2000 year old Roman lead used for physics | Hacker News Reader

2000 year old Roman lead used for physics

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I hope they are careful with the lead. When I was in grad school, there were still memories of a similarly large supply of low-radiation lead salvaged from a similar ship wreck that ended up being stolen for recycling as scrap (I remember hearing this lesson when I was at Princeton, which I believe is where the the theft happened)

Just because physicists consider the lead invaluable and irreplaceable doesn't mean recycling thieves will feel the same level of reverence towards it.

What causes "new" lead (whatever that means) to be more radioactive?

I mean, there's nothing really creating lead naturally in the environment, so isn't all lead pretty much the same age?

Atmospheric nuclear detonations have contaminated all un-so-shielded metals: https://en.m.wikipedia.org/wiki/Low-background_steel

I assume it is for the same reason as with steel[1] - the refinement process involves atmospheric air, and after we started detonating nuclear bombs, we raised the background radiation level of the atmosphere, and thus of the metals we produce.

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

There's a longer article explaining about Low-Background Steel on Hackaday:

http://hackaday.com/2017/03/27/low-background-steel-so-hot-r...

Part of naturally-abundant lead is Pb-210 (Wikipedia says 'trace', but from my low-background colleagues many talks, Pb-210 is a persistent problem). Pb-210 is part of the uranium-thorium decay chain, and it has the longest halflife (22 yr) after thorium.

If someone refines lead, it pulls out almost all of the impurities, except, of course, lead. As Pb-210 is chemically almost indistinguishable from the rest of the lead isotopes.

If, however, someone many years ago refined the lead, much of the Pb-210 will have decayed, lowering the backgrounds. This effect is important enough that even 50-100 year old lead of reasonable quality is worth expending considerable resources to salvage. One group in our lab spent a couple of people-years removing mercury from contaminated 50-100 year old lead .

The really precious stuff is ancient Roman lead, detailed in the article, that was submerged beneath the ocean for millenia. Not only has the 210 contamination decayed almost completely, but it has been shielded from cosmic-ray re-activation.

It makes me wonder if we shouldn't be smelting a large cache of high-purity lead today and stashing it away deep underground, for the science experiments a few hundred years hence.

Considering the relentless increase of lead production in the past few hundred years [1], with every passing year, old lead is probably becoming more and more readily available, to the point that in another 100 years it might be cheaper to just scrape it off rusted car wheels/etc. than deliberately store it for such a long time. As long as we don't get too greedy with recycling.

[1] http://historum.com/general-history/21841-world-lead-product...

Like, say, in the water pipes of a northern midwest city?

You seem to imply the Pb-210 only starts decaying after the refining occurs. I'm as curious about this as the grandparent - why?

Edit: Figured it out in the reddit thread linked elsewhere ( https://www.reddit.com/r/todayilearned/comments/pg14g/til_th... )

The key appears to be isolating the lead from co-occurring uranium which can decay into the Pb-210. It's not that the refined lead is losing Pb-210 any faster, it's just that there's no longer any uranium generating more of it. Fascinating!

I see how you can read it that way -- yes, your inferred 'key' is correct.

While I cannot guarantee such a theft will not happen, the gran sasso national laboratory is literally in an underground hole below the largest mountain in center/south Italy.

Unless a group of thieving dwarves and hobbits shows up it should be safe.

Or a contractor fixing the lights spots it on his way out. Not a lot of thefts happen by tunneling into buildings!

I don't see a contractor equipped to fix some lights make their way out with a few hundred pounds of lead, on top of that they would endanger their career and reputation for some 10's of $ whereas the job they were there for probably pays a large multiple of that.

Blaming the contractor is easy, but the vast majority of such thefts is done by insiders or security personnel.

This is exactly what was thought to have happened to the previous low background lead supply. It sat around in a big empty lab long enough for someone to notice it and notice that it was in a mostly empty lab.

I remember visiting the Gran Sasso Laboratories during a high school trip (my high school physics teacher had practiced particle physics for a bit before teaching). It was really one of the defining moments as a student, one of the things that led (no pun intended) me to study physics later.

Off-topic: I love reading articles that use 2-column format. I think it should be done more often. Although I wished the font would have been a "seriffed" one.

I think it's a bit weird to have to scroll down and up again. Doesn't make a ton of sense to me, especially if the article gets really long.

In this particular case it's also not responsive, which makes it a pretty bad experience on mobile. I would be curious if there's a good version of a 2-column layout; but I don't think this is it.

