4-17. ABSORBER DENSITY
A characteristic of an absorber, which determines its ability to absorb radiation is
atomic density. The more closely packed the atoms, the greater is the probability for
photon/electron interaction to take place. Consider two pieces of absorbing material --
wood and lead. Both are of equal thickness, but the lead will cause greater attenuation
because of its higher density. Due to its density, lead is an excellent shielding material
and is widely used in and around radiology departments. The shielding abilities of some
common shielding materials as compared to lead are shown in figure 4-9.
4-9. Various shielding materials and their relative effectiveness.
4-18. ABSORBER THICKNESS
Another factor that influences attenuation is the thickness of the absorbing
material. If photon energy and absorber density remain constant, then further
attenuation can be accomplished by simply adding more absorber material. In other
words, if 6 inches of concrete is good, then 12 inches is better. Figure 4-10 shows three
blocks of concrete of different thickness with each being subjected to x-ray beams
having the same photon energy. Attenuation is greatest with the thickest block of