A bit of a tangent, but somewhat related to your bit about concrete: steel salvaged from ships built before 1945 is less radioactive than modern steel and is us

A bit of a tangent, but somewhat related to your bit about concrete: steel salvaged from ships built before 1945 is less radioactive than modern steel and is useful for devices that are extremely sensitive to radiation: https://en.wikipedia.org/wiki/Low-background_steel https://en.wikipedia.org/wiki/Low-background_steel The reason the modern stuff is more radioactive is the massive number of atmospheric nuclear weapons tests conducted starting in 1945. I imagine the concrete has the same issue.