Quote Originally Posted by benjiboy View Post
The lenses weren't coated with Thorium,Thorium Dioxide was part of the glass recipe to make it low dispersion.
I thought the lenses were coated with some thorium compound to improve their optical qualities but it makes more sense the way you say it.
Thorium is IN the glass, not ON the glass... Got it!

Quote Originally Posted by Gerald C Koch View Post
Yes and no. The most abundant isotope 232Th decays mainly by alpha emission but also by spontaneous fission and very rarely emission of two beta particles. The daughter isotopes must also be considered. The principal isotope of thorium decays as follows;

232Th -> 228Ra -> 228Ac -> ...

Both of the first two daughters decay by beta emission. There may be a gamma emitter in the chain. If you are interested you may trace the decay chain which ultimately results in a stable lead isotope.
This is good to know.
The reason I understood things to be the way I said is because xenon lamps and carbon rods are often doped with thorium and/or other rare earth elements to improve their spectral emission characteristics.
The electrodes inside a high pressure xenon lamp are made from sintered tungsten that has a small percentage of thorium mixed in or coated on. I forget which.
Regardless, I was led to believe that as long as you don't eat them or carry them around in your pocket, moderate amounts of thorium-treated (thoriated?) materials are mostly harmless and that you stand more chance of contracting cancer from a sunburn than you do from (conscientiously handled) thorium.

Anyhow, it's good to know more about thorium and, now, I have something new to go read about.