AQA GCSE Physics Physics Paper 1 (Foundation), June 2023: Question 3

✅ Correct Answer

The nucleus of a carbon-12 atom and the nucleus of a carbon-14 atom have the same number of protons . [1 mark]

The nucleus of a carbon-12 atom and the nucleus of a carbon-14 atom have a different number of neutrons . [1 mark]

💡 Key Knowledge

• All atoms of the same element must have the same number of protons (atomic number). Carbon always has 6 protons.
• Isotopes are atoms of the same element that have different numbers of neutrons, giving them different mass numbers (e.g. 12 - 6 = 6 neutrons vs. 14 - 6 = 8 neutrons).

❌ Common Errors

Writing electrons instead of protons. The question specifically says "The nucleus of a... atom". The nucleus contains only protons and neutrons; electrons orbit the nucleus in shells!

🧠 Exam Technique

Cross off the words in the word bank as you use them. Double-check that your answers fit the context of the nucleus rather than the whole atom.

✅ Correct Answer

Tick option 2:

"The time taken for half the nuclei in a sample to decay." [1 mark]

💡 Key Knowledge

• Half-life has two accepted definitions in GCSE Physics:
  1. The time taken for the number of nuclei in a radioactive sample to halve.
  2. The time taken for the count rate (or activity) from a radioactive sample to fall to half its initial value.

❌ Common Errors

• "Half the time taken for all of the nuclei to decay" — radioactive decay is exponential and random; a sample never truly drops to absolute zero at a fixed "total time".
• "The time taken for one nucleus to split in half" — that confuses radioactive decay with nuclear fission!

✅ Correct Answer

Tick: Carbon-18 [1 mark]

💡 Key Knowledge

• Shortest half-life = least stable.
• Carbon-18 has a half-life of only 0.09 s . Because its nuclei decay very rapidly, it is the most unstable isotope listed.
• Carbon-15 has the longest half-life ( 2.45 s ), making it the most stable in the table.

🧠 Exam Technique

Always connect the words: Unstable = Decays quickly = Short half-life. Many students lose this mark by accidentally picking the largest number instead of reading "least stable".

✅ Correct Matches & Marks

• Contamination ➔ Accidental transfer of plutonium [1 mark]
• Irradiation ➔ Exposure to a beam of gamma rays [1 mark]

💡 Key Knowledge

• Irradiation: Exposure to ionizing radiation from an external source. The irradiated object does not become radioactive.
• Contamination: The unwanted presence of radioactive atoms on or inside materials/skin. The object remains radioactive as long as the source stays on it.

❌ Common Errors

Confusing the two terms. Remember: If physical radioactive atoms/particles touch you, you are contaminated. If rays pass through you, you are irradiated.

✅ Correct Answer

Tick option 3:

"To remove radioactive dust from their shoes." [1 mark]

💡 Key Knowledge

Dust particles can be radioactive materials (contamination). A sticky mat physically lifts solid matter off footwear so that workers do not transport radioactive material out of controlled zones.

❌ Common Errors

Selecting "To remove alpha particles" or "gamma radiation". Alpha particles and gamma rays are emitted radiation (particles/photons), not physical dust that sticks to shoes!

📐 Step-by-Step Calculation

1. Identify values from Table 3:
   Dose for aeroplane pilot = 0.072 mSv/day
   Dose for nuclear worker = 0.00050 mSv/day
2. Set up the ratio equation:
   Number of days = Pilot daily dose ÷ Nuclear worker daily dose
   Number of days = 0.072 / 0.00050 [1 mark]
3. Calculate final answer:
   0.072 ÷ 0.00050 = 144
   Number of days = 144 [1 mark]

🧠 Exam Technique

• Check the units: Both values are in mSv , so no unit conversion is needed before dividing.
• Show your working clearly: Even if you make a simple calculator typing slip, showing 0.072 / 0.00050 secures the first method mark.

✅ Correct Matches & Marks

• Nuclear fission ➔ Uranium [1 mark]
• Nuclear fusion ➔ Hydrogen [1 mark]

💡 Key Knowledge

• Nuclear Fission: The splitting of a large, unstable nucleus (e.g. Uranium-235 or Plutonium-239) in nuclear power stations.
• Nuclear Fusion: The joining of two light nuclei (e.g. isotopes of Hydrogen) to form a heavier nucleus (Helium), powering the Sun and other stars.

❌ Common Errors

Confusing fission (splitting apart big nuclei like uranium) with fusion (fusing together small nuclei like hydrogen). Remember: Fusion = Fusing together.