RADIOACTIVITY OF VOLCANIC SEDIMENTS IN BRAZOS COUNTY, TEXAS

Abstract

The relation between the field unit of gamma radiation intensity, microroentgen per hour, and the laboratory units, expressed in concentration of radioactive elements, was determined by measuring the radiation intensity over a level rock surface and measuring the gamma radioactivity of the same rocks in the laboratory. The available data indicate that one percent potassium equivalent of gamma radioactivity is [Formula: see text] radium equivalents, [Formula: see text] potassium equivalents, [Formula: see text] thorium equivalents, and produces a gamma radiation intensity of 0.57 microroentgen per hour over a flat surface. Measurements of volcanic sediments of Upper Eocene and Miocene age in Brazos County, Texas, show gamma‐ray emissivities of 4.5 to 10.9 percent potassium equivalents of gamma‐ray emissivity. This is about the same as ordinary shales. The mixture of volcanic particles with clastic sediments in these samples suggests that the radioactivity of the original volcanic matter may possibly have been reduced by weathering.