Edexcel IGCSE Physics: Double Science 复习笔记:7.1.4 Core Practical: Investigating Radiation

Edexcel IGCSE Physics: Double Science 复习笔记:7.1.4 Core Practical: Investigating Radiation

Core Practical 13: Investigating Radiation


Aim of the Experiment

  •  The aim of this experiment is to investigate the penetration powers of different types of radiation using either radioactive sources or simulations



  • Independent variable = Absorber material
  • Dependent variable = Count rate
  • Control variables:
    • Radioactive source
    • Distance of GM tube to source
    • Location / background radiation





Equipment List


  • Resolution of measuring equipment:
    • Ruler = 1 mm
    • Geiger-Müller tube = 0.01 μS/hr







Investigating radiation apparatus


  1. Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
  2. Repeat this three times, and take an average
  3. Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
  4. Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
  5. One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
  6. Repeat the above experiment for other radioactive sources




Analysis of Results

  • If the count over that interval falls to background levels (allow for a little random variation), then the radiation has all been absorbed
  • Note that some sources will emit more than one type of radiation
  • If the radiation is stopped by paper, the source will be emitting alpha
  • If the radiation is stopped by a few mm of aluminium (about 5 or 6) then the source is emitting beta
  • If some radiation is still able to penetrate a few mm of lead (5 or 6) then the source is emitting gamma




Penetrating power of alpha, beta and gamma radiation




Evaluating the Experiment

Systematic Errors:

  • Make sure that the sources are stored well away from the counter during the experiment
  • Conduct all runs of the experiment in the same location to avoid changes in background radiation levels


Random Errors:

  • The accuracy of such an experiment is improved with using reliable sources with a long half-life and an activity well above the natural background level




Safety Considerations

  • When not using a source, keep it in a lead lined container
  • When in use, try and keep a good distance (a metre or so) between yourself and the source
  • When handling the source, do so using tweezers (or tongs) and point the source away from you



Exam Tip

When answering questions about the core practicals you could try to remember the acronym SCREAMS:

  • S: Which variable will you keep the same
  • C: which variable should you change
  • R: what will you do to make your experiment reliable
  • E: what special equipment and equations are required
  • A: how will you analyse your results
  • M: which variable will you measure
  • S: what safety precautions will you take?