Not trying to be trite when I focus a response on how does ionizing
radiation, whether alpha particles, beta particles or ionizing UV from
sunlight or other effect their end deleterious effect on human tissues
and glass. Absorption of energy breaks chemical bonds and forms free
radicals and ion pairs. These engender altered or different chemical
bonds. In the case of human cells, this can mean breaking normal
genetic structure and, potentially, creating new genetic code of
unknown value. In lenses, 'yellowing' is typically oxidation of
elements comprising the glass analogous to what happens to the white of
old newspapers. Inorganic glass is remarkably resistant to ionizing
radiation. Degraded glass is unlikely to be 'cleared' by UV. Coating
materials, however, contain organic carbon bonds which are readily
degraded to produce 'yellowing'. For this component of 'yellowing' UV
might help. As with organic 'dirt' in a white sheet hanging on a
clothes line, most organic molecules are more subject to degradation by
UV. You wonder where the yellow went when you brush your
teeth.......... Today, for a lot more money than a tube of Pepsodent,
your enterprising dentist will 'treat' your MC (yellow) teeth with UV.
SUM: If the yellow is within the inorganic glass structure, use it as
a paperweight. Yellowing is most likely confined to the MC. If
ionizing radiation has primarily affected carbon containing binders,
etc., used for the coating, UV might work well. To try seems the
obvious, since something from nothing is better than yellowed
nothing..... Have no experience, but if it were my lens, would be
very tempted to remove the glass element and place in the sun rather
than risk REAL damage to the housing from overheating. Finally, if one
of the members has access to a dental UV unit, it would be interesting
to test a more controlled approach with less IR and heating. Again,
removal of the element is suggested. Likewise, a solvent based
approach to removal of the coating might be effective.
Finally, after many years in biomedical research with radioactive
pharmaceuticals, I both applaud the efforts to understand the issues
relevant to 'radioactive' lenses AND remain dismayed how the unknowing
are so easily entrapped by misappropriated statements and histrionics.
The public library is a good place to start. Virtually none of the
questions which have been raised recently on this forum can be clearly
answered unless the reader understands the basic chemistry and physics
which underly the issues. I do applaud the efforts of some wise
efforts. Bottomline: we live on a radioactive planet in a Universe
whence energy is transfered by radiation which can ionize when
absorbed. Were it not for this, neither we or Zuikos would exist.
Unwise use has created human misery, none more tragic than the Radium
Dial Painters. Educated use has provided a world of materials, science
and medicine never dreamed of by our forefathers.
Regards,
Bill Hunter
On Friday, August 8, 2003, at 03:49 PM, Thomas Heide Clausen wrote:
I read somewhere that strong UV radiation should make the yellowing
disappear. Of course, it was on a Pentax mailing list, and I cannot
find the posting claiming that. Any of you guys out there, skilled in
the issue of radioactive lenses, who can either debunk that or
confirm it as a possibility for such unfortunate lenses.
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