At 12:40 AM +0000 8/7/03, olympus-digest wrote:
>Date: Wed, 6 Aug 2003 18:47:23 +0100
>From: Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>
>Subject: Re: [OM] Radioactive glass
>
>In article , Joe Gwinn <joegwinn@xxxxxxxxxxx> writes
> >
> >Whoa! It's not nearly that dangerous, as it's very difficult to get
> >the thorium out of the glass, even if the glass is reduced to powder.
> >
>Its not an issue of getting the radioactive elements out of the glass.
>It is what happens to the alpha emission once you have ingested any of
>the fine glass particles or dust. Alpha radiation, not the decaying
>element, is then absorbed by LIVE tissue and that is the danger and the
>case of carcinogenic mutation.
Given the relative density of skin and glass, how much of the alpha radiation
will in fact escape the glass, even if it's been crushed? In practice, the
danger comes from chemically disolved material, not powder, as the range of the
alpha radiation in glass and in water is very short.
> >Nor is there all that much thorium in the glass, or the lenses would be
> >too radioactive for public sale to be permitted.
>
>Its enough to cause a significant discoloration after only a small
>fraction of the material decays. Much more radioactive materials are
>openly sold to the public - cut open a smoke detector and poke that in
>front of a geiger counter, for example. Its only a microgram or so of
>americium, but its still poses a significant radiation hazard if you
>swallow it.
Do we know the actual amount of thorium in the glass, as a mass percentage?
Americium is *much* hotter than an equal mass of thorium.
> >And, they would glow in the dark.
>
>The acceptable safe levels for ingested alpha emitters are extremely low
>and expecting dust to glow in the dark before any danger level is
>reached is a complete misunderstanding of radiation hazards. The
>problem is compounded because you have no way of knowing how much of the
>dust you are likely to ingest or how long it will stay in your body.
I was making a joke. Sorry.
> >In short, these lenses are no more dangerous than any other
> >photographic lens.
>
>In their normal form they pose no danger whatsoever, and I believe I
>made that clear enough. If it was a danger in its normal form then it
>wouldn't be much use as a photographic lens, would it? All your film
>would be fogged!
>
>The danger is very real and significant when the lens is pulverised as
>indicated on Brian's web site in an area where the dust could easily be
>ingested.
I wonder what happened to the folk that ground the glass into lenses for a
living. Given that they did this all day every day, they would be the first to
go, not us duffers. I don't recall ever reading stories about them dying like
rabbits from this or anything else associated with lens manufacture.
I can think of lots of reasons not to breathe ground glass, and radiation isn't
near the top of the list. Silicosis is more immediate, and in mining one keeps
it all quite wet to supress the dust.
Joe Gwinn
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