New analytical approach to calculate the detector efficiencies of NaI(Tl) using coaxial and off-axis rectangular and parallelepiped sources

In this paper, we introduce a direct analytical mathematical method for calculating the geometrical and absolute total efficiencies of gamma-ray NaI(Tl) scintillation detectors using coaxial and off-axis plane (rectangular) sources. The calculations of geometrical and absolute total efficiencies of coaxial and off-axis plane (rectangular) sources are extended to include coaxial and off-axis volumetric (parallelepiped) sources. The current theoretical and the published efficiency values are in good agreement.