Yes, from
Takumar - Camera-wiki.org - The free camera encyclopedia
Asahi used Thorium oxide in the production of optical glass in several Super-Takumar, Super-Multi-Coated, and even in a few SMC-Takumars between 1964 and 1973. In these lenses usually only one element of this glass was used, either in front or in the back. The drawback is that thoriated glass tends to discolor over time, to a yellow-brown color which can be reversed by the action of photons (bright light) and UV light.
[18] The discoloration also reduces the brightness of the lens, to the point that it might lose 1/2 to 3/2 stops. Many users have proven that exposing the yellowed lenses to sunlight for a few days, UV light or even a bright LED light will clear the lens element.
Notable lenses that have this kind of glass are: Super- and Super-Multi-Coated Takumar 50mm f/1.4 (7 element version), 20mm f/4.5, 35mm f/2, 55mm f/1.8, 55mm f/2 and 85mm f/1.8. Super Takumar 6x7 105mm f/2.4.
Fortunately most of the residual radiation is Alpha-type and is not dangerous and will not fog the film.
[2] Studies carried out by the US Army show that glass attenuates alpha radiation and any residual will be absorbed in a surface layer of less than 100 micrometers.
[19]
