When the Danube water level dropped recently, some old WWII ships were revealed. Is there enough demand for low-background steel to pay for their removal?
The article mentions that half-lives are such that it's not much of a problem even for "everyday steel" any more:
> But the days of low-background steel are coming to an end. Cobalt-60, the most common radioactive isotope found in our air from the nuclear blasts, has a half-life of around 5.3 years. Since the Partial Nuclear Test Ban Treaty in 1963, the atmosphere has become less, well, radioactive, meaning that increasingly the steel we make today – and hope to make in the future – is fit for our satellites after all.
In the article they say the problem is with radioactive contaminants in the large volumes of air that are pumped through the molten steel to purify it when it's made. My impression is that steel that's just exposed to the environment isn't necessarily contaminated.
The issue with radiation in the steel is due to atoms in the air when the steel is being cast. They are mixed into the material when it's molten.
The steel being made before 1945 is what protects against radiation.
Storage at the bottom of a river just means that it hasn't been found and recycled or scrapped already. It would still be "low background" if it had been stored elsewhere, exposed to air or not. The exposed surface layer can always be cleaned off or ground away. But what permeates the material is there for a long time.
The article also closes by noting that regular steel will work now, given the half life of the isotopes that are in steel, so there is no longer a need to salvage old metal, as I understood it.
I've seen that xkcd before. Maybe I made the wrong association because so far most wrecks which have been used for that were in deeper waters. Which when one thinks about it probably is for the simple reason that there were more fights at sea, than in rivers.
The most famous collection of wrecks used for this, at Scapa Flow, are in 12 to 45 metres of water [0]. Not really deep, as the ocean goes.
Generally the ships are deep enough that it was uneconomic to salvage them before, but not so deep that it's prohibitive to get at them now.
The USS Indiana, also mentioned in the article as a source of low-background steel, was never sunk [1]. It seems it was dismantled and meant to be scrapped, but no one got around to recycling the steel.