It's a good format for a printed article. Not so great on a screen.

Not sure about the down votes here. I think columns are acceptable in digital as long as they are responsive (e.g. 1 column mobile, 2 column normal, 3 column wide).

Why columns? Good-length columns minimize your eye movement and make it less tiring to read.

More than about 10 words per line require you to move your eyes too much horizontally or vertically and you can lose a train of thought etc.

That's fine if you can guarantee the user won't have to scroll up and down to read the content.

If you can't guarantee that, then the designer is just forcing a print convention where it doesn't belong. The solution is to make a narrower column.

> That's fine if you can guarantee the user won't have to scroll up and down to read the content.

Agreed. I consider Bootstrap's default breakpoints to be fairly trustworthy in the regard.

> Not sure about the down votes here. I think columns are acceptable in digital as long as they are responsive (e.g. 1 column mobile, 2 column normal, 3 column wide).

Which is not the case here. Resizing the browser keeps the same number of columns.

I meant in the general case of course. This specific site design, which appears to be from the early 2000s, is older than phones using the "real" internet so perhaps you can forgive them for not making a responsive website.

I hate 2-column format on screen, so I guess that's a matter of taste. Printed is ok though, maybe because you generally keep paper closer to your eyes than screen.

Submitted 5 years ago: https://www.reddit.com/r/todayilearned/comments/pg14g/til_th...

This has been submitted now because Hackaday posted an article today about low background steel, and it mentioned the use of ancient Roman lead:

http://hackaday.com/2017/03/27/low-background-steel-so-hot-r...

One thing I don't understand. Surely the lead atoms are much older than 2000 years - it is not like the Romans "created" the lead via nuclear fusion. The lead atoms must date back to the formation of the earth and beyond.

Therefore, the Romans merely concentrated these lead atoms into one place. But why hadn't all the unstable lead atoms decayed already long before? Why does it matter if the lead ingot is ancient or not, the actual lead matter is very ancient regardless?

Lead that has just been dug out of the earth was exposed to radiation from other minerals and cosmic radiation until very recently. On the other hand this batch of ancient lead was at the bottom of a lake for 2000 years, so it had time to lose some of its radioactivity while being shielded by water.

Pb-210 is a lead isotope that's a byproduct of uranium decay. When mined, all lead contains some Pb-210 as a result of U238 decay[0]. The lead can be refined to remove the U238, but not to remove Pb-210. So all 'fresh' lead contains some Pb-210 with a half-life of 22 years. If you use this for shielding in your experiment, you have to deal with its natural radioactivity.

(Now, what confuses me is how the Romans removed U238 from lead, because they must have done so in order to end up with lead that could decay over 2000 years. Maybe it happened as part of the smelting process.)

[0]https://www.scientificamerican.com/article/ancient-roman-lea...

Most old lead objects are cast, casting is a process where a liquid is poured into a mold where it is left to solidify. Presumably because both the melting crucible and the cast are under the influence of gravity while the metal is in the liquid phase the heavier elements will sort themselves to one end of the end-product, maybe even into the flues that will get cut off from the final product.

It would be much harder to keep the U238 evenly distributed throughout the lead during such a process.

Natural lead occurs along with small amounts of uranium and thorium. These radioactive atoms have radioactive lead isotopes in their decay products. So natural lead is constantly replenishing its levels of radioactive isotopes. When lead is mined, it is separated from the uranium and thorium, so no new radioactive isotopes are produced. You just have to wait for the radioactive lead present to decay. This can take 2000 years evidently.

To see the decay chain that includes ²¹⁰Pb see https://en.wikipedia.org/wiki/Decay_chain#Uranium_series

Because when atoms decay they tend to decay into other unstable elements that also decay.

I didn't see this in the article, but is it correct to think that if the isotope decays after 23 years, the reason that natural lead contains it is because natural lead itself is some kind of decay product.

Yep, the isotope is constantly replenished by decay of heavier atoms. When it is mined these heavier atoms are removed. You just have to wait for the radioactive isotopes to decay.

The isotope in question (Lead-210) is indeed a decay product of Uranium-238. However, not all lead is Pb-210, most of it is made of other, stable isotopes.

Since mining and refining lead removes the U-238 that would decay into more Pb-210, if you wait long enough (and shield it underwater), you get almost radiation-free lead, as the Pb-210 existing at the time of mining/refining eventually decays into non-radioactive Pb-206.

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