Photoelectric interactions with shielding

Filled polymers play a role in primary and secondary protection against y-radiation. The photons interact with matter by photoelectric absorption and Rayleigh scattering. For primary partitions which separate an unshielded source from its surroundings, lead bricks or concrete blocks are used. For the secondary partitions which protect personnel from radiation, a protective shield or vest can be made by incorporating metal particles or lead oxide in rubber or plastic. Such shields are used by physicians and dentists or their patients to limit exposure to x-rays. The radiation... 

Photoelectric interaction in materials surrounding the detector can result in characteristic X rays in the lower energy region of the gamma-ray spectrum. For example, the Ka (72 keV) and Kp (85 keV) X rays are almost always part of the background in a spectrum of a detector shielded with lead. Commercially available lead shields for gamma-ray-spectrometer detectors are lined with thin cadmium and copper layers to attenuate these lead X rays. 

The most troublesome photoelectric interactions will be those with the shielding, usually lead. As shown in... 

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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