5 marks
(a)Carbon-14 is ¹⁴₆C and nitrogen-14 is ¹⁴₇N. Calculate the number of neutrons in each nucleus.[2]
(b)A student says these are isotopes because they have the same nucleon number. Explain why the student is wrong.[2]
(c)State which of the two nuclei has the greater positive charge. Explain your answer.[1]
Show answer
(a) carbon-14: 8; nitrogen-14: 7
B1 each
(b) Isotopes must have the same proton number (same element); these have different proton numbers (6 and 7), so they are different elements
B1 isotopes need same proton number; B1 these have 6 and 7 protons
(c) Nitrogen-14, because it has 7 protons and carbon-14 has only 6
B1 nitrogen-14 with reason: more protons (7 v 6); neutrons carry no charge
Q29Atom & nucleus · Challenge · Paper 2 style · 7 marks
(a)In a nuclear reactor a nucleus of uranium-235 absorbs a neutron and splits:²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + x ¹₀nCalculate x, the number of neutrons released.[2]
(b)State the name of this process.[1]
(c)Explain how this reaction can lead to a chain reaction, and how the chain reaction is controlled in a reactor.[3]
(d)State the form in which most of the energy released first appears.[1]
(c) The neutrons released can be absorbed by other U-235 nuclei, causing more fissions, each releasing more neutrons; control rods (e.g. boron) absorb some neutrons so that on average only one neutron from each fission causes a further fission
B1 released neutrons cause further fissions; B1 control rods absorb neutrons; B1 so the rate stays steady
(d) Kinetic energy of the fission products (daughter nuclei and neutrons)
B1
Q30Atom & nucleus · Challenge · Paper 2 style · 6 marks
(a)Chlorine has two common isotopes, ³⁵₁₇Cl and ³⁷₁₇Cl. State the numbers of protons and neutrons in each.[2]
(b)Explain why both isotopes have the same chemical properties.[2]
(c)A chloride ion, Cl⁻, is formed from a chlorine-37 atom. State the number of electrons in the ion.[1]
(d)Suggest why the two isotopes have different masses even though they are the same element.[1]
