AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2018: Question 4

✅ Correct answer

2 charged particles and 2 neutral particles

This means an alpha particle is made of 2 protons and 2 neutrons.

💡 Key knowledge

• Alpha radiation is a helium nucleus.
• It has a charge of +2.
• It is large and relatively heavy compared with beta and gamma.

🧠 Exam technique

For a multiple-choice question, look for the particle count, not just the word “charged”. The mark scheme awards the option with 2 charged + 2 neutral.

❌ Common errors

• Mixing up alpha with beta particles.
• Thinking alpha is just “2 protons” without neutrons.
• Choosing answers with 4 particles total but the wrong split.

✅ Correct answer

It is the type of radiation with a negative charge.

Beta radiation is made of fast-moving electrons, so it carries a negative charge.

💡 Key knowledge

• Beta particles are electrons from the nucleus.
• They are much smaller and lighter than alpha particles.
• They are not the fastest moving type overall, and they do not have the greatest mass.

🧠 Exam technique

Use basic radiation facts:

• alpha = heavy, short range
• beta = negative charge, medium range
• gamma = no mass, long range

❌ Common errors

• Choosing “fastest moving” — that is not the accepted answer here.
• Thinking beta has the greatest mass.
• Confusing beta with gamma because both are penetrating.

✅ Correct answer

It has a very long range in air.

💡 Key knowledge

• Gamma is an electromagnetic wave.
• It has no mass and no charge.
• It is the most penetrating of the three types.

🧠 Exam technique

The mark scheme wants the range idea, so learn the standard phrase: “very long range in air”.

❌ Common errors

• Calling gamma a low frequency wave — gamma is actually high frequency.
• Saying it changes the charge or mass of the nucleus.
• Choosing alpha/beta properties by mistake.

✅ Correct answer

Iodine-131: the risk/activity associated with iodine-131 has decreased by a large amount because it has a short half-life.

Caesium-137: the risk/activity associated with caesium-137 will not have decreased by much because it has a long half-life.

💡 Key knowledge

• Iodine-131 half-life = 8 days
• Caesium-137 half-life = 30 years
• Short half-life means the activity drops quickly.
• Long half-life means the activity drops slowly.

🧠 Exam technique

This is an explanation question, so you need both the change in risk and the reason.

• State that iodine-131 has decreased a lot.
• State that caesium-137 has decreased only a little.
• Link each one to its half-life.

Top responses used the contrast clearly, which earned all 4 marks.

❌ Common errors

• Only saying “their activity changed” without comparing them.
• Not mentioning half-life at all.
• Mixing up which isotope has the short half-life.
• Saying “both emit the same type of radiation” and stopping there — that does not answer the risk change.

✅ Correct answer

2136

📐 Calculation: step by step

1. Find how many half-lives make 1/32.
   1/32 = 1/2 × 1/2 × 1/2 × 1/2 × 1/2
   So this is 5 half-lives.
2. Work out the time taken.
   5 × 30 = 150 years
3. Add this to the starting year.
   1986 + 150 = 2136

🧠 Exam technique

• Always identify the number of half-lives first.
• Use the half-life value exactly: 30 years.
• Show your working to gain method marks even if the final answer is wrong.

The mark scheme allows any correct method, including repeated halving.

❌ Common errors

• Using iodine-131’s half-life instead of caesium-137’s.
• Saying 1/32 means 32 years or 32 half-lives.
• Forgetting to add the time to 1986.
• Losing marks by not showing the half-life pattern clearly.

💡 Core facts to memorise

• Alpha particle = 2 protons + 2 neutrons.
• Beta radiation = negatively charged electron.
• Gamma radiation = very long range in air, electromagnetic wave.
• Short half-life = activity falls quickly.
• Long half-life = activity falls slowly.

🧠 How to score full marks

• Use the exact scientific wording in the mark scheme.
• Compare isotopes directly when asked about risk.
• In calculations, show half-lives, then multiply, then convert to a year.