NPTS程序质子输运蒙特卡罗模拟方法研究

Study of Monte Carlo Simulation Method for Proton Transport in NPTS Program

  • 摘要: 带电粒子输运蒙特卡罗模拟程序广泛应用于放射治疗、辐射防护、加速器设计等领域。国内中子、光子蒙特卡罗模拟程序发展较为成熟,但具备带电粒子输运模拟功能的程序较少。本文应用带电粒子输运连续慢化理论、多重散射理论及能量岐离分布模型,建立了重带电粒子蒙特卡罗模拟方法与框架。应用ENDF/B-Ⅶ.0核数据库模拟带电粒子核反应,基于蒙特卡罗程序NPTS(neutron-photon transport simulation program)研制了质子输运模块,完善了该程序质子、中子、光子、电子等多粒子耦合输运功能。基于厚靶模型、质子治疗室模型考察了NPTS程序质子、中子耦合输运计算的准确性。结果表明,NPTS程序在计算中子产额、辐射场分布等方面与主流蒙特卡罗程序结果一致,与实验结果符合较好,可有效用于BNCT(boron neutron capture therapy)靶设计、辐射屏蔽分析等带电粒子输运模拟问题。

     

    Abstract: Monte Carlo simulation has become an effective method for solving different physical problems, which is especially advantageous in the particle transport problems with complex geometric models. Charged particle transport simulation programs based on Monte Carlo method are widely used in medical therapy, radiation protection, accelerator design and other fields. Although the domestic neutron and photon transport simulation programs are well developed, there are few programs being able to do charged particle transport simulation. In addition, the energy range for programs based on the intranuclear cascade model and evaporative fission model is usually high, above several tens of MeV. For medium and low energy proton transport, the accuracy of nuclear reaction simulations based on nuclear databases is better than that of models. The biggest problem with Monte Carlo methods for simulating charged particle transport calculations is that the number of collisions of charged particles is too frequent. Therefore, this paper was based on the condensed history method to simulate the proton transport. In this study, with the application of key physical model of charged particle transport, such as the continuous slowing down approximation theory, multiple scattering theory and energy straggling model, a framework of heavy charged particles transport simulation program was established. Based on nuclear database of ENDF/B-Ⅶ.0 proton-nucleus interactions, the proton transport simulation function was implemented on the NPTS (neutron-photon transport simulation program). The extended NPTS program supported the simulation of proton transport problems in the energy range from 1 keV to 150 MeV and multi-coupling transport calculations of protons, neutrons, photons and electrons. A comparison of the stopping power of protons, deuterons and alpha particles in common materials with SRIM was carried out by the NPTS program, which proved the correctness of NPTS in calculating the stopping power of charged particles. The numerical results of neutron yield, average energy and angle for the thick target model agree well with GEANT4, MCNP6 and experimental results. In order to fully verify the program, a proton treatment chamber model with larger spatial dimensions and more complex geometry was used for the study. The neutron flux distribution inside the treatment chamber obtained by NPTS was basically consistent with GEANT4. The accuracy of the NPTS simulations of proton transport and multiparticle coupled transport was verified by several test models. Moreover, the proton energy and continuous slowing down approximation range curves obtained from the NPTS calculations can be used to quickly estimate the target thickness at maximum neutron yield, providing a favourable reference for BNCT (boron neutron capture therapy) target design. This paper effectively extends the application of the NPTS program in accelerator target design, shielding analysis, and radiation protection. The research effectively improves the application value of NPTS program, as well as enriching the research method of medium and low energy proton transport programs in domestic.

     

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