"...began to fall in 1963, when the Partial Nuclear Test Ban Treaty was enacted, and by 2008 it had decreased to only 0.005 mSv/yr above natural levels. This has made special low-background steel no longer necessary for most radiation-sensitive uses, as new steel now has a low enough radioactive signature."
"...began to fall in 1963, when the Partial Nuclear Test Ban Treaty was enacted, and by 2008 it had decreased to only 0.005 mSv/yr above natural levels. This has made special low-background steel no longer necessary for most radiation-sensitive uses, as new steel now has a low enough radioactive signature."
https://en.wikipedia.org/wiki/Low-background_steel