AQA AS Level Physics Paper 2, June 2024: Question 5

1 mark · Medium difficulty · Multiple Choice

Identify the possible sequence of radioactive decays starting with nuclide P and ending with its isotope, given options involving alpha and beta-minus decays.

Practise this question

Question

Multiple choice question 05 asking for a possible sequence of radioactive decays starting with nuclide P and ending with an isotope of P. Four options are provided: A, one alpha decay followed by four beta-minus decays; B, one alpha decay followed by two beta-minus decays; C, two alpha decays followed by two beta-minus decays; D, two alpha decays followed by one beta-minus decay. Each option has a selection box next to it.
Question text

05 A sequence of radioactive decays starts with nuclide P and ends with an isotope of P.

Which is a possible sequence for these decays?

[1 mark]

A one alpha decay followed by four β− decays

B one alpha decay followed by two β− decays

C two alpha decays followed by two β− decays

D two alpha decays followed by one β− decay

Mark scheme

Show the mark scheme The mark scheme table shows question 05 has the correct key B, which corresponds to 'one alpha decay followed by two beta-minus decays'.

Question Key Answer

05 B one alpha decay followed by two β− decays

How to answer it

Radioactive Decay Sequences

What this question tests

This question assesses your understanding of how alpha (α) and beta-minus (β⁻) radioactive decays affect the proton number (Z) and nucleon number (A) of a nucleus, and how these changes determine isotopes.

Question 05 [1 mark]

Determining the Decay Sequence

✅ Correct Answer

B — one alpha decay followed by two β⁻ decays

1 mark awarded for selecting option B.

💡 Key Knowledge

  • Isotopes have the same proton number (Z) but a different nucleon number (A). For the final nuclide to be an isotope of P, Z must return to its original value.
  • Alpha decay (α): Nucleon number decreases by 4, proton number decreases by 2.
  • Beta-minus decay (β⁻): Nucleon number remains unchanged, proton number increases by 1.

🧠 Exam Technique

Track the proton number (Z) step-by-step. Since an alpha decay decreases Z by 2, you must exactly counteract this decrease by increasing Z by 2 using beta-minus decays (each increasing Z by 1). Therefore, 1 alpha decay requires exactly 2 beta-minus decays to return to the original element's proton number.

❌ Common Errors

Students often confuse the changes in nucleon number with proton number, or forget that an isotope of an element is defined strictly by having an identical proton number.

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.