Gamma Ray Calibration Stand in University of Houston

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.

$//<![CDATA[ \begin{array}{l}1 \ {\rm GAPI} = 0.005 \cdot (GR_{RA} - GR_{NRA})\end{array} //]]>$

where

$//<![CDATA[ \begin{array}{l}GR_{RA}\end{array} //]]>$ is GR tool reading against radioactive part of Calibration Stand

$//<![CDATA[ \begin{array}{l}GR_{NRA}\end{array} //]]>$ is GR tool reading against non-radioactive part of Calibration Stand