
2000 year old Roman lead used for physics - peterburkimsher
http://www.aspera-eu.org/index.php?option=com_content&task=view&id=418&Itemid=98
======
yodon
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.

~~~
ams6110
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?

~~~
ISL
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.

~~~
caf
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.

~~~
averagewall
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...](http://historum.com/general-history/21841-world-lead-production-
last-2750-years.html)

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carlob
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.

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wenbert
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.

~~~
rangibaby
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.

~~~
flukus
> 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.

~~~
rangibaby
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.

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amexrap
Submitted 5 years ago:
[https://www.reddit.com/r/todayilearned/comments/pg14g/til_th...](https://www.reddit.com/r/todayilearned/comments/pg14g/til_that_ancient_roman_lead_is_valuable_for/)

~~~
IshKebab
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...](http://hackaday.com/2017/03/27/low-background-steel-so-hot-right-
now/)

------
JetSetWilly
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?

~~~
flashman
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...](https://www.scientificamerican.com/article/ancient-roman-lead-physics-
archaeology-controversy/)

~~~
jacquesm
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.

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Safety1stClyde
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.

~~~
JorgeGT
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.

