5.2.6 Applications & Safety of Radioactivity
Comprehensive Assessment: 5 MCQs (Paper 2) • 5 Structured Questions (Paper 4) • 5 Practical Questions (Paper 6)
📋 Exam Instructions
- • Section A: 5 Multiple Choice questions (1 mark each)
- • Section B: 5 Structured theory questions (21 marks total)
- • Section C: 5 Practical questions (17 marks total)
- • Total: 43 marks • Time: ~45 minutes
Section A: Paper 2 (Multiple Choice)
Which type of radiation is used in household smoke alarms?
A factory uses radioactive sources to control the thickness of paper during production. Which radiation is most suitable?
Which material is most suitable for storing radioactive sources safely?
Medical equipment is sterilized using gamma radiation. Why is gamma preferred over alpha or beta?
A hospital uses a radioactive tracer to diagnose kidney function. Which property is MOST important for the radioactive isotope used?
Section B: Paper 4 (Structured Theory)
Americium-241 is used as the radioactive source in smoke alarms. It has a half-life of 432 years.
[Total: 5 marks]
(a) Explain why a smoke alarm source must have a long half-life. [2]
✓ MARK SCHEME:
- • So that the activity/count rate remains approximately constant
- • For the lifetime of the alarm / does not need frequent replacement
🎯 EXAMINER KEYWORDS:
"approximately constant" and "lifetime" are KILLER KEYWORDS. Do not just say "doesn't decay much" - examiners want the practical consequence!
(b) Explain why alpha particles are suitable for use in a smoke alarm. [3]
✓ MARK SCHEME:
- • Alpha particles are strongly/highly ionizing
- • They ionize air molecules, allowing current to flow
- • Smoke particles absorb/stop the alpha particles
- • Causing the current to drop, triggering the alarm
🎯 EXAMINER KEYWORDS:
You must mention BOTH ionization (creates current) AND absorption by smoke (breaks current). Just saying "ionizing" gets 1 mark out of 3!
Gamma rays are used to sterilize medical equipment and food.
[Total: 4 marks]
(a) State what is meant by sterilization. [1]
✓ MARK SCHEME:
- • Killing bacteria/microorganisms/pathogens
🎯 EXAMINER KEYWORDS:
One mark - just state the definition clearly. "Cleaning" or "making safe" is too vague!
(b) Explain how gamma rays sterilize the equipment. [2]
✓ MARK SCHEME:
- • Gamma rays have high energy/frequency
- • They damage/destroy the DNA of bacteria/cells causing cell death
🎯 EXAMINER KEYWORDS:
"High energy" alone is insufficient - you must link it to DNA damage or cell death. This is a HOW question, not WHAT!
(c) Give one advantage of using gamma rays rather than heating to sterilize equipment. [1]
✓ MARK SCHEME:
- • Does not damage heat-sensitive equipment / plastics
- • OR: Can sterilize equipment in sealed packaging
- • OR: More effective at killing all bacteria
🎯 EXAMINER KEYWORDS:
Any ONE valid advantage. Avoid "faster" (not always true) or "safer" (both have risks).
A student investigates the penetrating power of different types of radiation.
[Total: 3 marks]
(a) Explain why alpha radiation is dangerous when absorbed by living tissue INSIDE the body. [2]
✓ MARK SCHEME:
- • Alpha particles are highly/strongly ionizing
- • They cause significant damage to cells/DNA / cause mutations
🎯 EXAMINER KEYWORDS:
"Highly ionizing" is mandatory. Then link it to cellular damage. "Alpha is blocked by skin" is irrelevant to this INSIDE question!
(b) State why alpha radiation from a source OUTSIDE the body is relatively safe. [1]
✓ MARK SCHEME:
- • Alpha particles cannot penetrate (dead layer of) skin / are absorbed by air/paper
🎯 EXAMINER KEYWORDS:
One mark for stating low penetration with a specific example. "It's weak" is too vague!
The thickness of metal sheets in a factory is controlled using a beta source and a detector.
[Total: 5 marks]
(a) Explain why beta radiation is suitable for this application rather than alpha or gamma. [3]
✓ MARK SCHEME:
- • Beta has moderate/intermediate penetration
- • Alpha would be completely absorbed/stopped by the metal
- • Gamma would pass through with little/insufficient absorption
🎯 EXAMINER KEYWORDS:
This is a COMPARISON question - you must contrast ALL THREE types. Mentioning only beta gets 1/3 marks!
(b) If the metal becomes too thick, the count rate at the detector decreases. Describe how this information is used to control the thickness. [2]
✓ MARK SCHEME:
- • The (low) count rate triggers feedback to the rollers/machinery
- • The rollers increase pressure / compress the metal to reduce thickness
🎯 EXAMINER KEYWORDS:
You must describe the FEEDBACK MECHANISM. "The thickness changes" doesn't explain HOW the system responds!
Cobalt-60 is a radioactive isotope used in cancer treatment. It emits gamma rays and has a half-life of 5.3 years.
[Total: 4 marks]
(a) Explain why gamma rays are used to treat cancerous tumors. [2]
✓ MARK SCHEME:
- • Gamma rays can penetrate to reach the tumor deep inside the body
- • The high energy damages/destroys the DNA of cancer cells
🎯 EXAMINER KEYWORDS:
Two distinct points needed: PENETRATION (to reach tumor) and CELL DAMAGE (to kill cancer). Just "high energy" gets 1/2.
