共查询到18条相似文献,搜索用时 109 毫秒
1.
2.
基于临床实例的影响蒙特卡罗程序MCNP计算精度和速度的若干参数模拟研究 总被引:1,自引:0,他引:1
蒙特卡罗方法是目前最精确的剂量计算方法,但其较长的模拟时间阻碍了它在临床治疗中的应用。基于蒙特卡罗程序MCNP4c,针对一临床头部病例,探讨了记数方法、电子和光子截断能、光子产生次级电子参数ENUM对计算速度和精度的影响,给出了在保证一定精度前提下的最佳计算模式,以获得计算速度的有效提升。Monte its long simulation and photons, and investigated based Carlo method is regarded as the most accurate method for dose calculation at present, whereas time hinders its clinic application. The effects of the tally method, the cut-off energy of electrons the secondary electron number parameter ENUM on precision and speed of MCNP4c have been on a clinical case to seek for a relatively optimum calculation mode. 相似文献
3.
介绍了具有自主知识产权的蒙特卡罗(MC)粒子输运程序JMCT的初步研制成果。JMCT基于三维组合几何支撑软件框架JCOGIN,采用模块化,分成多层管理结构,可处理多群碰撞和连续能量碰撞,可进行粒子并行和区域分解并行两种并行方法,并具有良好的可扩展性和高速通信技术,同时配有可视化建模前处理软件。介绍了JMCT采用的多群物质碰撞机制,展示了程序模拟计算测试模型的结果,与MCNP程序计算结果一致。JMCT串行计算速度相比MCNP提高了约3 倍;在20 480个处理器核上模拟2109样本,并行效率可达70%。 相似文献
4.
5.
6.
采用蒙特卡罗程序MCNP建立物理模型,对井型高纯锗探测器的效率进行虚拟刻度。模拟计算在密度为0.4,1.2 gcm-3的6种不同成分环境样品中,探测器对射线的探测效率,当能量高于0.10 MeV时,体源样品的探测效率主要与样品密度、射线能量相关。以土壤、水和植物油样品为代表,结合所选取的函数模型,确定了密度范围0.1~1.6 gcm-3的固体源、密度1.0 gcm-3的水溶液和密度0.92 gcm-3的油溶液体源的效率函数及参数。实验采用标准源,对探测效率模拟结果进行了验证,探测效率的模拟值与实验值符合较好,二者误差均在3%以内。说明MCNP程序可以较为准确地模拟计算井型高纯锗探测器对射线的探测效率,验证了该无源效率刻度方法的准确性和可行性。 相似文献
7.
8.
在反应堆上进行中子残余应力谱仪(RSND)的建设工程中,生物屏蔽是降低谱仪测量本底,保证工作人员安全的主要技术手段。为了对屏蔽系统进行优化设计,采用蒙特卡罗方法对其进行模拟计算。采用McStas和MCNP5两种计算程序,理论分析提高计算效率的方法和技巧,并分三步进行谱仪辐射场的计算。首先用McStas程序模拟热中子在导管中的输运过程,然后用MCNP程序计算了屏蔽块之间接合处的拼缝对谱仪辐射场的影响,最后建立整个谱仪屏蔽系统的MCNP模型,并进行计算。将经过用影响因素修正后的计算结果与现场剂量仪实测值进行比较,结果表明二者在允许的误差范围内基本一致。 相似文献
9.
MCNP程序是由美国Los Alamos国家实验室研制的一个大型、多功能的粒子输运蒙特卡罗程序,可计算任意三维复杂几何系统内的中子、光子、电子或中子-光子-电子耦合输运问题,还可计算临界系统的多种本征值问题。MCNP程序的用户遍及全球,国内用户保守估计也在百家以上,过去主要应用在核科学领域,如今已推广到包括医学在内的许多领域。由于蒙特卡罗计算具有数据独立、循环粒度大、负载均衡的特性。因此,很适合作并行计算。虽然从MCNP-4A程序开始,MCNP程序具有了PVM并行计算功能,但并行系统的开发一直存在这样那样的问题,以致无法正常运行。由于MCNP程序有巨大的计算需求和计算量,我们每年使用MCNP程序完成的计算量就超过万CPU小时。许多问题采用串行计算,时间周期太长。因此,迫切需要研究缩短计算周期的并行程序。 相似文献
10.
采用蒙特卡罗方法, 运用MCNP4C程序研究了碳化硼含量20%–40%、中子能量200 eV–15 keV、材料厚度0.3–2 cm对B4C/Al复合材料中子屏蔽性能的影响. 结果表明: 碳化硼含量与中子透射系数呈一次线性下降关系; 同含量的碳化硼, B4C/Al材料的中子屏蔽效果要大大优于聚乙烯碳化硼材料; 在等厚度条件下, 模拟试样B20等的中子屏蔽效果要优于水、铜、混凝土等常规屏蔽材料; 材料厚度与中子透射系数呈指数下降关系, 且单位厚度的增加对中子透射系数改变很大; 含硼量对热中子透射系数影响很大; 在热中子能区, 中子每单位能量的变化对中子透射系数改变较大; 在慢中子能区, 中子每单位能量的变化对中子透射系数改变很小.
关键词:
中子透射系数
蒙特卡罗
铝基复合材料
碳化硼 相似文献
11.
12.
13.
14.
