The Isotope Handling Calculator No. 1 was designed by the Isotope Division AERE Harwell England and described in the August 1953 issue of Nucleonics. As far as nuclear slide rules are concerned, this is as good as they get (solid 1/8" plastic).
The purpose of the calculator was to facilitate certain calculations involving the following radionuclides: Na-24, Co-60, Ra-226, Ta-182, Ir-192, Au-198 and I-131. To be specific, it relates the radionuclide source activity (uCi, mCi, or Ci) to the gamma exposure rate (R/hr) at a given distance. It also indicates the safe handling time per day (based on 100 mR/day), and the reduction in the exposure rate due to a specified thickness (cm or inches) of lead shielding. The instructions are indicated on the back side of the calculator (not shown).
Size: 8.5"diameter
References
R. West. Isotope Handling Calculator. Nucleonics August 1953, page 50-52.
R. West. A.E.R.E. Report IR/1063 An Isotope Handling Calculator. 1953.