VARIATIONS IN RADON PRODUCTION OF THE PETERSBURG GRANITE NEAR RICHMOND, VA

Radon gas is the second leading cause of lung cancer worldwide. To inform the public of the risks of radon exposure, the EPA created a radon risks map in 1993 which defines the radon risk of different Virginia counties as low, moderate, and high. The map assesses risk level based approximately on geologic provinces, but radon emanation levels vary greatly within the Virginia geologic provinces. The boundary between the Coastal Plain and the Piedmont changes abruptly from low risk in the Coastal Plain to high risk in the Piedmont. In an effort to enhance the scale of the EPA risk map and better inform the public of the risks, this study aims to investigate the radon emanation levels and uranium levels of the major geologic unit separating these two provinces: the Petersburg Granite. The Petersburg Granite consists of four major subunits— the subidiomorphic or massive granite, porphyritic granite, foliated granite, and granitic gneiss—each with varying Zr compositions, which we believe may be a cause of the variability in radon emanation levels due to U-Zr substitutions. We measure the radon emanation of rock and saprolite samples from each of these subunits using a Durridge Rad7 radon detector. Based on emission chamber results from the Rad7 detector, we find that the unit with the highest radon emanation is the massive granite reaching 65.1 pCi/L and the saprolite samples reaching 102.9 pCi/L. We also analyze these samples for ²³⁸U and ²²⁶Ra using gamma spectrometry and Zr using x-ray fluorescence spectrometry. This research stands to improve our prediction of the radon emanation levels in central Virginia in order to better inform the public about the associated health hazards.