Brass and Aluminum Ring Badge (ca. 1950s)
This item is a bit of a mystery. I not only don't know where it came from, I don't know what type of sensing element it used! Including it in the film dosimeters category is simply a guess, and not a very good one at that. What I can say is that the body of the ring is brass and that the cylindrical aluminum holder for the sensing element has six ovoid holes drilled through the screw-in cover. As seen in the photograph below right, the holder contains a single thin aluminum disk.
My guess is that it was designed to hold film although I can't completely rule out the possibility that is was meant to use radiophotoluminescent (RPL) glass or a TLD. The problem with the RPL glass theory is that the latter had poor sensitivity and was primarily used for accident dosimetry. It doesn't make sense to use a ring badge for accident dosimetry. If it was used for film, it is not clear how it would have been kept light-tight—film wasn't available in sealed packets. If it was used with some sort of thermoluminescent material, it is a very primitive design.