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

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

   

Method

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