Low Background Steel — So Hot Right Now
https://hackaday.com/2017/03/27/low-background-steel-so-hot-right-now/
The nuclear age changed steel, and for decades we had to pay the price for it. The first tests of the atomic bomb were a milestone in many ways, and have left a mark in history and in the surface of the Earth. The level of background radiation in the air increased, and this had an effect on the production of steel, so that steel produced since 1945 has had elevated levels of radioactivity. This can be a problem for sensitive instruments, so there was a demand for steel called low background steel, which was made before the trinity tests.
Thanks to both of you. Total blind spot to me and I had no idea about low background steel.