Some elements such as uranium, commonly used as fuel in nuclear power plants, are always radioactive; there is no nonradioactive form of them that naturally occurs in nature.(一些如鈾一般的元素，通常在核電廠用作核燃料，都是有放射性的；這些元素由于自身的性質是沒有無放射性狀態的。)

How it works: A patient inhales haimless nonradioactive Xenon gas, which is tracked by a scanner as it enters the brain.(工作原理病人吸人無害的、無放射性的氙氣。氙氣進人大腦后由掃描儀進行跟蹤。)

Isn't the nonradioactive form of thallium used for rat poison?(鉈的非放射性形態不是用于制造老鼠藥嗎？)