Re: Re[2]: Thorium Lenses

[mgoldman@ucdavis.edu (Dr. Marvin Goldman)]

>     Thorium is added to glass to increase its strength.  Also add to
>     certain metal alloys to increase heat resistance....mike coogen
>
>
>______________________________ Reply Separator
>_________________________________
>Subject: Re: Thorium Lenses
>Author:  radsafe@romulus.ehs.uiuc.edu at hq2ccgw
>Date:    8/31/95 2:35 PM
>
>
>        Reply to:   RE>>Thorium Lenses
>I had some dealing with thoriated prism lenses out of aircraft sextants over
>ten years ago.  It was in the melt of the glass rather than being in a coating.
> There was no significant hazard unless the glass broke and controlling broken
>glass is, of course, easy.
>
>I'm not sure who made them, I think it was either Baird Atomic or Nuclear
>Chicago made them.
>
>I could never find out why thorium was needed in the glass.
>
>The original message is still not getting out.  Maybe this war story will be
>useful and maybe it won't.
>
>--------------------------------------
>Date: 8/31/95 12:31 PM
>To: GORDON MILLER
>From: radsafe@romulus.ehs.uiuc.edu
>     Don't think the second time went either...mike coogen
>
>
>______________________________ Reply Separator
>_________________________________
>Subject: Thorium Lenses
>Author:  radsafe@romulus.ehs.uiuc.edu at hq2ccgw
>Date:    8/31/95 12:38 PM
>
>
>
>Don't think the first try at sending this went properly so this is the
>second:
>
>
>
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>From: michael_coogen@hq2ccgw.hq.dla.mil
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>Subject: Re: Thorium Lenses
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Reply:
When I worked on this problem some 20 years ago, I was told that the
Thorium and rare earth oxides were added to the glass to improve the index
of refraction of presicion optical lenses, such as in periscopes and night
vision glasses, not to increase strength.  We actually did a study to
determine the alpha flux to the cornea and an estimate of risk to the eye.
The work ultimately resulted in an industry and NRC standard for
radioactivity in optical glass.
M.Goldman
U.Cal.-Davis