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  1. You have been given 3 sealed sources, 60Co, 137Cs & 152Eu, plus a set of 9 lead absorbers and 9 aluminium absorbers of different thicknesses
  2. Using tweezers place one of the sources in the shelf of the lead castle Geiger counter and shut the door
  3. Using the attached scaler timer determine the count over 100 sec
  4. Place one of the lead absorbers above the source in the Geiger counter and recount
  5. Repeat using each different thickness of lead absorber
  6. Measure the background with the medium thickness lead absorber in place but without the source
  7. Remove the lead absorber and measure the background again with the castle empty
  8. Correct the results for the background and plot a graph showing log counts per minute against absorber thickness
  9. From the graph determine the value of x½
  10. Using the graph provided*, determine the approximate value for the photon energy
  11. Repeat the experiment using the other 2 sources
  12. Repeat the whole experiment using the set of 9 aluminium absorbers