Identifying Radioisotopes in Soil Samples of Lake Norman*

We are constantly exposed to radiation from naturally existing radioisotopes, but human activity can artificially introduce radioisotopes too. Lake Norman, located near Davidson College, has both coal and nuclear power plants. Improper management of waste products from these plants can deposit potentially harmful isotopes into the environment. Thus, the radioisotopes present and their activity were analyzed to evaluate the lake’s radioactivity. To identify and calculate the activity of radioisotopes present, soil samples were collected across the lake. The radioactive content in the samples were analyzed using gamma ray spectroscopy, specifically using two NaI detectors to conduct coincidence gamma ray spectroscopy. Coincidence spectroscopy only classifies events where two or more gamma rays emitted within a short time frame. This procedure reduces background radiation, and allows for clearer identification of emitted gamma rays. Single emissions were also recorded to calculate the activity of identified radioisotopes. From the analysis of 9 soil samples, it was observed that all samples emitted gamma rays of specific energies from isotopes of the decay chains of Th-232 and U-238, but alpha spectroscopy would be needed to confirm the presence of the two isotopes.