Radiac detector DT-60/PD is a non-self-indicating personnel dosimeter which is worn about the neck like a pendant. The sensitive element is a radiophotoluminescent glass which emits luminescent light under near ultra-violet irradiation after prior exposure to X or gamma radiation. Translation: This Cold-War beauty shows you just how fried you are after a radiation exposure. These are sold individually with a set of original instructions and specifications. Dated 1951 and manufactured by the Polaroid Corporation. 1 1/2" x 3/8" thick.