Concrete-filled pit, 4 ft in diameter, with three 8-ft beds penetrated by a 5 1/2-in. hole cased with 17-lbm casing.

The top and bottom beds are composed of extremely-low-radioactivity concrete.

The middle bed was made approximately twice as radioactive as a typical midcontinent US shale, resulting in the zone containing 13 ppm uranium, 24 ppm thorium, and 4% potassium.

where

 is GR tool reading against radioactive part of Calibration Stand

 is GR tool reading against non-radioactive part of Calibration Stand