Determination of self-attenuation correction factors for 3′′×3′′ NaI(Tl) detector by using Monte Carlo Code FLUKA

Abstract

NaI(Tl) gamma spectroscopy systems are widely used to determine the radioactivity level of the environmental samples. It is important to calculate the correct activity of environmental samples with respect to the calibration source. An activity correction is required when the density or absorption coefficient of the calibration source and the environmental sample is different; this is called the self-attenuation correction factor. In this study, the $3^{\prime \prime }\times 3^{\prime \prime }$ NaI(Tl) gamma spectroscopy system in our laboratory was modeled using the Monte Carlo code FLUKA. Simulation results were validated by comparing the experimental and simulation FWHM results both for disk sources alone and disk sources placed above the 1 L Marinelli beakers. Self-attenuation correction factors were calculated for 0.5 and 1 L Marinelli beakers in the $238.6\text{-}2614$ keV energy range using the FLUKA code. The materials in Marinelli beakers are assumed to be air, water and ${\mathrm{SiO}}_2$ in FLUKA simulations, the densities of these materials range from 0 to 2.8 $g/{\mathrm{cm}}^3$. Additionally, energy and material density dependent coefficients of the analytical self-attenuation correction factor equation for 0.5 and 1 L Marinelli beakers were also derived using the FLUKA results.