Khairi M.S. Abdullah Department of Water Resources, College of Engineering, University of Duhok, Iraq khairi_ms51@yahoo.com International Journal of Fundamental Physical Sciences (IJFPS) 5 2 32-37 June, 2015 2231-8186 https://doi.org/10.14331/ijfps.2015.330083 Due to the poor resolution of NaI scintillation detectors, spectral interferences occur between 137Cs and 214Bi, causing overestimation in activity concentrations. This paper presents a correction methodology for the NaI(Tl) detector system to accurately resolve overlapping peaks. The approach was validated using environmental samples from Duhok, Iraq, affected by fallout from nuclear activities and Chernobyl. The method reduced relative errors in 214Bi activity measurements significantly, demonstrating its accuracy and applicability. It may be extended to other detector configurations and overlapping peak cases. Doublet peak area, Environmental radioactive sources, NaI scintillation spectroscopy, Cesium-137 https://creativecommons.org/licenses/by/4.0/