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S6 Physics: Nuclear Radiation – Practice Paper 2 (Intermediate, 10 Questions)
S6 Physics: Nuclear Radiation – Practice Paper 2 (Intermediate, 10 Questions)
Paper two raises the level: the definition of the becquerel, randomness of single decays against the statistics of large samples, the three sources of background radiation, decay equations for radium-226 and phosphorus-32, why beta penetrates further, and finding half-lives from count rates and activities. The last item deals with the inverse square law.
Quick answer One becquerel is one decay per second; single decays are random while large samples follow exponential decay; background comes from cosmic rays, rocks and soil, and the body and food; five half-lives leave about 3.1%; radium-226 gives radon-222 with 86 protons; phosphorus-32 gives sulfur-32 with 16 protons; beta penetrates further because it is light and singly charged; 480 to 60 is three half-lives; 1600 to 100 kBq takes 32 days; doubling the distance leaves one quarter of the intensity.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 28 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S6 Physics | Nuclear Radiation: Alpha, Beta, Gamma, Decay Equations and Half-life |
| Level | Intermediate |
02 Questions (10 items)
- FoundationWhat is the definition of the becquerel, and how many decays happen each second in a 60 Bq sample?
- FoundationWhy is the decay of a single nucleus unpredictable while the decay of a large number of nuclei follows a law?
- FoundationWhat are the three main sources of background radiation?
- FoundationWhat percentage of a sample remains after five half-lives?
- IntermediateRadium-226 with 88 protons emits one alpha particle. Which nucleus is formed? Give the mass number and proton number.
- IntermediatePhosphorus-32 with 15 protons decays by beta emission. Which nucleus is formed, and why is the mass number unchanged?
- IntermediateWhy do beta particles penetrate further than alpha particles?
- ChallengeThe net count rate of a sample falls from 480 cpm to 60 cpm. How many half-lives have passed?
- ChallengeA sample with a half-life of 8 days falls from 1600 kBq to 100 kBq. How many days does this take?
- Error redoA student says doubling the distance from a source halves the intensity. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | One becquerel is one decay per second, so 60 Bq means 60 decays each second | The becquerel describes the rate of decay, not the energy of the radiation. |
| 2 | When one nucleus decays is a random event, but the statistics of a large sample follow exponential decay with a fixed half-life under the same conditions | Random and predictable are not contradictory: one describes a single nucleus, the other a large sample. |
| 3 | Cosmic rays; natural radionuclides in rocks and soil such as radon gas; natural isotopes in the body and in food, with medical examinations adding further dose | Background radiation cannot be removed, only measured and subtracted. |
| 4 | One over two to the fifth is one thirty-second, about 3.1% | After five half-lives very little activity is left, but it never reaches zero. |
| 5 | Radon-222 with 86 protons: 226 minus 4 is 222 and 88 minus 2 is 86 | In a decay equation the mass numbers and the proton numbers must balance on both sides. |
| 6 | Sulfur-32 with 16 protons, plus an electron and an antineutrino; a neutron becomes a proton so the mass number is conserved | Beta decay changes the proton number only, never the total number of nucleons. |
| 7 | A beta particle is light, fast and carries only a single negative charge, so it interacts less often and can pass through a few millimetres of aluminium; an alpha particle has two positive charges and much more mass and loses energy quickly | Penetration and ionising power are inversely related, so learn both together. |
| 8 | 480 halves to 240, then 120, then 60, so three half-lives have passed | Count one half-life for each halving instead of dividing 480 by 60. |
| 9 | 1600 halves to 800, 400, 200 and 100, which is four half-lives; four times eight gives 32 days | Find the number of half-lives first, then multiply by the length of one half-life. |
| 10 | A point source falls off as the inverse square, so doubling the distance leaves one quarter of the intensity, not one half | The inverse square law applies to point sources, and shielding or a large area source needs separate treatment. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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