Core Practical: Investigating Radiation (Edexcel IGCSE Physics)
Revision Note
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
Variables:
Independent variable = Absorber material
Dependent variable = Count rate
Control variables:
Radioactive source
Distance of GM tube to source
Location / background radiation
Equipment List
Equipment | Purpose |
|---|---|
radioactive sources (α, β and γ) | to use as a source of radioactive emission |
ruler | to measure the distance between the source and detector |
mount for radioactive source | to secure the source in place |
Geiger-Muller tube and counter | to measure the count rate of a radioactive source |
tongs | to safely handle the sources at a distance |
selection of absorbing materials (paper, aluminium foil, lead) | to place between the source and detector to investigate effect on count rate |
lead-lined containers for radioactive sources | to store sources in when not in use |
Resolution of measuring equipment:
Ruler = 1 mm
Geiger-Müller tube = 0.01 μS/hr
Method
Apparatus for investigating the penetrating powers of different types of radiation
Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a period of one minute
Repeat this three times, and take an average. Subtract this value from all subsequent readings.
Place a radioactive source a fixed distance of 3 cm away from the tube and take another reading of count rate over a period of one minute
Take a set of absorbers, i.e. some paper, several different thicknesses of aluminium (increasing in 0.5 mm intervals) and different thicknesses of lead
One at a time, place these absorbers between the source and the tube and take another reading of count rate over a period of one minute
Repeat the above experiment for other radioactive sources
Analysis of results
If the count rate is similar to background levels (allowing for a little random variation), then the radiation has all been absorbed
Note: some sources will emit more than one type of radiation
If the count rate reduces when paper is present, the source is emitting alpha
If the count rate reduces when a few mm of aluminium is present, then the source is emitting beta
If some radiation is still able to penetrate a few mm of lead, 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
Examiner Tips and Tricks
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?
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