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The experiment is quite simple. It involves firing a narrow beam of gamma-rays at a material and measuring how much of the radiation gets through. We can vary the energy of the gamma-rays we use and the type of absorbing material as well as its thickness and density.
The experimental set-up is illustrated in the figure below. We refer to the intensity of the radiation which strikes the absorber as the incident intensity, I0, and the intensity of the radiation which gets through the absorber as the transmitted intensity, Ix. Notice also that the thickness of the absorber is denoted by x.
From what we covered in the previous chapter we can appreciate that some of the gamma-rays will be subjected to interactions such as the Photoelectric Effect and the Compton Effect as they pass through the absorber. The transmitted gamma-rays will in the main be those which pass through without any interactions at all.
We can therefore expect to find that the transmitted intensity will be less than the incident intensity, that is
But by how much you might ask. Before we consider this let us denote the difference between Ix and I0 as ?I, that is
