Selection of calculation modes in nuclear shielding material optimization.

Optimizing the shielding material via intelligent optimization algorithms has become a tendency in recent years. This study investigated the calculation modes used in the optimization. Two modes are presented in this study. Mode A optimizes the shield with a variable thickness, the result optimized is exactly the desired result. It is suitable for the application that only need material with small thickness (less than several mean free paths), such as compact systems or mobile devices. Mode B optimizes the shield with a fixed thickness, the optimized result is just an intermediate solution, and the final result needs to be extrapolated. It could be applied to optimize the material whose thickness needed is comparatively larger. Several materials were optimized using the two modes, and comparisons among the materials were made. It is found that, the material properties optimized by the two modes are basically the same, and the thickness should be set at about 10 mean free paths of neutrons in those materials when the mode B is adopted.