At 2:37 AM +0000 8/4/03, olympus-digest wrote:
>Date: Mon, 4 Aug 2003 00:29:08 +0100
>From: Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>
>Subject: Re: [OM] Radioactive glass
>
>In article , Thomas Haegin <haegint@xxxxxxxxx> writes
> >Hi Mark,
> >thanks for that info! This whole issue of radioactive
> >glass in camera lenses is something I have never heard
> >of before
> >
>Not only used on camera lenses, but some coatings use thorium compounds
>which are also radioactive. I don't believe this coating material was
>ever used by Olympus though, but it caused a radiation alert when a
>colleague dropped a power connector onto a thorium coated optical window
>of a sensor system at work a few years ago.
>
>The danger with the solution proposed earlier in the thread, Brian
>Ayling's repair tip, is that both glass and coating are strong alpha
>emitters. That is fine if the glass and coating remain intact because,
>as any 20th century schoolboy knows, alpha radiation will not penetrate
>your skin and is stopped by even a single sheet of paper. Since your
>outer layer of your skin is dead cells, there is no danger from it
>absorbing any amount of alpha radiation.
>
>However, if the glass or coating is fragmented and even a single
>fragment ingested (take a look at how much fine powder is produced on
>image 3 again) then the alpha emission can be absorbed by living cells
>resulting in carcinogenic mutations. In an ingestible form, alpha
>emitters are the single most dangerous radioactive substances.
>
>Worryingly, Brian has what appears to be a vegetable patch only a few
>feet from what is now radioactively contaminated ground - and I bet he
>even uses his grass cuttings as a mulch! I wonder how many symptoms of
>leukaemia he, or his family, is suffering from now.
>
>I accept that the site is intended as a joke but this is no laughing
>matter and could easily encourage others to follow suit with supposedly
>worthless irreparable optics. Please DO NOT be tempted to reproduce the
>irresponsible humour of Brian Aylings site with any lens, whether OM or
>trash!
>
>**** NEVER DAMAGE A RADIOACTIVE GLASS ELEMENT ****
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. Nor is there
all that much thorium in the glass, or the lenses would be too radioactive for
public sale to be permitted. And, they would glow in the dark.
In short, these lenses are no more dangerous than any other photographic lens.
The only problem is that they eventually turn yellow, reducing transmission and
color fidelity.
Joe Gwinn
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