Estimation of self-absorption correction factors for gamma-ray spectrometry of radioactive waste using MCNP

Abstract

Gamma-ray spectrometry is a suitable technique for the radiological characterization of radioactive waste. However, differences in material and density between certified reference materials (CRMs) serve as standards for calibration. The waste sample can cause self-absorption effects, necessitating appropriate corrections. This study presents a practical method for deriving self-absorption correction factors using MCNP6.2. A detailed detector model and measurement setup were constructed in MCNP6.2 and optimized by comparing simulation results with experimental measurements. Three different CRM geometries were employed to improve modeling accuracy. Simulations were refined across three HPGe detectors within 59.54-1836.05 keV energy range to achieve average and maximum deviation between simulated and measured FEPE (full energy peak efficiency) of 1.9 +/- 2.16 % and 4.9 +/- 1.9 %, respectively. Using the optimized MCNP inputs, self-absorption correction factors were calculated with densities ranging from 0.1 to 8.0 g/cm3. Additionally, the corresponding equations for effective path lengths were determined for specific geometries. The self-absorption effects were further evaluated for combustible, incombustible, and metallic waste over the same density range. The correction factors were derived and compared by material type. The validity of the proposed method was experimentally confirmed using concrete-based CRM. The results will improve accuracy and efficiency in sampling and activity concentration analysis in radioactive waste management.