Gamma Ray Radiographic Slide Rule (ca. 1940s)
This "Gamma-Ray Radiographic Slide Rule" was produced by the Canadian Radium & Uranium Corporation located at 630 Fifth Avenue at Rockefeller Center in New York city. The copyright date (see image below) suggests that it was probably manufactured in the 1940s.
Its purpose was to facilitate the determination of the appropriate exposure times for radiographic operations involvingradium-226 sources. The manner of use, described on the back of the slide rule, is relatively straightforward. The source to film distance (in inches) was positioned next to the source strength of the radium (in mg), and the appropriate exposure time (in hours) was indicated next to the thickness (in inches) of the steel object being radiographed. If the object was not steel, its equivalent steel thickness could be determined using the "alloy section" in the lower right hand corner of the slide rule.
It was intended to apply to the use of "regular radiographic film (not screenless type), exposed with .005" thick lead intensifying screens developed twice normal time in regular X-Ray developer with 20 milligrams of potassium iodide added per liter of developer."
Size: 1 1/8" x 10 3/8"