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S6 Physics: Nuclear Radiation – Practice Paper 1 (Foundation, 10 Questions)
S6 Physics: Nuclear Radiation – Practice Paper 1 (Foundation, 10 Questions)
Paper one builds the basic facts about the three radiations: what alpha, beta and gamma are, their penetration and shielding, subtracting the background count rate, the simplest activity and half-life sums, and how alpha and beta decay change the mass and proton numbers. The last item takes apart the claim that gamma rays carry negative charge.
Quick answer Alpha is a helium nucleus, beta a fast electron and gamma a high-frequency wave; alpha penetrates least and paper stops it; 320 minus 20 gives a net 300 cpm; 2400 Bq falls to 300 Bq in three half-lives; alpha decay cuts the mass number by 4 and the proton number by 2; in beta decay a neutron becomes a proton; gamma does not change the nucleus; 21.2 years is four half-lives leaving one sixteenth; 0.24 J over 3 kg gives 0.08 Gy; gamma carries no charge.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 25 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 | Foundation |
02 Questions (10 items)
- FoundationWhich three types of radiation can an unstable nucleus emit, and what is each one made of?
- FoundationWhich of the three has the weakest penetrating power, and what stops it?
- FoundationA Geiger counter reads 20 cpm with no source and 320 cpm with a sample present. What is the net count rate of the sample?
- FoundationA sample has an activity of 2400 Bq. What is its activity after three half-lives?
- IntermediateHow do the mass number and proton number of the daughter nucleus change after alpha decay? Use uranium-238 as the example.
- IntermediateWhat happens inside the nucleus during beta decay, and how does the atomic number change?
- IntermediateAfter gamma emission, do the mass number and proton number of the nucleus change, and why?
- ChallengeA radionuclide has a half-life of 5.3 years. What fraction remains after 21.2 years?
- ChallengeThree kilograms of tissue absorb 0.24 J of radiation energy. What is the absorbed dose?
- Error redoA student says gamma rays carry negative charge and are therefore deflected by an electric field. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Alpha rays (helium nuclei, two protons and two neutrons), beta rays (fast electrons) and gamma rays (high-frequency electromagnetic waves) | Alpha and beta are particles while gamma is an electromagnetic wave, which is why they need different shielding. |
| 2 | Alpha has the weakest penetration and a sheet of paper or a few centimetres of air stops it; beta needs a few millimetres of aluminium and gamma needs thick lead or concrete | Weaker penetration usually means stronger ionising power, so alpha dumps all its energy over a short distance. |
| 3 | 320 minus 20 gives 300 cpm | Background radiation has to be subtracted, or every reading comes out too high. |
| 4 | 2400 divided by 2 cubed is 2400 divided by 8, which gives 300 Bq | Each half-life halves the activity, so three half-lives means dividing by eight. |
| 5 | The mass number falls by four and the proton number by two: uranium-238 with 92 protons becomes thorium-234 with 90 protons, plus a helium-4 nucleus | An alpha particle is two protons plus two neutrons, so both numbers must drop. |
| 6 | A neutron turns into a proton and an electron plus an antineutrino are emitted; the proton number rises by one and the mass number stays the same | The electron comes from a change inside the nucleus, not from the outer shells. |
| 7 | They do not change; a gamma ray only carries away surplus energy from an excited nucleus, so the number of particles inside is unchanged | Gamma emission changes the energy state of the nucleus, not its composition. |
| 8 | 21.2 divided by 5.3 is four half-lives, so one sixteenth remains | Work out the number of half-lives first, then take one over two to that power. |
| 9 | 0.24 divided by 3 gives 0.08 Gy, that is 80 mGy | Absorbed dose is measured in gray, which is joules absorbed per kilogram of tissue. |
| 10 | Gamma rays carry no charge and are not deflected by electric or magnetic fields; alpha is positive and beta is negative, and they bend in opposite directions | Mixing up the charge of gamma and beta is the commonest conceptual error here. |
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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