Quote:
Originally Posted by wodin
Don't you mean they emit a minimum amount of radiation relative to the SAME AMOUNT of radioactivity? A curie of cobalt 60 or strontium 90 will emit the same number of gamma rays whether it's diluted in fifty liters of lead glass or not. The difference is the flux density at the surface. And stability is only in terms of chemical stability. Radioactive material is by definition unstable and all the dilution in the world will not make it less so.
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The issue here is that the lead makes a fine "shield". (Attempting to retrieve my college physics classes... That probably really means that the lead absorbs the gamma rays. It's been a long time since my undergrad years, though, so YMMV. I'd be happy to have a real expert correct me.)
As for chemical vs. radioactive stability: Of course the radioactive material will emit gamma rays over time. What we're concerned with here is keeping the material locked up inside the glass, where the lead shielding keeps it and it's radiation away from the public. And, of course, with keeping nasty radioactive stuff out of the hands of those who might wish to misuse it. The big-billet leaded glass appears to do that quite well. The small billets the French use now are sufficient to meet these goals as long as the dry storage is maintained; they would not suffice for 20K-years out in the weather.
Quote:
Originally Posted by wodin
In terms of life spans of civilizations, 20K years is a long time! Long enough to see several civilizations come and go. Would you have us believe that, say, middle age Europe would expend the resources to maintain dry storage and provide security for Egyptian glass?
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That's one of the big attractions of the "big billet" approach -- no dry storage needed. The big billets are really, really stable things. Big enough that even freeze-thaw cycles and spalling shouldn't be an issue over that time frame. Same for leaching via water and water-based erosion, etc. The idea is to bury them somewhere decently stable (to get as much head-start against erosion, etc. as possible). But they're stable enough to just be left out in the weather if need be.
So, to answer the question you actually asked: No, I don't believe that middle age Europe would expend the resources for that dry storage and associated security. The current approach in use in France is a case of allowing politics to get in the way of a better solution.
Xenophon