AQA AS Level Physics Paper 1, June 2024: Question 1

14 marks · Hard difficulty · Extended Answer

Analyze particle interactions involving an electron neutrino and a chlorine-37 nucleus, specific charge of argon-37, quark Feynman diagrams for electron capture, and the nature of nuclear forces maintaining stability.

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Question

Question text

01 An electron neutrino interacts with a chlorine-37 nucleus to produce an argon-37

nucleus and an electron.

The interaction is represented by the equation:

37 37

ve + Cl → Ar + e

17 18

01.1 Explain, with reference to appropriate conservation laws, why the electron is emitted

in this interaction.

[2 marks]

01.2 Calculate the specific charge of the argon-37 nucleus.

[2 marks]

specific charge3 = C kg−1

01.3 In a different interaction, the argon-37 nucleus interacts with an electron.

Figure 1 represents the interaction of a quark in a baryon of the nucleus.

Figure 1

Deduce the exchange particle and the effect on the baryon.

Give one reason to support each answer.

[4 marks]

exchange particle

reason

effect on baryon

reason

01.4 The argon-37 nucleus decays into a stable nucleus.

Describe the nature of the forces that act between nucleons and how these forces can

maintain nuclear stability.

*03* In your answer, describe:

• the forces of repulsion and attraction that act between nucleons

• exchange particles associated with these forces

• the role of these forces in keeping the nucleus stable.

[6 marks]

Mark scheme

Show the mark scheme

Question Answers Additional Comments/Guidance Mark AO

01.1 MP1 2 AO2

To conserve charge

OR Must have some detail in support of both

conservation explanation for 2 marks.

To conserve lepton number

For charge conservation condone description

MP2 of RHS only:

Idea of how charge is conserved: idea of (extra) proton on RHS having charge

e.g. of +1(e) and an electron of -1(e)

LHS = 0 + 17 (𝜈𝜈 + n → p +e)

𝑒𝑒

RHS = 18 + (−1)

AND

Idea of how lepton number is conserved:

Charge conservation or lepton number can be

e.g. seen in the equation.

LHS = 1 + 0 Treat as neutral mention of conservation of:

RHS = 0 + 1 • momentum

• baryon number

601.2 Max 1 from: 2 1 × AO1

charge 1 × AO2

• use of specific charge = by substitution Condone their charge and their mass in the

mass

use of (including POT error)

• determines charge of argon nucleus = 18 × 1.6 × 10-19 2.88 × 10-18 (C)

Charge =

Mass = 6.2 × 10-26 (kg)

• determines the mass of argon nucleus

-27 For the mass of the nucleus, allow for

= 37 × 1.67 × 10 example:

• 37 × 1.66(1) × 10-27

• 18 × 1.673 × 10-27 + 19 × 1.675 × 10-27

4.6 × 107 to 4.7 × 107 (C kg−1)

01.3 MP1: Exchange particle: Do not allow W+ meson or W. 4 AO3

W+ Condone idea of W− being emitted by electron.

MP2: Effect on baryon:

Proton changes to a neutron / charge decreases by (+)1(e) Can see proton to neutron in diagram.

Accept positive baryon changes to neutral

Max 2 from the following reasons: baryon.

• it is the weak interaction.

• this is electron capture.

• quark changes flavour / up quark changes to a down Allow weak force or weak nuclear force.

quark / uud changes to dud

• lepton changes flavour / electron changes to a neutrino Where quark change is quoted must be

• idea of charge conservation at a vertex correct. Can see up to down in diagram.

Treat other conservations as neutral.

01.4 The mark scheme gives some guidance as to what statements The following statements are likely to be present. 6 AO1

are expected to be seen in a 1- or 2-mark (L1), 3- or 4-mark (L2)

Forces of repulsion and attraction that act between

and 5- or 6-mark (L3) answer. Guidance provided in section 3.10

nucleons:

of the ‘Mark Scheme Instructions’ document should be used to

assist marking this question. • (Repulsion =) Electromagnetic (between protons)

• (Attraction=) Gravitational force (between

nucleons) or idea that gravitational is negligible

Mar

Criteria • (Both repulsive and attractive =) Strong interaction

All three areas (as outlined alongside) covered with at Exchange particles associated with these forces:

least two aspects covered in some detail. • The pion is the strong interaction’s exchange

6 marks can be awarded even if there is an error and/or particle.

parts of one aspect missing. • Virtual photons for electromagnetic

• Treat mention of graviton for gravity as neutral

A fair attempt to analyse all three areas. If there are

5 several errors or missing parts then 5 marks should be

Role of these forces in keeping nucleus stable:

awarded.

• Idea that strong interaction is greater in magnitude

Two areas successfully discussed, or one discussed than any of the other interactions/ idea SI

4 and two others covered partially. Whilst there will be dominates.

gaps, there should only be an occasional error. • Strong interaction has short-range attraction acting

on neighbouring nucleons (up to 3 to 4 fm).

