Gamma attenuator:

Iron, while a medium weight element also functions well as a gamma attenuator. For gamma rays within energies of 2 MeV, roughly the similar mass of iron as of lead is needed to remove a specific fraction of the radiation. At higher and lower energies, therefore, the mass-attenuation effectiveness of lead is appreciably greater than in which of iron. In several cases, the selection of iron is based on temperature, structural, and economic considerations.

Water is a poor material for shielding gamma rays; therefore, huge amounts will serve to attenuate gamma radiation.
Concrete, as elaborates previously, is also a good attenuator of gamma rays and is superior to water. This is majorly a output of the presence of moderately high mass number components, such as calcium and silicon. As a common shield material, there is much to recommend about concrete; it is strong, inexpensive, and adaptable to both block and monolithic categories of construction.