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7.1.4Radioactivity and Particles

Core Practical- Investigating Radiation — Edexcel International GCSE Science Double Award 4SD0 - Physics Revision Notes & Topical Questions

5 min read 5 parts Lesson 6 of 18

📚 Edexcel International GCSE Science Double Award 4SD0 - Physics Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Equipment and Set-up

The set-up must give a repeatable count rate so that the effect of each absorber can be compared fairly.

Geiger–Müller (GM) tube
  • Geiger–Müller (GM) tube A detector connected to a counter that records each ionising particle that enters the tube.
Radioactive source
  • Radioactive source A sealed source placed at a fixed distance from the GM tube to give a repeatable count rate.
Absorbers
  • Absorbers Thin sheets of paper, aluminium and lead placed between the source and the detector to test penetration.
Background count
  • Background count The count rate with no source present, mainly from natural radiation, which must be subtracted from every reading.

Part 2 of 5Method

Each reading uses the same time and distance so the results can be compared.

1
Measure the background count rate for a set time, such as one minute, with the source removed.
2
Place the source at a fixed distance from the GM tube and record the count over the same set time.
3
Subtract the background count from each measured count to obtain the corrected count from the source.
4
Insert one absorber at a time between the source and the tube, and record the count for each material.
5
Repeat each reading and calculate a mean, which reduces the effect of random variation in the count.

Part 3 of 5Analysis and Evaluation

Careful analysis separates the source's radiation from the background and shows which absorbers are effective.

Analysis and Evaluation
Corrected count
  • Corrected count The measured count minus the background count gives the count due to the source alone.
Expected pattern
  • Expected pattern Paper stops alpha, aluminium stops beta, and lead reduces gamma without stopping it completely.
Safety
  • Safety Keep the source in its container, handle it with tongs, and keep exposure time short and distance large.
Random variation
  • Random variation Count rates fluctuate because radioactive decay is random, so repeats and a mean make the result more reliable.

Part 4 of 5Worked Example

Question

  • A GM tube records 412 counts in 60 s with the source in place and 52 counts in 60 s with no source.
  • Calculate the corrected count rate in counts per second.

  1. Subtract the background count from the source count: 412 − 52 = 360 counts.
  2. The counts were recorded over 60 s, so the count rate is 360 ÷ 60.
  3. Count rate = 6.0 counts per second.

Answer 6.0 counts per second.

Part 5 of 5Exam Checklist & Tips

7.1.4 – Key Points for the Exam

  • GM tube A detector that produces an electrical pulse for each ionising particle that enters it.
  • Background radiation Radiation from natural sources and the surroundings that is present even with no source.
  • Count rate The number of radiation counts recorded per unit time, such as counts per second.
  • Corrected count rate The count rate from the source alone, found by subtracting the background count rate.
  • Absorber A material placed between a source and a detector to reduce the radiation reaching it.

Common Mistakes

  • Forgetting to subtract the background count from the readings taken with the source present.
  • Changing the distance between the source and the detector during the test, which alters the count.
  • Claiming that lead absorbs all gamma radiation; lead only reduces it.
  • Using a single reading rather than repeating and averaging each measurement.

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