Radon Daughter Slide Rule (ca. 1970s)

This slide rule was developed by Robert Beckman at the U.S. Bureau of Mines Technical Support Center in Denver Colorado in the 1970s. One side is a standard slide rule. The other side (shown below) calculates the radon daughter concentration in working levels (WL).

It was used to simplify the calculations in the Kusnetz (and Rolle) method for determining the radon daughter concentration. An air sample would be pulled for five minutes and after at least a 40 minute wait, an alpha count (e.g., one minute or longer) would be performed on the filter. The index on the top slide would be lined up with the efficiency factor determined for the detector (the inverse of the decimal efficiency). The volume of the air sample on the middle slide would then be lined up with the elapsed time between sampling and counting on the top slide. The working level concentration on the bottom scale would then line up with the observed count rate (cpm) on the middle slide. Pretty slick!

Size: ca. 1.5" x 12.5"

Donated by Robert Beckman.

Reference

Robert T. Beckman and Robert L. Rock.  Radon-daughter slide rule. Mining Enforcement and Safety Administration, IR 1003. 1974.