Abstract : Although high-density concrete found limited use as a shielding material against X-rays before the large-scale development of nuclear reactors and similar devices, the latter have been almost entirely responsible for the research and development that have been done on the production and use of high-density concrete as a shielding material. Any sound concrete, in sections of sufficient thickness, can be used to construct a satisfactory biological shield, and where space is not a consideration, conventional concrete still appears to be the most satisfactory shielding material from the standpoint of cost. However, in many applications, space is a definite consideration. It is for these applications that research on development and use of high-density concrete has been done. Since the ability of a radiation shield to attenuate alpha, beta, gamma, neutron, and proton particles is almost directly proportional to the density of the shield, attempts have been made to develop a concrete ofmaximum density using various heavy aggregates. Densities in the range of 330 lb per cu ft have been obtained with experimental mixtures using iron as both coarse and fine aggregates. However, in most instances the high cost of iron and steel prohibits their use as concrete aggregate. (Author)