Angular Response Functions for Sodium Iodide Detectors

This paper presents analytical, Monte Carlo and experimental investigations on the angular response functions to gamma sources of typical cylindrical scintillation detectors. A general analytical approach capable of computing the total counting efficiency of geometrically-simple detectors to isotropic point sources is introduced. MCNP5 calculations are performed for several cylindrical NaI(Tl) detectors with different sizes in order to verify this analytical approach. Photopeak efficiency is also computed based on analytically determined total counting efficiency and MCNP5 calculated peak-to-total ratio. Sets of angular measurements are executed for cylindrical NaI detectors of different sizes using Cs-137 and Co-60 sources with appropriate radioactivity. The three means of determining the angular response functions for the total efficiency and photopeak efficiency give consistent results with less than 5% discrepancy over the measured range.