关键词: 粒子输运, 复杂几何, 直接 CAD 法, 包围盒

Abstract: Many traditional Monte Carlo transport programs use the Constructed Solid Geometry (CSG)method for modeling, which is time-consuming and labor-intensive for complex geometries. Therefore, it is necessary to find a method that can simplify the neutron modeling process. This paper explores the key technologies for Monte Carlo transport directly on the CAD model, such as geometric data structure, particle-solid collision algorithms, and the search for the next entity algorithm. Based on these technologies, a preliminary usable direct-method transport program was developed. Moreover, the bounding box acceleration algorithm was introduced to speed up the computation process. The geometric algorithm was validated by a simple model and compared with cosRMC. The results show that the direct method program agrees well with the cosRMC results,which confirms the correctness of the geometric algorithm. The direct method also demonstrates its advantages of high accuracy, intuitive display, and wide applicability by calculating the neutron flux on the surface of the human body model.

Key words: Particle transport, Complex geometry, Direct CAD, Bounding box