ORNL Ring Film Badge (ca. 1950-1955)
This ring badge was developed at Oak Ridge National Laboratory and manufactured by the Patent Button Company of Knoxville, Tennessee. The film (DuPont 502) is sandwiched between two 1 mm thick cadmium disks with a small hole in their centers. The plastic screw-on cover is sufficiently thin (ca. 0.5 mm thick) that the center of the film will respond to betas as well as gamma rays and X-rays. The following is written on the perimeter of the ring cover: "Hand Exposure Meter – O.R.N.L. – A.E.C."
The film itself is energy independent above 200 keV or so. In other words, the measurements will be accurate above this energy. From 50 to 200 keV the film over-responds, and below 5 keV it under-responds. The purpose of the cadmium disk is to reduce the over-response to low energy photons. The problem is that the cadmium also eliminates the very lowest energy photons. Hence the hole: to allow enough low energy photons through to the film to compensate.
Donated by Ron Kathren.
Morgan, K.Z., unpublished mauscript, “Health Control and Nuclear Research,” ca. 1952.