Low-Background Steel (2018) | Hacker News Reader

Low-Background Steel (2018)

chemistryworld.com

83 pointstosh27 comments

Many (many) years ago I worked for the Earth & Space Sciences department at the University of Washington (setting up some of the first GPU farms! If only I'd known) and the lab where Minze Stuiver calibrated the Carbon-14 (and O18 and St90) timelines was in the sub-sub-sub-basement -- a single room with a descending spiral staircase in a storage room next to where they kept the ice cores. The facility was a kiln built from lead bricks made from the keel of a boat sunk before the modern atomic era.

A photo of the apparatus with the lead to the right: https://www.flickr.com/photos/jedwards/2281494063/

and a close-up of the kiln: https://www.flickr.com/photos/jedwards/2282285754/

IIRC a year or two after I left, they filled the whole space with concrete to build the foundation for a new neighboring building. They found someone who wanted the lead and bucket-brigaded them out of there, which must have been quite a day (the bricks are about 25lb each, and the size of a normal brick)

Radiation sensitive science experiments also have a need for low background lead. Here the need is for much older lead, ideally thousands of years old.

[1] https://www.theatlantic.com/science/archive/2019/10/search-d...

One important point here is that half-life of 5.3 years still takes decades to fall to acceptable levels. In the nuclear waste debate, I often see half-life used as "full-life", with disregard for its exponential nature.

The quick rule I use is 10 half-lifes to be considered "gone". Makes the mental math very easy.

10 half lives is only 1000x less.

I wouldn't drink a pint of dog shit. But I also wouldn't eat a grain of rice of dog shit.

A grain of rice size is less than 1000'th of the pint.

It does compound though, 20 half-lives is 1 million times less, and 30 is a billion.

But I also wouldn't eat a grain of rice of dog shit.

Yes you would, because you do. We all do. The FDA acceptable amount of fecal matter for wheat is 9 pellets per kilogram. Ginger, fennel, and mace can have up to 3mg of poop per pound. 5mg per pound of sesame seeds, 10mg per pound for chocolate.

It's pretty much no longer necessary except for all but the most demanding applications.

> Since the cessation of atmospheric nuclear testing, background radiation has decreased to very near natural levels, making special low-background steel no longer necessary for most radiation-sensitive applications, as brand-new steel now has a low enough radioactive signature that it can generally be used in such applications.

[1] https://en.wikipedia.org/wiki/Low-background_steel

Archives of the pre-AI internet are digital pre-war steel.

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?

I'm doubtful that the Danube is deep enough to protect against elevated background radiation, like the deep sea does.

Furthermore there is this nice graphic

https://en.wikipedia.org/wiki/Danube#/media/File:Danubemap.p...

marking the flow of the Danube in red, and beginning with the two first maps in

https://de.wikipedia.org/wiki/Liste_der_Kernreaktoren_in_Deu...

I'm even more doubtful. Of course it would depend on how far upstream the wrecks are, but...

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.

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.

You don't need very deep water to protect against radiation. As always, relevant xkcd: https://what-if.xkcd.com/29/

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.

[0] https://www.northlinkferries.co.uk/orkney-blog/wrecks-of-sca...

[1] https://en.m.wikipedia.org/wiki/USS_Indiana_(BB-58)

The water level and resulting radiation attenuation has nothing at all to do with the steel being "low-background steel" (1)

it's just that's where you typically find untouched pre-1945 steel objects.

The contamination occurs during the manufacture of the steel.

> Low-background steel is any steel produced prior to the detonation of the first nuclear bombs in the 1940s and 1950s

https://en.wikipedia.org/wiki/Low-background_steel

I'm curious why you can't just go to like an old building or something and pull steel from that?

If the building was put up before 1945, I would assume that you can.

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 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.

Here in Oslo we've been enjoying the Tirpitz ever since the end of the war, as covers during roadworks[1].

[1]: https://blog.usni.org/posts/2009/11/16/history-in-these-plat...

I'm curious why this can't be purified...

What is the PPM of radioactive material to normal lead/steel? For instance could you take a massive chunk of normal irradiated steel and divide it into small chunks, measure each chunk and keep the best X%, rinse repeat?

The cobalt is diffused pretty uniformly in the volume: it's blown in and alloys well. Making steel without any source of contamination would be possible but very expensive.

These arent physically visible or even microscopically isolated chunks, these are radioactive atoms diffused through the bulk metal. And as there are ~10^24 atoms in 100 grams of iron... go figure

There are much more radiation from Thorium and Uranium, sometimes K40, than from Co60 in metals, such as stainless steel, nickel and titanium. Copper purified by electroforming is surprisingly clean. It is usually used inside the lead shielding to reduce background further.

When I was going to school in the late 70's we toured the archeology lab at Cal State Northridge. The guide pointed out a section of pre-45 steel ship's propeller shaft (about 1.5 - 2' in diameter, hole through the center) that was used for radiocarbon dating.

Reply on news.ycombinator.com