Low-background metal.

“One odd consequence of humanity’s 77-year flirtation with atomic weapons is that the steel we produce is now ever-so-slightly radioactive. The radiation isn’t strong enough to pose a health risk, but it does interfere with some sensitive scientific and medical equipment. … This quirk of the nuclear age has created a lucrative but sometimes controversial industry for steel produced before 1945 and centuries-old lead—often sourced from shipwrecks. These “low-background” metals (referring to their low levels of background radiation) have played a key role in treating patients at hospitals, advancing the field of physics, and exploring the cosmos.” ~ learn more