Key Concepts: Radioactivity is the spontaneous emission of particles from unstable nuclei. Alpha particles (He nuclei), beta particles (electrons), and gamma rays are three types of radiation. Half-life is the time for half a sample to decay.
Section A: Atomic Structure and Radiation
1. State the units for activity, length and time used in radioactivity: becquerel, centimetre, hour, minute and second. [5]
2. Complete the table of nuclear radiation. [6]
| Type |
Composition |
Charge |
Penetration |
Stopped By |
| Alpha |
|
|
Low |
|
| Beta |
|
|
Medium |
|
| Gamma |
|
|
|
Lead/concrete |
3. Define atomic number, mass number and isotope, and interpret ¹⁴₆C. [4]
4. Describe how the atomic and mass numbers change for alpha, beta and gamma emission. [4]
Section B: Nuclear Equations and Detection
5. Complete the nuclear decay equations: [3]
(a) ²³⁸U → __He + __?
(b) ¹⁴C → __e + __?
(c) ⁶⁰Co → ⁶⁰Ni + __?
6. Name two detectors of ionising radiation and one source of background radiation. [3]
7. Describe a practical to investigate the penetration power of alpha, beta and gamma radiation. [4]
8. State that the activity of a radioactive source decreases over time and is measured in becquerels. [2]
Section C: Half-life and Decay
10. A radioactive sample has 800 nuclei with a half-life of 4 years. [3]
(a) How many nuclei remain after 4 years?
(b) How many remain after 12 years?
(c) What fraction remains after 8 years?
11. Describe one medical use and one industrial use of radioactivity. [2]
12. Explain the difference between contamination and irradiation. [2]
Section D: Nuclear Energy
13. State that nuclear reactions can be a source of energy in fission, fusion and radioactive decay. [2]
14. State what happens to a nucleus during: [2]
(a) Fission
(b) Fusion
15. Describe the fission of U-235 and the products formed. [3]
16. Explain how a chain reaction is controlled in a nuclear reactor. [3]
17. Explain the role of shielding around a nuclear reactor. [2]
18. Describe nuclear fusion, explain why it requires high temperature and pressure, and state where it occurs naturally. [4]
19. State two hazards of ionising radiation and one way to reduce risk. [3]
Total marks: 50
Mark Scheme
1. Bq, cm, h, min, s [5]
2. Alpha: helium nucleus, +2, paper; Beta: electron, -1, aluminium; Gamma: EM wave, 0, thick lead (any correct) [6]
3. Atomic number = protons, mass number = protons + neutrons; isotope = same Z, different A; 14/6 C has 6 protons, 8 neutrons [4]
4. Alpha: mass -4, atomic -2; beta: mass same, atomic +1; gamma: no change [4]
5. Correct nuclear equations [3]
6. Geiger-Muller tube/film badge; background from rocks or cosmic rays [3]
7. Place sources with absorbers; measure count rate; compare penetration [4]
8. Activity decreases over time; measured in Bq [2]
9. Time for activity/number of nuclei to halve [2]
10. 4 years: 400; 12 years: 100; 8 years: 1/4 [3]
11. Medical: tracers/radiotherapy; industrial: thickness control/sterilising (any two) [2]
12. Contamination = radioactive material on/in body; irradiation = exposure to radiation without material [2]
13. Fission, fusion and radioactive decay can release energy [2]
14. Fission splits nucleus; fusion combines nuclei [2]
15. U-235 absorbs neutron, splits into two daughter nuclei and releases neutrons/energy [3]
16. Control rods absorb neutrons; moderator slows neutrons [3]
17. Shielding absorbs radiation to protect workers and environment [2]
18. Fusion joins small nuclei, releases energy; requires high temp/pressure; powers stars [4]
19. Mutations/cancer/cell damage; reduce by shielding, distance, time [3]