One area discussed and one discussed partially, or all

• Strong interaction has very short-range repulsion at

3 three covered partially. There are likely to be several

errors and omissions in the discussion. distances less than approximately 0.5 fm.

• Strong interaction acts between nucleons.

Only one area discussed or makes a partial attempt at

two areas. Further guidance:

Condone gluons as an alternative to pions.

1 One of the three areas covered without significant error. Condone electrostatic force as an alternative to

0 No relevant analysis. electromagnetic.

Total 14

How to answer it

Particle Interactions and Nuclear Stability

What this question tests

This exam question tests your core understanding of particle physics, specifically conservation laws in weak interactions, specific charge calculations for nuclei, Feynman diagram interpretation involving quarks, and the nature of nuclear forces responsible for holding nuclei stable.

Question 01.1

Conservation Laws in Particle Interactions

Explain, with reference to appropriate conservation laws, why the electron is emitted in this interaction.

✅ Correct Answer

To conserve charge: LHS = 0 + 17 = +17; RHS = 18 + (-1) = +17.
To conserve lepton number: LHS = 1 + 0 = 1; RHS = 0 + 1 = 1.

💡 Key Knowledge

Particle interactions must balance fundamental quantum numbers on both sides of the equation.
Electron neutrino has lepton number +1 and charge 0.
An electron has lepton number +1 and charge -1.

🧠 Exam Technique

To get both marks, you must provide detail supporting both conservation laws (charge and lepton number).
Show clear numerical breakdowns (e.g., LHS vs RHS sums) to guarantee credit.

❌ Common Errors

Failing to explicitly show numbers for both sides, or discussing irrelevant conservation laws like momentum or baryon number without connecting them to the particle emission.

Mark Allocation: 2 marks total (AO2)

Question 01.2

Calculating Specific Charge

Calculate the specific charge of the argon-37 nucleus.

✅ Correct Answer

Specific charge = 4.6 × 10⁷ to 4.7 × 10⁷ C kg⁻¹

📐 Step-by-Step Calculation

Formula: Specific charge = Charge / Mass
Charge of Argon-37 nucleus: 18 protons × 1.60 × 10⁻¹⁹ C = 2.88 × 10⁻¹⁸ C
Mass of Argon-37 nucleus: 37 nucleons × 1.67 × 10⁻²⁷ kg = 6.179 × 10⁻²⁶ kg
Calculation: (2.88 × 10⁻¹⁸) / (6.179 × 10⁻²⁶) = 4.66 × 10⁷ C kg⁻¹

❌ Common Calculation Traps

Using nucleon number (37) as the charge multiplier instead of the proton number (18).
Using electron mass instead of nucleon mass (approx 1.67 × 10⁻²⁷ kg).

Mark Allocation: 2 marks total (1 × AO1, 1 × AO2)

Question 01.3

Feynman Diagrams & Quark Analysis

Deduce the exchange particle and the effect on the baryon. Give one reason to support each answer.

✅ Correct Answers

Exchange particle: W⁺ (Do not allow W meson or W without sign).
Reason for exchange particle: It is the weak interaction / electron capture / quark changes flavour / charge conservation at a vertex.
Effect on baryon: Proton changes to a neutron (charge decreases by +1e).
Reason for effect: Positive baryon changes to neutral baryon (up quark changes to down quark).

💡 Key Knowledge

In electron capture, a proton-rich nucleus absorbs an inner orbital electron, converting a proton into a neutron via the weak interaction.
Charge of quarks: up = +2/3 e, down = -1/3 e. Changing an up quark to a down quark alters total charge by -1e.

🧠 Exam Technique

Make sure you include the charge symbol on the exchange particle ( W⁺ ). Omitting the plus sign loses the mark.
Explicitly link the quark change (u → d) to the overall change in the baryon type.

Mark Allocation: 4 marks total (AO3)

Question 01.4

Nuclear Forces & Stability

Describe the nature of the forces that act between nucleons and how these forces can maintain nuclear stability.

💡 Key Knowledge & Content Checklist

Forces of repulsion/attraction: Electromagnetic repulsion acts between protons (long range); gravitational attraction is negligible; the strong nuclear force acts between all nucleons.
Nature of Strong Force: Attractive from approx 0.5 fm up to 3–4 fm; very short-range repulsive at distances less than ~0.5 fm to prevent nucleons crushing together.
Exchange Particles: Pions (or virtual pions) are the exchange particles for the strong nuclear force (virtual photons for electromagnetic).
Role in Stability: The strong nuclear force is greater in magnitude than electrostatic repulsion at nuclear distances, balancing forces to keep the nucleus stable.

🧠 Extended Response Strategy (Level of Response)

This is a 6-mark extended writing question marked using levels (L1: 1–2 marks, L2: 3–4 marks, L3: 5–6 marks).
Ensure you cover all three prompt bullet points thoroughly: forces present, exchange particles, and how they maintain stability.
Use clear scientific terminology (e.g., femtometres , attractive , repulsive , pions ).

Mark Allocation: 6 marks total (AO1 - Level of Response)

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA AS Level Physics examination, Paper 1, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.