On Sunday, August 10, 2003, at 07:42 AM, Kennedy McEwen wrote:
In article , whunter <whunterjr@xxxxxxxx> writes
What I implied, but did not stress: Glass, a 'non-crystalline' melt
of
boron, silicon oxides and other elements, lacks the radiation
sensitive
organic carbon bonds. Glass is so resistant to radiation damage that
zillions of $ have been invested in the development of processes for
encapsulation of extrEMEly radioactive waste for 'eternity'.
Depending
on the ingredients of a specific glass, glass can be susceptible to
'fogging' or color change induced by intense ionizing radiation.
Distilling all this to the pragmatics of a discolored Zuiko from rare
earth containing coatings: First, the ionizing radiation level is
extremely low. While difficult to separate radiation induced change
from chemical degradation of the organic coatings, the science says
the
damage is on the exterior of the lens, not within the inorganic glass
matrix.
All of that would be fine Bill, but if you take one of these lenses
apart and isolate the yellow element, it doesn't take much work to
demonstrate that the discoloration is in the *volume* of the glass,
and certainly not just on the surface. At least, on the ones I have
examined, that is the case - I don't preclude that there are examples
where only the coating has yellowed. Many single coatins had a yellow
sheen in the first place, but that isn't what we are talking about
here.
Pictures I have seen of these lenses suggest that the 'yellowing' is
remarkably homogeneous. Does your experience concur? Your direct
observation of the lens in question is evidence, not speculation. I
have never owned this lens. With uniform discoloration in a relatively
short time period, I would suspect a slowly developing chemical
discoloration from the rare earth or contaminants more than coloration
induced by radiation. Just because the glass contains a trace quantity
of a long lived radionuclide does not automatically link ionizing
radiation to the color change. With this information, I am more
intrigued about the history and chemistry of the specific glass which
was used at that time. My general statement re the stability of glass
to ionizing radiation is fact. I have no scientific experience with
glass containing radionuclides but have seen many pieces of antique
Heisey glassware ('Marigold' as I recall) which utilized uranium as a
coloring agent. The radiation damage from the trace U-235 requires
decades to develop. It is manifested by physical degradation of the
glass which is not uniform. I suspect the uranium salts were either
not mixed well or were phase segregated in the molten glass.
Also, I am not aware of ANY organic compounds used for coatings - the
coating fabrication, being a plasma deposoition process, tends to
preclude most organics. I have specified diamond coating on some
optics, which technically is an organic material but not an organic
compound, and most coating materials are generally MgF or similar
materials.
Diamonds, inorganic (NOT organic) carbon, are remarkably resistant to
radiation, but not the technology of 1970 +/-. Vapor deposition of
fluorides, are certainly the standard of today. Likewise there are
organic based coatings available, but I lack detailed knowledge of
these products and their precise use in optics. My 'varnish' analogy
was dangerous because optical coatings are extremely thin films in
relation to a 'coat of varnish'. Do you know the exact technology
which was utilized to coat the lenses which have 'yellowed'? Published
tables identifying MC as purple, black, yellow, etc., contributes
nothing to the quest for understanding. Was it vapor deposition or
solvent based technology? Is there an Olympus scientist or scientific
technician associated with the manufacture of these specific yellowed
lenses who belongs to the list??
At any rate, I defer to one with direct experience. Uniform
discoloration strongly suggests a delayed chemical discoloration.
Inorganic chemical changes in the glass are most unlikely to be 'cured'
by UV, the original issue as I understand. Unfortunate.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|