Low-Background Steel

I've known about this for a long time, but only in the past couple years started to appreciate how much of the background radiation has gone away.

> World anthropogenic background radiation levels peaked at 0.11 mSv/yr above natural levels in 1963, the year that the Partial Nuclear Test Ban Treaty was enacted. Since then, anthropogenic background radiation has decreased to 0.005 mSv/yr above natural levels.

Im curious how much of the decay is half life related, and how much is that the particles have deposited themselves onto the planet, gotten out of the air.

Found thanks to this comment: https://news.ycombinator.com/item?id=34960377