Half-life: past paper questions
Real questions on half-life
The newest 20 of 37 written questions. Open one to see it on the real paper.
- 0625/33 · May/June 2026 · Q9c[2]
The isotope radium-223 is radioactive and has a half-life of 11 days. Calculate the fraction of a sample of radium-223 that remains after 33 days. fraction remaining =
See it on the paper → - 0625/43 · May/June 2026 · Q10c[2]
The object contains 1.0 × 10 –10 g of carbon-14. The object contained 8.0 × 10 –10 g of carbon-14 when it was made. Carbon-14 has a half-life of 5700 years. Estimate the age of the ancient wooden object. age = years (c) Scientists discover an ancient wooden object.
See it on the paper → - 0625/42 · February/March 2026 · Q10a(i)[1]
Complete the sentence about a planetary nebula. Stars expand when they run out of hydrogen to fuel nuclear reactions. A forms a planetary nebula.
See it on the paper → - 0625/42 · February/March 2026 · Q10a(ii)[1]
State what is at the centre of a planetary nebula.
See it on the paper → - 0625/31 · October/November 2025 · Q10c[3]
The half-life of radium-223 is 11 days. A sample contains 32 mg of radium-223. Calculate the time taken for the mass of radium-223 in the sample to decay from 32 mg to 4 mg. number of days =
See it on the paper → - 0625/32 · October/November 2025 · Q9b(ii)[3]
Fig. 9.1 shows the decay curve for a sample of iodine-131. count rate counts / s 240 210 180 150 120 90 60 30 0 (ii) 0 4 8 12 16 20 24 28 32 36 40 time / days Determine the half-life of iodine-131. Show your working clearly. half-life = days Fig. 9.1
See it on the paper → - 0625/42 · October/November 2025 · Q9b(i)[1]
Define half‑life of a radioactive isotope.
See it on the paper → - 0625/31 · May/June 2025 · Q10b[3]
A sample of radioactive material contains 72 mg of plutonium-241. Calculate the mass of plutonium-241 remaining in the sample after 42 years. mass of plutonium-241 remaining = mg (b) Plutonium-241 has a half-life of 14 years.
See it on the paper → - 0625/32 · May/June 2025 · Q10b[3]
A sample containing 60 mg of radon-222 decays to 7.5 mg in 11.5 days. Calculate the half-life of radon-222. half-life = days
See it on the paper → - 0625/33 · May/June 2025 · Q10b[3]
A sample containing 60 mg of radon-222 decays to 7.5 mg in 11.5 days. Calculate the half-life of radon-222. half-life = days
See it on the paper → - 0625/42 · May/June 2025 · Q9c(ii)[1]
Explain why a source with a short half-life must be used.
See it on the paper → - 0625/43 · May/June 2025 · Q11a[1]
Define the half-life of a radioactive source.
See it on the paper → - 0625/42 · February/March 2025 · Q9b(ii)[2]
percentage of strontium-90 remaining 75 50 0 25 0 0 5 10 15 20 25 30 35 40 45 50 age of sample / years 55 60 Fig. 9.1 The strontium-90 source is replaced with a new source after 15 years. Using Fig. 9.1, suggest why a strontium-90 source that is more than 15 years old needs to be replaced with a new source. The half-li...
See it on the paper → - 0625/12 · October/November 2024 · Q37[1]
How long does it take for the rate of emission to fall to 25 particles per second?
See it on the paper → - 0625/42 · February/March 2024 · Q9b(ii)[3]
The initial mass of this isotope of strontium in the source is 25 µg. Calculate the mass of the strontium isotope that decays in 87 years. mass = µg
See it on the paper → - 0625/21 · October/November 2023 · Q36[1]
Which time interval gives the half-life of X?
See it on the paper → - 0625/22 · October/November 2023 · Q35[1]
Which row correctly describes an example of radioactive decay?
See it on the paper → - 0625/22 · October/November 2023 · Q36[2]
What is the background radiation count rate?
See it on the paper → - 0625/22 · October/November 2023 · Q37[1]
What happens in the process of nuclear fission?
See it on the paper → - 0625/33 · October/November 2023 · Q10b[2]
The half-life of iodine-131 is 8 days. A sample contains 80 mg of iodine-131. Calculate the time taken to decay until 10 mg of iodine-131 remain in the sample. time taken = days
See it on the paper →
What examiners said
Comprehensive responses • Some candidates correctly recalled that a red giant forms a planetary nebula when it runs out of hydrogen to fuel nuclear reactions and that a white dwarf is at the centre of a planetary nebula. Limited responses • A common misconception was to state that a red super giant forms a planetary nebula. • Common incorrect responses for what is at the centre of a planetary neb...
— Examiner report, February/March 2026, 0625/42 Q10(a) (Cambridge)
Comprehensive responses • Some candidates correctly recalled that a red giant forms a planetary nebula when it runs out of hydrogen to fuel nuclear reactions and that a white dwarf is at the centre of a planetary nebula. Limited responses • A common misconception was to state that a red super giant forms a planetary nebula. • Common incorrect responses for what is at the centre of a planetary neb...
— Examiner report, February/March 2026, 0625/42 Q10(a) (Cambridge)
Many candidates found this question challenging, with only the strongest correctly determining that after 42 years the amount of plutonium-241 remaining was 9.0 mg. In many cases, the number of half-lives was calculated by dividing 42 by 14 to give 3 half-lives, but very few candidates could use this piece of information successfully. 41 was frequently halved three times, 72 was divided by 3, and...
— Examiner report, May/June 2025, 0625/31 Q10(b) (Cambridge)
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