GCSE Physics - Radioactivity

(a) Half-life calculation [2 marks]:

• Recognizes that mass decreases from 48g → 24g → 12g → 6g (1 mark)
• Therefore 3 half-lives have occurred in 6 hours
• Half-life = 6 ÷ 3 = 2 hours (1 mark)

(b) Mass after 9 hours [1 mark]:

• 9 hours = 4.5 half-lives
• Mass will be 3g (1 mark)

Accept clear working showing logical steps

• Alpha radiation has short range/is easily stopped by skin (1 mark)
• When ingested, alpha particles release all their energy inside the body/can directly damage internal organs (1 mark)

Accept any clear explanation of internal vs external damage

• Subtracts background count: 240 - 20 = 220 cpm (1 mark)
• Converts to counts per second: 220 ÷ 60 = 3.67 cps (1 mark)

Accept 3.7 cps or 3.66... cps

• Mass number stays the same (1 mark)
• Atomic number increases by 1 (1 mark)

Both points needed for full marks

• Alpha particles ionize air between plates/create current (1 mark)
• Smoke particles block/absorb alpha particles, reducing current/triggering alarm (1 mark)

Accept answers referring to interruption of current or reduced ionization

• Recognition of inverse square law (1 mark)
• Count rate will be 20 counts per second (1 mark)

Award full marks for correct answer with working

• Contamination is when radioactive material gets onto/into something (1 mark)
• Irradiation is when something is exposed to radiation (1 mark)
• One relevant example of each (1 mark)

Examples might include:
Contamination: radioactive dust on clothing, radioactive particles in food
Irradiation: medical X-rays, sterilizing equipment

• Mass number decreases by 4 (1 mark)
• Atomic number decreases by 1 (1 mark)

Must show understanding that alpha decreases mass by 4 and atomic number by 2, while beta increases atomic number by 1

Lead has higher density/atomic number (1 mark)

Accept references to lead being denser or having more protons

Different rocks contain different amounts of radioactive materials/different altitudes have different cosmic radiation exposure (1 mark)

Accept any reasonable explanation related to natural radiation sources