<强>铅内衬材料被安装在建筑物，以防止乘客的暴露于辐射。  There are three main types of radiation (alpha, beta, and gamma/X-ray) that humans can be exposed to, either naturally or through the normal operation of radiation emitting equipment or processes.  Gamma and X-ray radiation are very similar.  They are a penetrating type of high energy, high frequency electromagnetic radiation produced by X-ray operations in the medical field, and during the decay of radio-active materials in industrial applications.  Lead is the material of choice to offer shielding from gamma and X-ray radiation, since it is a dense element with a relatively high atomic number, which is important for the absorption of electromagnetic radiation.  Lead is cheap, available, and malleable, with a history of proven effectiveness for electromagnetic radiation protection.