Core Practical: Investigating Radiation (Edexcel IGCSE Physics: Double Science)

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

1. Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a period of one minute
2. Repeat this three times, and take an average. Subtract this value from all subsequent readings.
3. 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
4. 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
5. 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
6. 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