Emanation from Granite Countertops

Emanation of radon ( 222 Rn) from granite countertops was measured using continuous and integrating radon monitors, and in air collected from encapsulated pieces of the countertops. A majority of the countertops emitted a measurable amount of radon. Although the granites contained the precursors, no thoron ( 220 Rn) emanation was detected. Gamma-ray spectroscopy was used to determine amounts of radium ( 222 Rn precursor) and other radionuclides in the granites. There was a correlation (r 2 =0.50) between the measured radon emanation and the radium content of the granites. Based on gamma-ray spectroscopy results, radon-emanation losses from the granite samples averaged 26% of the total radium concentrations. Although some granite countertops emitted substantial amounts of radon (range= <0.1 2.3 pCi/L), the contribution to indoor radon concentrations was estimated to average 0.6 pCi/L.