I spent couple of years slowly reading in military databases, patents and books. I found and posted an article before about Kodak and Leitz lenses night performances. When the color temperature changes , these lenses turns to strong reddish yellow colors on skins. I could not understand the reason for years and I found that the main reason was the use of partial dispersion glasses. The color scale changes to one color dominance with partial dispersion glasses. I think these glasses are neutral at daylight.
I started to search in Leitz and Kodak patents and found that the use of % 20 strontium use in partial dispersion glasses. I need to indicate that half of the new Leica lenses are partial dispersion glasses.
Strontium is used mainly in cathode tubes with barium and they dont emit x ray.
That material is radioactive and strongest byproduct of nuclear explosions.
Second radioactive source is Thorium Fluoride use in Leica glass coatings until 1990s.
Third radiation source is thorium addition to glasses.
I want to say may be thorium is not used by Leica now but strontium dominate the patents and all world optical glass is coming from Kodak and Leitz Research labs.
Mustafa Umut Sarac