The radiation can be classified into two groups as follows:

These radiations are considered in the design of biological shields.

1. Electro-magnetic waves.

2. Nuclear particles.

1. Electro-Magnetic Waves:

These waves are of high frequency and have high energy. These waves are known as X and gamma rays. These are the only electro-magnetic waves which need shields for the protection of personnel. Though they are similar to high rays, but possess higher energy and greater penetrating power. X and gamma rays are identical, but their sources of production are different. Both these rays have high penetration power, but they can be adequately absorbed by an appropriate thickness of concrete shield.

2. Nuclear Particles:

Nuclear particles consist of nuclei of atoms or their fragments. These fragments are known as neutrons, protons, alpha and beta particles. Except neutrons all the other particles possess an electric charge. On the other hand neutrons are un-charged and remain un-affected by electric field, until they interact by collision with a nucleus. They have no definite range and some of them may penetrate any shield.

Alpha, beta and proton particles carry electrical charge, which interact with electric field, surrounding the atom of the shielding material and lose their energy considerably. Generally these particles do not create a separate shielding problem, though accelerated protons at high energy levels may require heavy shielding comparable to that required for neutrons.

Thus X and gamma rays, and neutrons need protection shield. As stated above X and gamma rays are similar except in energy and origin. The biological hazards of radiation arise from the fact that the radiation interact with human tissues. In the process of interaction some of the energy of the human tissues is lost.

The energy loss is sufficient to ionize the atoms of the cells, upsetting the delicate chemical balance and causing the death of cells. If enough cells are affected, the organism dies. Thus the radiation must be reduced or weekend sufficiently, so that the remainder or left out radiation may not cause permanent damage to the persons exposed to it.

Apart from biological hazards, a very high temperature is also generated by the nuclear reaction. Thus the shielding is necessary to protect the electronic and other sensitive equipment in the vicinity.