Monte Carlo simulation of radioactivity γ-ray spectra recorded by a NaI detector in the marine environment

In the studies of radiological assessment, 137Cs is the most important radioactive contaminant, produced from the atmospheric bomb tests, discharges from nuclear reprocessing plants and the Chernobyl reactor accident. The systems most commonly used for the in situ monitoring of γ-radiation in seawater, are based on NaI(Tl) detectors, which are characterized by high detection efficiency and low cost [1-3]. They have, however, the disadvantage of relatively poor energy resolution and high background mainly originating from the Compton effect during the detection process of the high energy γ-rays from the deexcitation of natural radionuclides, such as 40K and 214Bi [4]. This makes the systems incapable for precise peak identification of the various gamma ray contributions, especially for low level radioactivity studies and in the low energy region, where the 661keV γ-ray of 137Cs, is situated in the spectra.