TULSA — A University of Tulsa spokeswoman says school officials were "blindsided" when they learned that a small, radioactive chemical spill occurred last fall at college's north research campus.

She says researchers involved in a project with oil and gas services company Tracerco spilled the radioactive isotope cesium-137 in the Process Building, but school officials didn't learn about it until last week. The joint industry project is managed by the university's Petroleum Engineering Department.

Officials say at least 21 people will be evaluated for potential exposure to the chemical. Cesium emits two types of radiation — beta particles and gamma rays — that have enough energy to damage human tissue.