| Radiation safety is one of the key concerns in the field of nuclear technology applications.Gamma rays have become the main protection object considered in radiological practice due to their strong penetrating ability and great damage to biological tissues.The PointKernel method is widely used in gamma dose estimation due to its high computational efficiency,and the buildup factor is a key parameter that determines the accuracy of the point kernel method,and represents an estimate of the scattered photon dose share.In this paper,a method for calculating γ-ray buildup factors based on Monte Carlo simulation(MCs)and Extremely Randomized Trees was proposed,aiming to achieve efficient and accurate calculation of buildup factors.The main contents are as follows:(1)According to the latest photon interaction cross section library,various physical processes including coherent scattering and bremsstrahlung radiation was considered,the MCNP program was used in conjunction with the narrow beam attenuation law to calculate the exposure buildup factors,a new buildup factor database EBFMC for various materials under different γ-ray energies and different shielding thicknesses was established,analyzed the data rules,and compared the data with that in the ANS standard library;(2)Based on the Extremely Randomized Trees(ET)algorithm,a regression model ETB suitable for EBFMC data was established.The model was tested with respect to energy,shielding thickness,and atomic number of the material,and the calculation efficiency of the model was examined to preliminarily verify its feasibility;(3)A new method for calculating the atomic number of the equivalent layer of the double-layer shielding was proposed in this paper,and an iterative model ETML for calculating the buildup factors of multi-layer shielding was established,the accuracy of the model was tested under the three-layer shielding and the four-layer shielding cases,and the computational efficiency of the model was investigated,thus verifying the feasibility of the method.Analysis and tests results show that,compared with the standard library of buildup factors published by the American Nuclear Society(ANS)in 1991,the cross-sectional data used in EBFMC is the latest,and the consideration of the physical process is more comprehensive;Compared with the existing fitting method of buildup factors suitable for point-kernel calculation,the buildup factor regression technique proposed in this paper based on ET has higher accuracy when calculating stratified shields,and it can get good results without complicated parameter tuning process,and it is more convenient to use.At the same time,its efficiency can also meet the requirements of point-kernel calculations.In summary,the research results of this paper can replace traditional empirical formulas to achieve efficient and accurate buildup factor calculations,which can be applied to point-kernel codes and provide more reliable data references for the field of radiation protection. |
