The paramagnetic radicals formed in the TL phosphors BaSO4:Eu and BaSO4:Eu, P have been studied using the technique of ESR. Two radicals assigned to SO2-, were observed at room temperature. One of them exhibits a hyperfine interaction with a nearby cation. Step annealing measurements suggest a connection between these radicals and the TL glow peaks at 170 and 215 degrees C. Co-doping BaSO4:Eu with phosphorus enhanced its TL efficiency. ESR and fluorescence emission measurements indicate that the enhancement results from an increased intake of divalent europium into the lattice.