Thorium in lenses

["RICHARD W. EDWARDS" <SHEA132@KGV2.bems.boeing.com>]

 Regarding the discussion re the applicability of the exemption to thorium
 coated lenses, perhaps the following may help:

 "Optical glass made with thorium oxide (in amounts ranging from 5 to 28% by
 weight), instead of the traditional silica, has a higher refractive index for
 given dispersions than most optical glasses."From Thorium--Its Industrial
 Hygiene Aspects, Roy E. Albert. 1966.

 This was one of a series of mongraphs put out by the American Industrial
 Hygiene Association and the US AEC Division of Technical Information. The
 information was provided by W.S. Sutton of Eastman Kodak.

 This would imply the purpose of the exemption was aimed at these glasses
 rather than coated lenses. What a regulator today will do in enforcement is
 another question entirely. Also, some of you may not be aware that the USNRC
 periodically reviews existing exemptions. I believe this is being done now,
 perhaps by the folks at ORNL.

 I hope this helps.

 This represents my opinion only and does not reflect the opinion of my
 employer or anyone else of importance.

 Thanks,
 Richard W. Edwards, Analyst          The Boeing Company
 Phone: (206) 393-1999                P.O. Box 3707, M/S 6Y-38
 Fax:   (206) 393-3060                Seattle, WA  98124-2207