ORNL Ring Film Badge (ca. 1950-1955)

ORNL film dosimeter
ORNL film dosimeter

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."

ORNL film dosimeter

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.

Reference

Morgan, K.Z., unpublished mauscript, “Health Control and Nuclear Research,” ca. 1952.