(b) Suggest why the half-life of 5.3 years is suitable for use in a hospital. [2]
✓ MARK SCHEME:
- • Long enough that the source remains active/useful for several years
- • Short enough that it does not remain dangerously active indefinitely / can be disposed of eventually
🎯 EXAMINER KEYWORDS:
This is a GOLDILOCKS question - not too long, not too short. You must explain BOTH extremes for full marks!
Section C: Paper 6 (Alternative to Practical)
A teacher is demonstrating the properties of radioactive sources to a class.
[Total: 3 marks]
(a) List THREE safety precautions the teacher should take when handling radioactive sources. [3]
✓ MARK SCHEME:
- • Use tongs / forceps / robotic arms (never handle directly)
- • Keep source in lead-lined box when not in use
- • Point source away from people / minimize exposure time
- • Wear radiation monitoring badge / use Geiger counter to check
- • Keep sources at maximum distance from body
- • Wash hands after handling
🔬 PRACTICAL TIP:
ANY THREE valid precautions. Be SPECIFIC - "be careful" or "use safety equipment" is too vague for marks!
A student measures the count rate from a radioactive source with different absorber materials.
[Total: 4 marks]
(a) Explain why the student should measure and subtract background radiation. [2]
✓ MARK SCHEME:
- • Background radiation is always present / comes from natural sources
- • To obtain the true/corrected count rate from the source alone
🔬 PRACTICAL TIP:
"Always present" establishes the problem. "True/corrected count rate" states the solution. Both needed!
(b) The table shows the student's results: Absorber | Count rate (counts/min) None | 850 Paper | 120 Aluminum (3mm) | 115 Lead (5mm) | 15 State what type of radiation the source is emitting. Explain your answer. [2]
✓ MARK SCHEME:
- • Alpha (and some gamma)
- • Large drop with paper indicates alpha present
- • Small remaining count indicates gamma present
🔬 PRACTICAL TIP:
You must JUSTIFY using data. "Alpha" alone gets 0 marks. "Paper stops most radiation" links observation to conclusion!
Workers in nuclear power plants wear radiation monitoring badges containing photographic film.
[Total: 3 marks]
(a) Explain how this badge monitors radiation exposure. [2]
✓ MARK SCHEME:
- • Radiation exposes/darkens the film (over time)
- • The degree of darkening indicates the total exposure / amount of radiation absorbed
🔬 PRACTICAL TIP:
Two-step mechanism: (1) film darkens, (2) darkness = measure of exposure. Just "detects radiation" is incomplete!
(b) Suggest why the badge is worn continuously rather than just during high-risk tasks. [1]
✓ MARK SCHEME:
- • To monitor cumulative/total exposure over time
- • OR: Low-level radiation can accumulate to dangerous levels
🔬 PRACTICAL TIP:
Key word is "cumulative" or "total" - emphasizes that exposure adds up over time, even at low levels.
A hospital stores radioactive sources in a locked room with thick concrete walls.
[Total: 3 marks]
(a) State THREE safety principles demonstrated by these precautions. [3]
✓ MARK SCHEME:
- • Shielding (concrete walls absorb radiation)
- • Distance (room separates sources from people)
- • Time (locked door limits exposure duration)
- • Security (prevents unauthorized access)
🔬 PRACTICAL TIP:
ANY THREE valid principles. Paper 6 loves the SHIELDING-DISTANCE-TIME trinity. Learn this by heart!
A student is investigating the inverse square law for gamma radiation using a sealed source and a Geiger counter.
[Total: 4 marks]
(a) State TWO precautions to ensure accurate distance measurements. [2]
✓ MARK SCHEME:
- • Measure from the center of the source to the detector window
- • Use a meter rule/tape measure with millimeter precision
- • Ensure the source and detector are aligned / at the same height
- • Use a set square to ensure perpendicular alignment
🔬 PRACTICAL TIP:
ANY TWO valid precautions. Paper 6 tests measurement technique as much as physics knowledge!
(b) The student obtains a count rate of 400 counts/min at 10 cm. Predict the count rate at 20 cm. [2]
✓ MARK SCHEME:
- • Inverse square law: I ∝ 1/d²
- • Distance doubled means intensity becomes 1/4
- • 400 ÷ 4 = 100 counts/min
🔬 PRACTICAL TIP:
Show the LOGIC: state the law, apply it (×2 distance = ×4 denominator = ÷4 intensity), then calculate. Formula without reasoning gets 1/2!
Quiz Complete!
Section A (MCQ): Auto-marked above
Section B & C (Theory/Practical): Self-assess using mark schemes
📚 Key Revision Points
Applications:
- • Smoke alarms: Alpha (ionizing, contained)
- • Thickness control: Beta (partial absorption)
- • Medical sterilization: Gamma (penetration)
- • Cancer treatment: Gamma (penetration + cell damage)
- • Medical tracers: Short half-life gamma emitters
Safety Principles:
- • Shielding: Lead boxes, concrete walls
- • Distance: Tongs, remote handling
- • Time: Minimize exposure duration
- • Monitoring: Film badges, counters
- • Storage: Locked, labeled, lead-lined
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