A brief reply then I quit. Good science is ipso facto. The science in
this issue is fascinating and fun. Counterpoint with misappropriated
facts is not contributory to anyone.
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.
That is not the discoloration that the topic addresses - and rare
earth compounds *are* radioactive sources!
Gross misappropriation: Being "rare earth" does not in any manner
equate to radioactive. Most do NOT include a naturally occurring
radioactive nuclide. Our everyday world of electronics and chemistry
and optics and ........ benefit from the widespread use of "rare
earths". Rare earths can impart color to materials. Inorganic rare
earth chemistry because of the common configuration of outer shell
electrons is unique. Delayed reactions with time are to be expected.
The term "rare earth" refers directly to the Lanthanide series of
elements.
Rebuttal would be wasted and not that which I intend. Suggest you
review:
http://science.howstuffworks.com/
framed.htm?parent=nuclear.htm&url=http://www.chemicalelements.com/
Lanthanide AND Actinide Series. Futher, it is the latter which
contains Earth's natural long lived radionuclides.
SIDE NOTE RE RADIUM DIAL RISK: The radium dial painters died primarily
from osteosarcoma since radium the chemical is handled as a bone salt
by the body once absorbed. While at the above URL, click on the
"Alkaline Earth Metals" to gain perspective on similar chemical
characteristics of this family and the relationship to bone.
Just because the glass contains a trace quantity
of a long lived radionuclide does not automatically link ionizing
radiation to the color change.
Thorium-228 half life is under two years!
This is GROSSLY misinforming the list with a factoid devoid of context.
If all Thorium was Th-228, there would be NO natural thorium on the
planet!!! Suggest you inform the group of the characteristics of
Th-232 and the relationship of Th-228 to the actinide chain if a
contribution is to be made. Better, rather than consuming valuable
time and bandwidth which should be devoted to photography, provide
educational URLs.
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.
But these types of glass use much more than a trace of radioactive
material - as can be confirmed by checking them with a counter.
What counter? Under what conditions? Spectroscopy? Standard used for
calibration? Units of measurement?
Hyperbole and anecdotal science do not contribute. If you want to
QUANTITATE a radioactive source, first learn about the multiple
conditions which must be satisfied and equipment needed for the isotope
in question. 'Checking with a counter' and 'much more than a trace'
are meaningless statements which only amplify misunderstandings.
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 +/-.
Diamond, and indeed any pure form of carbon, is certainly a special
case and not typical of the era but the definition of organic is
"carbon containing",
Not by any of the years of graduate chemistry training I received was
"organic" defined as "carbon containing"!!! Perhaps I did not receive
a good education. Organic chemistry includes metals - - you would die
without metaloproteins - - and inorganic chemistry would not be
possible as we know it without the element carbon.
As for the coating issues you raise......... Believe what you
choose, just be honest with the list about designating a grain of sand
to be a mountain, thus in turn, a mountain range. I do hope that some
with degraded lenses are able to recover, but skeptical. Whether
yellowed because of chemical changes induced by a rare earth which is
also radioactive or yellowed by ionizing radiation from a radioactive
rare earth provides insight as to potential for recovery. In the end,
it is probably a paper weight or a 'special effects' lens for b & w
photos. I quit this thread and turn back to great lenses and good
photo technique.
Keep your wrist watch on, your old 50/1.2 warm in your pocket and stock
up on B & W film.
Regards,
Bill Hunter
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