Radiation is no stranger to the earth. There have always been a large amounts of radiation coming from various sources that the earth is exposed to constantly, but the earth’s atmosphere absorbs most of them. However, nowadays, the types of radiation that people have to be concerned with come mainly from man-made sources. Many companies working in such fields as the medical, nuclear, and aerospace industries utilize and depend upon equipment that emits radiation. It is widely known that frequent contact and exposure to radiation are hazardous to human health and detrimental to the equipment. Therefore, many radiation shielding applications have been installed to protect people and the working facilities from the harmful rays as well as to comply with work-safety regulatory requirements.
For a long time, lead has been the leading material used in radiation shielding structures and applications. Due to its high density and thickness, lead is very effective in shielding various types of radiation including gamma, X-ray and neutron radiation. It is also praised for its wide availability, ease of fabrication, and high stability. Moreover, it is also a cheap material that can be incorporated into numerous shielding structures with the weights ranging from just a few grams to many tons.
However, lead has come under severe criticism in recent years due to its disastrous impacts on people and the environment. Research shows that lead can negatively impact human’s nervous and reproductive system, weakening the muscles and damaging the brain. For children, lead poisoning can impede their mental and physical development. For the environment, lead pollution can devastate the ecosystem and has serious negative impacts on living plants and animals. Therefore, the need for lead replacement and lead substitute materials is highlighted when selecting radiation shielding materials.
With the increased awareness of the toxicity of lead and the heightened regulatory pressures towards the use of lead, new materials are being developed to serve as lead replacement materials that are 100% lead equivalent in radiation shielding efficacy, such as:
• High density polyethylene – based: Plastic by itself can only be used to shield against alpha radiation, and some easily-absorbed rays. However, when reinforced and combined with other materials to produce plastic composite, its ability to attenuate radiation particles improves tremendously. Borated polyethylene and thermoplastic compounds are examples of lead substitute materials that have many advantages over lead such as light weight, lower cost, higher flexibility and longer lifespan.
• Tungsten – based: Tungsten, which is a hard and rare metal and often exists in the form of chemical compound, serves as an efficient lead replacement material. Tungsten alloys have high density and hardness, in fact almost 60 percent higher than lead, which are desirable characteristics for radiation shielding applications. They can be used to mitigate X-ray and gamma rays. Other benefits of tungsten-based materials include their high temperature resistance.
• Hydrogen – based: Hydrogen is of particular interest to be utilized as a component of radiation shielding due to its environmental friendliness and high availability. In addition, hydrogen can stop more low-energy particles and break down more high-energy heavy ions than other materials. Therefore, hydrogenous materials should be a promising material to replace lead.
Besides these above-mentioned materials, there are additional materials including other types of metal such as aluminum, copper and iron alloys that can be used as effective lead substitute materials depending on the application. In the future, even more lead replacement solutions and materials are expected.