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S6 Physics: Nuclear Radiation – Error Revisit Practice (10 Questions)
S6 Physics: Nuclear Radiation – Error Revisit Practice (10 Questions)
Ten items revisit the usual slips: the nature and penetration of alpha, beta and gamma radiation, the meaning of half-life, activity falling from 800 Bq to 50 Bq in 20 days, 4.8 g reduced to 0.6 g in 24 years, mass defect converted to energy, and the change in mass and proton number after alpha plus beta decay.
Quick answer 1. two protons and two neutrons; 2. gamma; 3. the time for half the nuclei to decay; 4. one eighth, 12.5 per cent; 5. 50 Bq; 6. 0.6 g; 7. about 2.79 MeV; 8. 12 hours; 9. mass number 222 and proton number 87; 10. no.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 20 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S6 Physics | Nuclear Radiation: half-life, activity and nuclear decay |
| Level | S6 |
02 Questions (10 items)
- FoundationWhat does an alpha particle consist of?
- FoundationWhich of alpha, beta and gamma radiation has the greatest penetrating power?
- FoundationWhat is meant by the half-life of a sample?
- FoundationAfter three half-lives, what fraction of the original nuclei remains undecayed?
- IntermediateA source has a half-life of 5 days and an activity of 800 Bq today. What is its activity after 20 days?
- IntermediateAn isotope has a half-life of 8 years and a sample starts with 4.8 g. How much remains undecayed after 24 years?
- IntermediateA nucleus decays with a mass defect of 0.0030 u, and 1 u is equivalent to 931 MeV. How much energy is released?
- ChallengeThe activity of a source falls from 6 400 Bq to 800 Bq in 36 hours. Find the half-life of the isotope.
- ChallengeRadium 226 has mass number 226 and proton number 88. It emits one alpha particle and then one beta particle. Give the mass number and proton number of the final nucleus.
- Error redoA student claims that heating a radioactive source shortens its half-life so the radiation fades faster. Is that correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Two protons and two neutrons, that is a helium nucleus. | An alpha particle has no electrons and a charge of +2, and it is far heavier than a beta particle. |
| 2 | Gamma radiation. | Gamma is an electromagnetic wave with no mass and passes through thick metal, while a sheet of paper stops alpha particles. |
| 3 | The time taken for half of the nuclei in the sample to decay. | Half-life counts undecayed nuclei rather than the total mass of the sample. |
| 4 | One eighth, that is 12.5 per cent. | Each half-life halves the remaining number, so three half-lives leave 0.5 cubed, which is 0.125. |
| 5 | 50 Bq. | Twenty days is four half-lives, so 800 divided by 2 to the power 4, that is 16, gives 50. |
| 6 | 0.6 g. | Twenty-four years is three half-lives, so 4.8 divided by 2 to the power 3, that is 8, leaves 0.6 g. |
| 7 | About 2.79 MeV. | Multiplying 0.0030 by 931 gives 2.793, which rounds to 2.79 MeV. |
| 8 | 12 hours. | Since 6 400 divided by 800 is 8, which is 2 cubed, three half-lives have passed and 36 divided by 3 is 12 hours. |
| 9 | Mass number 222 and proton number 87. | Alpha decay removes 4 from the mass number and 2 from the proton number, while beta decay adds one proton and leaves the mass number unchanged. |
| 10 | No. | Nuclear decay is a random process inside the nucleus, and temperature, pressure and chemical state cannot change the half-life. |
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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