Radioactive Lenses

Quite a few vintage lenses from the 40s until the 70s contain radioactive Thorium Oxide in one or more elements, so I bought myself a Geiger-Müller counter to check the lenses I own to facilitate proper storage.

At the time of writing, I own the following vintage lenses. According to the internet, only the Takumar 50mm is likely to contain any traces of Thorium Oxide.

• Pentax Takumar 50mm f/1.4
• Pentax Takumar 135mm f/2.4
• Pentax Takumar 300mm f/4
• RMC Tokina 35-105mm f/3.5 Macro

I tested them all just to be sure, but as expected, only the Takumar 50mm showed any sign of radioactivity, which is good, since I often travel with the 135mm and 300mm for astrophotography.

GQ GMC-300E

While Thorium Oxide produces alpha, beta, and gamma radiation, the GQ GMC-300E Geiger-Müller Counter I've used here only detects beta and gamma. My goal is, however, only to produce a boolean answer if my lenses are radioactive or not, and for that, this device is more than capable.

You should watch this video to learn more about radioactivity in vintage lenses from a person more qualified than me. It is really interesting!

Pentax Takumar 50mm f/1.4

Raw measurements of Countes Per Minute (CPM) and uSv/h for the Pentax Takumar 50mm f/1.4, taken from various angles, distances, and obstructions, can be found below.

Background radiation was measured at 30CPM, or 0.19uSv/h.