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Re: Yellowing of radioactive lens elements....Re: [OM] 55/1.2

Subject: Re: Yellowing of radioactive lens elements....Re: [OM] 55/1.2
From: Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>
Date: Sun, 10 Aug 2003 12:42:33 +0100
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.

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.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers

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