Gamma Radiation Absorption

Aim: To investigate how the absorption of gamma rays by lead depends on absorber thickness.

1. Click Add Source to place the gamma source, then click Start Count with the thickness set to 0 mm to record a baseline count rate.
2. Click Clear Count, increase the lead thickness using the slider, and start a new count. Repeat for a range of thicknesses from 0 mm to 100 mm, recording the count and time for each in the results table.
3. Change the material from lead to aluminium, gold or concrete and repeat your readings at the same thicknesses. How does the count rate at a given thickness compare between materials?
4. Plot count rate against thickness for lead. Is the fall in count rate linear, or does it look like a different kind of decay curve?
5. From your lead graph, estimate the thickness of lead needed to halve the count rate. Does this "half-thickness" stay roughly constant as you move to greater thicknesses?
6. Using your results for all four materials, rank them from best to worst absorber of gamma radiation. What property of a material do you think determines how good an absorber it is?