The ethics of researh: destroying 2,000 years old artifacts

I don't know exactly why lead seems to be contaminated with PB-210, but a little digging suggested a lot of it comes from ore smelted out of metals operations in Brazil that becomes the source of a lot of US industrial lead applications. It could be that's just how the lead is found these days in the deposits we use.

PB-210 has a half-life of 22 years. Ancient lead, even if initially contaminated the same way, would be quite a bit less radioactive than it was when originally smelted. So that could by why ancient lead would be pretty useful.

As a history major I can use my expertise to say: burn and raze the lead. For the glory and honor of science!



But for real though, save a few but use most of them for research. It's what the Romans would want.

Well, how's this for irony:

https://www.osha.gov/dts/hib/hib_data/hib19970624.html

The Illinois Department of Nuclear Safety (IDNS) and the Center for Devices and Radiological Health of the Food and Drug Administration (FDA) have brought to our attention that some lead used in shielding is contaminated with radionuclides and that products containing this lead were widely distributed throughout the country.

IDNS coordinated with FDA regarding the nature of the contamination. FDA on June 13, 1997 issued a public health notice entitled "Radioactivity in Radiation Protection Devices" to health care professionals. All compliance and consultative personnel should be aware that certain lead aprons, gonad shields, thyroid shields and other lead devices used by health care employees could be contaminated. FDA health notice is attached for your use and it includes background information and recommendations.

Please distribute this bulletin to all Area Offices, State Plan States, Consultation Project Offices, and appropriate labor and industry groups.

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Still looking this up ...

TomB

tomBitonti said:

I'm kindof curious as to the problem of pollution of bars smelted today, and if there is no way to overcome the problem. I'm presuming that we have filled out environment with low level radioactive isotopes which create a signal that masks the dark matter signature.

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billd91 said:

I don't know exactly why lead seems to be contaminated with PB-210, but a little digging suggested a lot of it comes from ore smelted out of metals operations in Brazil that becomes the source of a lot of US industrial lead applications. It could be that's just how the lead is found these days in the deposits we use.

PB-210 has a half-life of 22 years. Ancient lead, even if initially contaminated the same way, would be quite a bit less radioactive than it was when originally smelted. So that could by why ancient lead would be pretty useful.

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Pb-210 is a product of a chain of decays starting with U-238, an isotope of uranium that's found pretty much everywhere on earth in varying quantities. So Pb-210 is found basically everywhere as well. I'm sure different lead mines will have slightly different amounts of Pb-210, but there's basically no way around getting Pb-210 when you mine lead. We can separate it out (I think using centrifuging because its atomic weight is different than that of stable lead isotopes), but dark matter detection experiments have to be incredibly sensitive because the signal they're looking for is tiny. So the labs are some of the most radiation-free places people can ever go, and it's pretty costly to purify the lead shielding to be as radiation-free as necessary. However, the ingots that have been dug up centuries ago and lost undersea have been protected from new Pb-210 deposits and so are a lot cleaner than anything mined and processed today.

tomBitonti said:

Well, how's this for irony:

https://www.osha.gov/dts/hib/hib_data/hib19970624.html

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This really has to do with strong medical standards. I suspect (just a guess without having more information than that link) that there wasn't any "extra" Pb-210 in the radiation shielding, but the legal/medical requirements are such that the shielding has to be cleaner than anything found in nature. That certainly happens.

freyar said:

Pb-210 is a product of a chain of decays starting with U-238, an isotope of uranium that's found pretty much everywhere on earth in varying quantities. So Pb-210 is found basically everywhere as well. I'm sure different lead mines will have slightly different amounts of Pb-210, but there's basically no way around getting Pb-210 when you mine lead. We can separate it out (I think using centrifuging because its atomic weight is different than that of stable lead isotopes), but dark matter detection experiments have to be incredibly sensitive because the signal they're looking for is tiny. So the labs are some of the most radiation-free places people can ever go, and it's pretty costly to purify the lead shielding to be as radiation-free as necessary. However, the ingots that have been dug up centuries ago and lost undersea have been protected from new Pb-210 deposits and so are a lot cleaner than anything mined and processed today.

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So if Pb-210 has a half-life of 22 years, and pretty much all lead that ever exists has been in existence for a really long time, how is it that Pb-210 is actually a problem?

Is something/some effect creating more Pb-210?

Janx said:

So if Pb-210 has a half-life of 22 years, and pretty much all lead that ever exists has been in existence for a really long time, how is it that Pb-210 is actually a problem?

Is something/some effect creating more Pb-210?

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Yes. U-238 is an unstable isotope of uranium with an extremely long half-life (about the age of the earth) and is found all over the earth. It is in fact the most common isotope of uranium. Since there is a lot of it, even though it has a long half-life, there are significant numbers of U-238 atoms that decay each day (or choose your favorite reasonable time unit). The product nucleus itself is unstable and decays much more quickly, and there is actually a whole chain of decays. One of the eventual products is radon gas, which can move around in the atmosphere a bit before decaying into a non-gaseous element that falls to the ground. One of the decay products of that is Pb-210. So anywhere you look, you will find some Pb-210, as far as I can tell, which includes lead that you dig up from a mine. Since it's chemically the same as the other lead isotopes you want to keep, it's not simple to separate out the Pb-210 from the "good" lead. We can do it reasonably well, but these physics experiments need extremely pure lead shielding --- even a little bit of radioactivity from Pb-210 can create enough noise to hide any possible signal of the experiment. The only way to purify lead well enough is to stick it away somewhere that new Pb-210 can't get for long enough that almost all the Pb-210 that's already there decays away. Unfortunately, that takes >100 years, which means you basically need to find lead that somebody lost somewhere isolated, like the bottom of the ocean, a long time ago.

freyar said:

Yes. ...snip...

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That makes sense. As my chemistry schooling is quite out of date, I vaguely recall that isotopes are basically variations of the element due to more or less neutrons (or whatever)

So I was thinking normal lead was getting neutron count messed with.

Rather than uranium decaying into something into something into Pb-210

I guess it's wierd that underground deposits of normal lead just happen to be near where U238 is decaying, but what do I know...

Thanks for the clarification

Janx said:

I guess it's wierd that underground deposits of normal lead just happen to be near where U238 is decaying, but what do I know...

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The point is that the U-238 is everywhere, in small amounts - a few parts per million in the rock and soil of the Earth. You need to have a richer deposit to make mining uranium worthwhile, but the stuff exists outside those deposits in amounts large enough to create a problem for people who need super-clean lead.

To be clear ...

Is the contaminant already in the lead, or mixed in from the environment (after the lead is mined)?

Once the contaminant is in the lead, is letting the lead sit in an isolated environment for an extended period of time the only effective way to remove the contaminant? (Letting what's there decay away, while not allowing any replenishment?)

If contaminant is already in the lead, is there any significant difference in the level of contaminant in lead from different natural sources?

If the contaminant is mixed in from the environment, is the environment different now than it was a couple of thousands of years ago (in terms of the amount of contaminant present)?

If the contaminant is mixed in from the environment, is there any way to process the lead to avoid contamination?

Thx!

TomB

I'd fall on the physicists' side of this, I think. The goal of archaeology can't just be to dig things up and store them indiscriminately. Items in common use (such as ballast) and abundance (such as ballast) can be studied and then a majority of them turned over, particularly when there's a clear and logical need for them. Also, the article also mentions 18th Cen. lead ingots, so clearly there's a range of possibility here - the scientists aren't just interested in 2,000 year old lead. 300 years old is OK too. So there's room.