A Case Study about Counting Uncertainty of Radioactive Iodine (131I) in Public Waters by Using Gamma Spectrometry

The radioactive iodine ( 131 I) presents in the environment through the excrete process of nuclear medicine patients.In the detecting of low level of 131 I in the public water, the counting uncertainty has an effect on the accuracy and reliability of detecting 131 I radioactivity concentration.In this study, the contribution of sample amount, radioactivity concentration and counting time to the uncertainty was investigated in the case of public water sample.Sampling points are public water and the effluents of a sewage treatment plant at Sapkyocheon stream, Geumgang river.In each point, 1, 10 and 20 L of liquid samples were collected and prepared by evaporation method.The HPGe (High Purity Germanium) detector was used to detect and analyze emitted gamma-ray from samples.The radioactivity concentration of 131 I were in the range of 0.03 to 1.8 Bq/L.The comparison of the counting uncertainty of the sample amount, 1 L sample is unable to verify the existence of the 131 I under 0.5 Bq/L radioactivity concentration.Considering the short half-life of 131 I (8.03 days), a method for measuring 1 L sample was used.However comparing the detecting and preparing time of 1, 10 L respectively, detecting 10 L sample would be an appropriate method to distinguish 131 I concentration in the public water.