Originally posted by Digitalis the discolouration of the lenses is not perfectly uniform, the edges of the lens are nearly always darker than the center of the glass element.
The edges being somewhat thinner, I would expect them to appear lighter as a matter of course.
Originally posted by Digitalis Wouldn't gamma emission events be statistically dwarfed by the amount of alpha/beta decay events?
That is a good question, the measurements done by Flickr user s58y using the Geiger-Mueller counter both with and without plastic caps went as follows:
Close in at front of SMC Tak 50/1.4...
w/o cap - 858 CPM
w/ cap - 778 CPM
Close in at rear of SMC Takumar 50/1.4...
w/o rear cap - 26838 CPM
w/ rear cap - 12512 CPM
I have been unable to find a source listing the relative energy distribution (eV) of alpha vs. beta vs. gamma in thorium oxide. As a constituent in the glass being darkened, it would be difficult to assign blame.
Steve