CP15 Investigate the Absorption of Gamma Radiation by Lead Flashcards
How?
Set up a Geiger counter and radioactive source, with a clamp and sheet of lead between them
Record the background radiation count on the GM tube over a long period (5-10 minutes
Find an average thickness of one sheet using a micrometre and multiple readings
Add each sheet one by one, recording the count over a much shorter amount of time than for the background count
Repeat 3 times
Graph thickness against count rate
Safety?
Reduce exposure to the gamma source by keeping it in a lead-lined box when not in use
Handle the source with tongs
Wash hands after holding lead
Keep source and arm’s length away
Reducing uncertainty?
Repeat readings as decay is random
Record over a long period
Uncertainty can be estimated as half of the range of the repeat readings
Why use cobalt 60
The count rate is high enough for readings but low enough to be safe
The half-life of 5 years so doesn’t need to be replaced often