Gamma Radiation:

Gamma radiation is the most hard to shield against and, thus, presents the biggest problem in the reactor plant. A penetrating power of the gamma is due, in part, to the reality in which it has no mass or charge. Thus, it does not interact as often as do the other categories of radiation per given material.

Gamma rays are attenuated through processes that are functions of atomic number and mass (which is they all included interactions near the nucleus or interactions along with the electrons around the nucleus). A Gamma shielding is thus more efficiently performed through materials along with high atomic mass number and high density. Single such material is lead. Lead is dense and has about 82 electrons for each nucleus. Therefore, a gamma would interact more times in passing by eight inches of lead then passing by the similar thickness of a lighter material, such as water. As the gamma interacts along with the shielding material, it loses energy and finally disappears. Lead and lead alloys have been used to a few extents in nuclear reactor shields and have an added advantage of ease of fabrication. Since of its low melting point, lead could be used only where the temperatures do not exceed its melting point.