AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), November 2020: Question 2
10 marks · Low Demand difficulty · Short Answer
Answer questions on radioactive decay and hazards of tritium, including reading a decay curve, determining half-life, calculating percentage remaining, and identifying safety and scientific validation procedures.
Practise this questionQuestion
Question text
02 Between 1951 and 1992 the USA tested nuclear weapons in a desert.
02.1 Complete the sentence.
Choose the answer from the box.
[1 mark]
contamination irradiation ionisation decay
Radioactive dust from the nuclear weapons testing settled on the desert. This is
called radioactive .
The desert now contains radioactive tritium.
Figure 3 shows how the activity of the tritium in a sample taken from the desert
changed with time.
Figure 3
02.2 The sample was collected from the desert in 1992.
Determine the activity of the tritium in the sample in 2007.
[2 marks]
Activity = Bq
02.3 How much time did it take for the activity of the tritium in the sample to
decrease from 80 Bq to 40 Bq?
[1 mark]
Time = years
02.4 What is the half-life of tritium?
[1 mark]
Half-life = years
02.5 The sample started with 45 billion atoms of tritium.
After 4 years the sample had 36 billion atoms of tritium.
Calculate the percentage of the tritium in the sample that remained after 4 years.
[2 marks]
Percentage of tritium remaining =8 %
02.6 A scientist determined the activity of a sample of tritium every minute for 3 minutes.
Table 1 shows the results.
*07* Table 1
Time in minutes Activity in Bq
0 149
1 151
2 148
3 152
Why do the activity readings in Table 1 vary?
[1 mark]
Tick ( ) one box.
Radioactive decay is a random process.
Temperature changes affect the radioactive decay.
The number of radioactive nuclei keeps increasing and decreasing.
02.7 What safety precaution should scientists take when working with radioactive materials
in a laboratory?
[1 mark]
Tick ( ) one box.
Tie long hair back before handling the materials.
Use long tongs to handle the materials.
Wear safety goggles when handling the materials.9
02.8 Studies show that children born near the area of the desert containing tritium were
more likely to develop cancer.
It is important that the results from these studies are checked by other scientists.
What is this process called?
[1 mark]
*08* Tick ( ) one box.
Experiment review
Peer review
Results review
Test review
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
02.1 contamination 1 AO1
6.4.2.4
02.2 2007-1992 = 15 allow an indication of the 1 AO2
student reading from 15 years 6.4.2.3
on the graph
35 (Bq) allow an answer between 34 1
and 36 (Bq)
02.3 12.5 (years) 1 AO2
6.4.2.3
02.4 12.5 (years) allow the same value as their 1 AO1
answer to 02.3 6.4.2.3
02.5 36 000 000 000 36 1 AO2
(× 100) allow (× 100)
45 000 000 000 45
6.4.2.3
80 (%) 1
02.6 radioactive decay is a random 1 AO1
process 6.4.2.3
02.7 use long tongs to handle the 1 AO1
materials 6.4.2.4
02.8 peer review 1 AO1
6.4.2.4
Total 10
How to answer it
Radioactive Decay, Half-life & Radiation Safety
This question assesses core concepts from AQA GCSE Physics / Combined Science: Trilogy (Specification 6.4.2 & 6.4.3):
- Distinguishing between radioactive contamination and irradiation.
- Extracting data from radioactive decay curves (axes intervals and coordinates).
- Understanding and identifying half-life from graph trends.
- Calculating percentages from raw decay numbers.
- Recalling the random nature of nuclear decay, lab safety protocols, and the scientific process of peer review.
Radioactive Material Deposition
Contamination vs Irradiation
✅ Correct Answer
contamination
💡 Key Knowledge
- Contamination: The unwanted presence of materials containing radioactive atoms on other materials or skin.
- Irradiation: The process of exposing an object to nuclear radiation (the object does not become radioactive).
❌ Common Errors
Writing irradiation. Remember: the radioactive dust itself landed on the desert sand—it physically moved and remained there, which is contamination.
Reading Activity After Elapsed Time
Determining activity from the decay curve in 2007
📐 Step-by-Step Calculation
- Calculate elapsed time:
Time = 2007 − 1992 = 15 years [1 mark] - Read the value from the graph:
Find 15 years on the x-axis, follow vertically up to the curve, then horizontally across to the y-axis.
Activity = 35 Bq [1 mark]
🧠 Exam Technique
- Check axis grid scale: On the x-axis, 10 small squares = 5 years, so 1 small square = 0.5 years. At 15 years (30 squares from 0), the line crosses at exactly 35 Bq.
- The mark scheme allows between 34 and 36 Bq. Always draw pencil guide lines directly on the graph to show the examiner your method.
Determining the Half-Life
Time for activity to halve from 80 Bq to 40 Bq
✅ Correct Answers
- 02.3: 12.5 (years) [1 mark]
- 02.4: 12.5 (years) [1 mark]
💡 Key Knowledge
Half-life: The time it takes for the number of radioactive nuclei in a sample to halve, or for the activity (count rate) to decrease to half of its initial value.
- Initial activity at year 0 = 80 Bq
- Half of 80 Bq = 40 Bq
- Reading the time at 40 Bq gives 12.5 years.
🧠 Exam Technique: Spot the Direct Link
Question 02.4 asks for the half-life immediately after Question 02.3 asks for the time taken to drop from 80 to 40. Since 40 is half of 80, the answers to both questions are identical!
Percentage Calculation
Atoms remaining after 4 years
📐 Step-by-Step Calculation
- Formulate the fraction:
Remaining / Initial = 36 billion / 45 billion - Calculate percentage:
(36 / 45) × 100 = 0.8 × 100 [1 mark] - Final Answer:
80 % [1 mark]
❌ Common Errors
- Do not get confused by "billion": Since both quantities are given in billions, the 10⁹ terms cancel out completely:
36 / 45 = 4 / 5 = 80% . - Calculating decayed instead of remaining: The question asks for the percentage that remained (80%), not the percentage that decayed (20%).
Recall & Working Scientifically
Nature of decay, safety protocols, and peer review
✅ Correct Selections
- 02.6: Radioactivity fluctuation:
☑ Radioactive decay is a random process. [1 mark] - 02.7: Radiation safety:
☑ Use long tongs to handle the materials. [1 mark] - 02.8: Checking scientific studies:
☑ Peer review [1 mark]
💡 Scientific Principles
- Random Decay: It is impossible to predict when a particular nucleus will decay. This causes small natural fluctuations in count rate readings (149, 151, 148, 152 Bq).
- ALARA (As Low As Reasonably Achievable): Increasing distance using long tongs reduces radiation intensity significantly (inverse square law).
- Peer Review: Other qualified scientists independently scrutinise experimental methods and data to detect errors and prevent bias before publication.
❌ Common Errors
- Thinking temperature affects radioactive decay (nuclear reactions are completely unaffected by external conditions like temperature or pressure).
- Selecting safety goggles or hair ties as radiation protection—they do not block ionising radiation. Tongs keep the source away from the body.
Topics
Physics · P4: Atomic Structure
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.