ABSTRACT
This chapter discusses the relevant properties of the most common materials used in radiation shielding. Earth, meaning the soil atop its crust, not the planet itself, has many admirable qualities as a shield material besides the obvious one, its low cost. Notably, the water it contains enhances the effectiveness of the neutron attenuation because the mass of a proton is essentially equal to that of a neutron. This facilitates the transfer of energy from the particle to the shielding medium. Concrete has obvious advantages in that it can either be poured in place permanently or cast into modular blocks in configurations having considerable structural strength. Typical steel reinforcement has essentially no effect on radiation shielding properties. Concrete blocks may be used to shield targets, beam stops in a manner that allows their ready access for maintenance. Polyethylene is a very effective neutron shield because of its hydrogen content and its density, because it can attenuate “fast” neutrons.
