Nuclear Physics
Definitions: Nuclear Physics
Exam question
State what is meant by the mass defect of a nucleus.
9702/42 · Oct/Nov 2025 · Q9(a)
Model answer
The difference between the sum of the masses of the constituent nucleons separated to infinity and the mass of the nucleus.
Exam question
State what is meant by the binding energy of a nucleus.
9702/42 · May/Jun 2024 · Q9(a)
Model answer
The energy required to separate all the nucleons of the nucleus to infinity.
Exam question
State what is meant by nuclear fusion.
9702/41 · Oct/Nov 2023 · Q9(a)
Model answer
Two small nuclei join together to form one larger nucleus.
Exam question
Explain what is meant by a nuclear fission reaction.
9702/42 · Oct/Nov 2020 · Q12(a)(ii)
Model answer
A large nucleus divides into smaller nuclei, with neutrons released.
Exam question
State what is meant by radioactive decay.
9702/42 · May/Jun 2022 · Q10(a)
Model answer
The spontaneous emission of ionising radiation from an unstable nucleus.
Exam question
Radioactive decay is both random and spontaneous. State what is meant by: (i) random.
9702/42 · Feb/Mar 2025 · Q9(a)(i)
Model answer
It is impossible to predict when a particular nucleus will decay.
Exam question
Radioactive decay is both random and spontaneous. State what is meant by: (ii) spontaneous.
9702/42 · Feb/Mar 2025 · Q9(a)(ii)
Model answer
Decay is not affected by external or environmental factors.
Exam question
Define activity of a radioactive sample.
9702/41 · May/Jun 2025 · Q9(a)
Model answer
The number of nuclear disintegrations per unit time in the sample.
Exam question
Define radioactive decay constant.
9702/41 · Oct/Nov 2021 · Q12(a)
Model answer
The probability of decay of a nucleus per unit time.
Exam question
Define half‑life.
9702/42 · Feb/Mar 2025 · Q9(b)
Model answer
The time taken for the activity of a radioactive sample to halve.