Photoelectric effect gamma rays from

Gamma-rays of higher energy, rather than interacting with the field of the whole atom as in the photoelectric effect, interact with the field of one electron directly. This mode of interaction is called the Compton effect after its discoverer, A. H. Compton. In the Compton effect an electron is ejected from an atom while the y-ray is deflected with a lower energy. The energy of the scattered y-ray, Ey, is expressed by the equation... 

The probability of fhese interactions depends not only on the energy of the gariuna ray but also on the atomic number, Z, of the material. Figure 25.6 plots the relative probability of Compton interactions, a, with photoelectric effect, t, and pair production, k. Higher Z materials, such as lead are more likely to have photoelectric effects than Compton scattering. From the standpoint of shielding gamma rays, photoelectric effect is preferable as discussed later. 

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