Archived posting to the Leica Users Group, 2009/01/08

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Subject: [Leica] RE: hazards of the kodak aero ektar 175 /2.8 lens and other Thotium and Lanthinum
From: ejcaliguri at (Edward J Caliguri)
Date: Thu Jan 8 12:35:05 2009


Thorium is?the second in the ?Actinide element Series - that contains 
Uranium, (Lantinum starting it's own S eries ). Many lenses (Apo-Lanthars) 
contaied the oxide of these elements - ThO2 for eample in the Aero-Ektar, 
and gives glass Low Dispersion - ?High Refractive Index properties. It's use 
?was very good at the time. 

The oxides are fairly harmles , but Thorium metal is very radioactive and is 
looked at as a source of reactor fuel!! Th 232 , the most common goes throuh 
a number of alpha and beta decays over a thousand years or so before it 
turns to lead, Pb - Who says one element can't be turned into another 
naturaly?? :-) 

I wonder if after a thousand years someone will test these lenses, and see 
if the Ref. Index has changed because half the ThO2 will be PbO2? ----- 
We'll never know! 

Ed - I Just like chemistry!