Aggregates are the largest constituent of the total
weight of normal concrete. Thus concrete which is more effective
for the attenuation of fast neutrons can be produced by increasing
the water content through the use of hydrous aggregates such as
serpentine and limonite. For shields which are required to provide
protection mainly against gamma radiations and which have limitations
in regard to thickness, it may be desirable to use heavy concretes
which have densities greater than ordinary concrete. For this
purpose special heavy aggregates such as hematite, ilmenite and
cast iron or steel scrap may be used (Chilton et al., 1984; Profio,
1979; Kaplan, 1989).