Mohamed Bencheikh Abdelmajid Maghnouj Jaouad Tajmouati Abdessamad Didi Ahad Olah Ezzati 《Physics of Particles and Nuclei Letters》2017,14(5):780-787
The Monte Carlo model for the photon-beam output from the Varian Clinac 2100 linear accelerator was validated to compare the calculated to measured PDD and beam dose profiles The Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy. The objective of this study is to build a Monte Carlo geometry of Varian Clinac 2100 linear accelerator as realistically as possible. The Monte Carlo codes used in this work were the BEAMnrc code to simulate the photons beam and the DOSXYZnrc code to examinate the absorbed dose in the water phantom. We have calculated percentage depth dose (PDD) and beam profiles of the 6 MV photon beam for the 6 × 6 cm2, 10 × 10 cm2 and 15 × 15 cm2 field sizes. We have used the gamma index technique for the quantitative evaluation to compare the measured and calculated distributions. Good agreement was found between calculated PDD and beam profile compared to measured data. The comparison was evaluated using the gamma index method and the criterions were 3% for dose difference and 3 mm for distance to agreement. The gamma index acceptance rate was more than 97% of both distribution comparisons PDDs and dose profiles and our results were more developed and accurate. The Varian Clinac 2100 linear accelerator was accurately modeled using Monte Carlo codes: BEAMnrc and DOSXYZnrc codes package. 相似文献
15.
Andreas Baumgartner Christian Hranitzky Hannes Stadtmann Franz Josef Maringer 《Radiation measurements》2011,46(6-7):595-601
Photon fluence spectra of the Seibersdorf Labor/BEV Picker 60Co therapy unit were calculated using two generally recognised Monte Carlo codes, PENELOPE-2006 and MCNP5. The complexity of the simulation model was increased in three steps (from a pure source capsule and a simplified model using rotational symmetry to a realistic model of the facility). Photon fluence spectra of both codes generally agree within their statistical standard uncertainties for the case of identical geometry set-up and particle transport parameter settings. Resulting total fluence values were about 0.3% higher for MCNP as compared to PENELOPE. The verification of the simulated photon fluence spectra was based upon depth–dose measurements in water performed with a PTW 31003 ionisation chamber and a thick-walled chamber type CC01. The depth–dose curve calculated with PENELOPE agreed with the curve obtained from measurements within 0.4% across the available depth region in the 30 cm × 30 cm × 30 cm water phantom. The comparison of measured and simulated beam quality indices (TPR20,10) revealed deviations of less than 0.2%. 相似文献
16.
Monte Carlo (MC) codes for neutron transport calculations such as MCNP, MCNPX, FLUKA, PHITS, and GEANT4, crucially rely on cross sections that describe the interaction of neutrons with nuclei. For neutron energies below 20 MeV, evaluated cross sections are available that are validated against experimental data. In contrast, for high energies (above 20 MeV) experimental data are scarce and, for this reason, every neutron transport code is based on theoretical nuclear models to describe interactions of neutrons with nuclei in matter. Here we report on the calculation of a complete set of response functions for a Bonner spheres spectrometer (BSS), by means of GEANT4 using the Bertini and Binary Intranuclear Cascade (INC) models for energies above 20 MeV. The recent results were compared with those calculated by MCNP/LAHET and MCNP/HADRON MC codes. It turns out that, whatever code used, the response functions were rather similar for neutron energies below 20 MeV, for all 16 detector/moderator combinations of the considered BSS system. For higher energies, however, differences of more than a factor of 2 were observed, depending on neutron energy, detector/moderator combination, MC code, and nuclear model used. These differences are discussed in terms of neutron fluence rates measured at the environmental research station (UFS), “Schneefernerhaus”, (Zugspitze mountain, Germany, 2650 m a.s.l.) for energies below 0.4 eV (thermal neutrons), between 0.4 eV and 100 keV (epithermal neutrons), between 100 keV and 20 MeV (evaporation neutrons), and above 20 MeV (cascade neutrons). In terms of total neutron fluence rates, relative differences of up to 4% were obtained when compared to the standard MCNP/LAHET results, while in terms of total ambient dose equivalent, relative differences of up to 8% were obtained. Both the GEANT4 Binary INC and Bertini INC gave somewhat larger fluence and dose rates in the epithermal region. Most relevant for dose, however, those response functions calculated with the GEANT4 Bertini INC model provided about 18% less neutrons in the cascade region, which led to a roughly 13% smaller contribution of these neutrons to ambient dose equivalent. It is concluded that doses from secondary neutrons from cosmic radiation as deduced from BSS measurements are uncertain by about 10%, simply because of some differences in nuclear models used by various neutron transport codes. 相似文献
17.
The growth rates of edge-on lamellar polymer crystals in variable thickness films were investigated in terms of dynamic Monte Carlo (MC) simulations. The growth rates linearly decreased with decreasing film thickness for the thinner films and were nearly constant for the thicker films. The mean stem lengths (crystal thickness) were also constant in different thickness films. The crystal widths parallel to the film thickness increased more slowly with increasing film thickness in the thinner films than that in the thicker films, indicating they were restrained by the film thickness. We propose that the growth rate of edge-on lamellar crystals in thin films is dominanted by the crystal width in the thinner films and by the crystal thickness in the thicker films; the variation of the film thickness can change the three-dimensional shape of the crystal growth front, also affecting the growth rate of the edge-on lamellar crystal. 相似文献
18.
全身计数器用于对人体内照射污染的监测,对最小探测活度(MDA)有较高的要求。为使全身计数器具备较好的灵敏度,需要降低本底辐射和提高射线探测效率。基于MCNP5模拟了全身计数器中NaI探测器在不同几何位置时的能量响应,对探测器位置及准直器角度进行研究,同时对不同厚度的屏蔽结构进行了仿真计算分析。研究表明,当屏蔽钢板厚度为14.9 cm时,能够较大程度地降低本底辐射。在源探结构上探测腔准直器角度在26以上,探测器与体模的距离为20 cm时,能够得到理想的能谱响应和探测效率。 相似文献