National Lead Shielding Computer (1960s)

Manufactured by the National Lead Company, the purpose of this slide rule is to determine the thickness of lead required to reduce the exposure rate at one meter from a gamma emitting point source to 5 mR/hr. Given the manufacturer of this device, you might suspect that the required amount of lead was overestimated a bit ;-). 

To operate, the fine line running down the middle of the pivoting pointer is lined up with the intersection of the most appropriate curve for the source activity (0.01 to 10,000 Ci) and the most appropriate line for the gamma ray energy (0.3 to 3.0 MeV). The required thickness of lead is then read off the scale at the tip of the pointer. The back of the "computer" indicates the gamma ray energies for a variety of radionuclides.

For the sake of full disclosure, it must be admitted that there is no slide to this "slide rule."


There is no obvious date on the calculator (or the cardboard holder), but it is stamped F-100-60 which suggests that 1960 was the first year that the "computer" was produced.

Kindly donated by Tom Clark

Size: 3.75" x 10" (laminated cardboard)

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Last updated: 05/10/11
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