Radiation is used in x-ray devices, nuclear power plants, industrial systems particle acceleration, and radioisotope projects, among other applications. With these examples, the radiation is a byproduct of a technology that we use such as x-rays. X-ray technology has offered nothing short of a revolution in medical science, however, they still produce harmful radiation and as such should be treated with care and caution. With that said, radiation protection is certainly achievable and there are many materials and measures that can be taken to minimize the harmful effects of radiation. Radiation can also cause damage to electronics or photographic film and as such these products need to be properly shielded from radiation as well when applicable.
There are two types of radiation: indirectly ionizing radiation and directly ionizing radiation. The indirectly ionizing radiations include: neutrons, gamma radiations, and x-rays. The directly ionizing radiation is mainly charged particles. The type of radiation involved determines the choice of the shielding material.
The principle behind radiation shielding is attenuation which reducesthe effects of a ray by blocking penetration of particles from passing through a barrier material. Charged particles react by electrons in the barrier material resulting in attenuation. Indirectly ionizing material are attenuated through photoemission, scattering or production of pairs. Major types of radiation include;
Gamma and x-ray particles – electromagnetic radiation that exhibit high energy.
Neutrons – particles with neither a positive nor a negative charge.
Alpha and beta radiations – Alpha particles have a positive charge and are easier to block while beta have a negative charge and are difficult to block.
Factors to consider in the selection of a shielding material include: cost effectiveness, their strength, ability to resist damage, thermal properties, and their efficiency of attenuation.
Shielding of gamma and x-ray
High density is preferred over low-density materials when shielding of gamma and x-ray particles. A general rule of thumb is the higher the material density, the more effective it will be in use as a radiation shielding material. The high atomic number of lead makes it appropriate in shielding this type of radiation. The degree of shielding can also be improved by increasing the thickness of the barrier material, however, some radiation can nevertheless penetrate through the barrier.
Shielding of alpha and beta
Thickness is not of importance in blocking this radiation. Plastic or a piece of paper can be used in blocking this type of radiation. Lead, however, is not efficient in blocking beta particles because they are capable of producing secondary radiations when passing through a high atomic mass and high density material.
Shielding of neutrons
Neutrons possess no charge and are thus capable of passing through high-density material like lead which are ineffective in blocking them. Neutron radiations are effectively blocked by elements with a low atomic mass.Elements with a low atomic mass can form cross sections that are capable of interacting with the neutrons. The preferred shielding materials for neutrons are hydrogen and hydrogen based materials. Compounds that have a high percentage of hydrogens in their structure, for example, water, are the most preferred. This is because they are relatively cheap and are efficient in their shielding properties. However,when shielding neutrons with low-density materials gamma rays can be emitted, hence when blocking neutrons it’s important to incorporate both low and high atomic number elements. The low-density elements block neutron by elastic scattering while the high-density block gamma rays through inelastic scattering.