Gamma spectrum unfolding for a NaI monitor of radioactivity in aquatic systems

Full text: Spectrum unfolding is a powerful method that may enhance clearly the readability of experimental energy spectra obtained by detectors of poor resolution, like scintillators. This technique can be implemented when the angular distribution of the radiation fluence is known. In the case of the system developed by the Institut National des Radioelements for monitoring radioactivity in aquatic systems - a NaI(Tl) detector - the source is an infinite homogeneous medium surrounding the monitor, with constant density. The UMG 3.3 package is used for unfolding the experimental spectra, with the response matrix obtained by the use of MCNP4c2. The main parameter influencing the quality of the results, besides the quality of the acquisition data's, is the adequacy factor χ2. The first step of this study was to optimize the choice of χ2 for both the calculation's time and the accuracy of the process. The second step was to evaluate the global statistical accuracy of the technique. The results of unfolding are presented for both fresh and seawater