https://en.wikipedia.org/wiki/Low-background_steel https://en.wikipedia.org/wiki/Low-background_steel Note also: “Since the end of atmospheric nuclear testing,

https://en.wikipedia.org/wiki/Low-background_steel https://en.wikipedia.org/wiki/Low-background_steel Note also: “Since the end of atmospheric nuclear testing, background radiation has decreased to very near natural levels,[3] making special low-background steel no longer necessary for most radiation-sensitive applications, as brand-new steel now has a low enough radioactive signature that it can generally be used in such applications.”