MC Simulation Of Medical X-ray And Optimum Design Of Protective Materials

X-ray is widely used in the medical field and its harm to human body can not be ignored.Most of the artificial X-rays are broad beams and the distribution of energy spectrum is relatively complex.Therefore,it is an very important research work to accurately describe the distribution and dose properties of medical X-rays and to select suitable materials to better protect the human body from the harm caused by X-rays.Firstly,the models of medical diagnostic X-ray machines and electron linear accelerators are established by using Monte Carlo software MCNP5,and their energy spectrum characteristics and dose distribution are investigated.In order to better filter diagnostic X-rays,the commonly used filtering materials for medical diagnostic X-rays were investigated,the transmittance of various materials to X-rays in different energy segments was calculated,and their filtering effects were comprehensively compared.Then select suitable rare earth elements to shield low-energy X-rays,and use BP neural network algorithm combined with genetic algorithm to establish an optimization model to calculate and obtain the optimal ratio of composite materials.The main research work and achievements of this paper are summarized as follows:?1?By Monte Carlo method,the models of medical X-ray machines and medical electron linear accelerators are first established by MCNP to simulate medical diagnostic X-rays and therapeutic X-rays produced by electron targeting,and then the characteristics of medical diagnostic X-rays are analyzed.It is found that the characteristic X-rays in the diagnostic X-ray spectrum only account for a small proportion,the number of particles at the low energy end will be greatly reduced after collimation and filtering;The energy spectrum distribution law of 6 MV X-rays and the dose distribution information in the water model a 100 cm SSD are studied.The results show that the energy spectrum of 6 MV X-rays is dominated by bremsstrahlung with a peak value of 0.7 MeV.After collimation and leveling,the deposition dose at the depth of 1.51 cm in the water model reached the maximum,which was basically the same as the measured values given in the literature.?2?According to the physical characteristics of X-rays,the filtering materials for diagnosing X-rays were initially screened,and the filtering effects of different materials on different energy segments of X-rays were investigated.It was found that when metal Ni was used as the filtering material,it could not only absorb most of low-energy particles,but also transmit most of high-energy X-rays,with the best comprehensive effect.?3?As a commonly used diagnostic X-ray shielding material,Pb has a"weak absorption region".Four of the five rare earth elements La,Ce,Pr,Gd and Sm with K absorption edge in the energy range of tungsten characteristic peak are selected to be combined to obtain five compositions,and the mass attenuation coefficient of the composite materials within 100 keV is calculated by WinXCom software.The results show that the K absorption edge of the selected material is in the characteristic peak region of medical diagnostic X-ray,and the weak absorption region of the material can be compensated by the matching of K absorption edges.?4?Using genetic algorithm and BP neural network algorithm,the optimization model is established,and the optimal combination ratio of five kinds of composite materials is calculated and verified by MCNP program.It is Reasonable to conclude that the material combination Ce₂O₃-Pr₂O₃-Sm₂O₃-Gd₂O₃ has better comprehensive performance than the other four combinations.According to the calculation,the optimal combination ratio is?0.36:0.29:0.23:0.12?.When the thickness is 0.18 cm,99.99%of the radiation can be shielded,and its density is only 61.7%of that of lead,proving the accuracy of the optimized calculation results.