Evaluation of Structural Shielding Designs of X-Ray Linear Accelerator Scanner at the Port of Tema, Ghana

This study was conducted to evaluate the shielding designs of a 6 MeV x-ray linear accelerator scanner used for cargo-container scanning at the port of Tema in Ghana. Workload of the facility had increased significantly over time necessitating review of the installed shielding. There had been introduction of x-ray unit with higher energy (from 5 MeV to 6 MeV) increasing absorbed dose per scan. The number of scans per day had increased from an average of 60 to 95 scans. New structures had been built around the facility without particular attention to their distances and orientations with respect to the radiation source. The principle that the product of the weekly time average dose rates (Rw) and the occupancy for a particular point of interest (location) should not exceed the design dose limit, P (i.e. P ≥ RwT) for that location was partly used to determine the adequacy of the shielding afforded by the barriers. In addition to P ≥ RwT, calculated and measured hourly time average dose rates (Rh) were used to establish the adequacy of the shieldings based on the dose limit of 0.5μSv/h for public and supervised areas (uncontrolled areas). The Rw, calculated Rh and measured Rh all fell below the dose limit showing that the primary and secondary barriers are adequate.