Secondary electron emission yield calculation performed using two different Monte Carlo strategies

The secondary electron emission yield in Al₂O₃ and polymethylmethacrylate (PMMA) is calculated using two different Monte Carlo approaches, one based on the energy straggling strategy (ES), the other one on the continuous-slowing-down (CSD) approximation. This work is aimed at comparing the secondary electron emission yields calculated by these two Monte Carlo strategies with the available experimental data. The results of both methods are in good agreement with experimental data. The CSD strategy is about 10 times faster than the ES strategy.     

Monte Carlo calculation of electron Rutherford backscattering spectra and high-energy reflection electron energy loss spectra

The electron Rutherford backscattering spectra and high-energy reflection electron energy loss spectra have been calculated by a Monte Carlo method for bulk solids and overlayer/substrate systems. The simulation model is mainly based on the use of Mott cross section for elastic scattering and the use of Penn’s dielectric functional approach to the electron inelastic scattering inside the solid. Moreover, it has further considered the recoil energy loss of energetic electrons and the thermal vibration of atoms with an isotropic distribution of the velocity direction. The calculated energy loss spectra for Al/Pt and Al/Mo agree with the experimental spectra quite well. The signals owing to different kinds of atoms can be separated by taking the scatter for the maximum-scattering angle event along an electron trajectory as the Rutherford backscattering atom, enabling a theoretical estimation of the peak intensity ratio. Furthermore, the simulation has also indicated that the multiple scattering is the dominant process to the quasi-elastic and energy loss of the electrons and is responsible mainly to the difference on the peak intensity between the linear model and experiment.     

Monte Carlo模拟对放疗中电子反散射谱的研究

电子束治疗腮、耳垂等敏感处肿瘤时,经常需要挡铅以保护正常组织,由此产生电子的反散射效应.本文用蒙特卡罗程序模拟了10MeV临床电子束谱随深度的变化;给出了多种散射体的反散射谱平均能量与基本电子谱平均能量的比值随平均束能量的变化曲线.并从能谱的观点,对反散射效应强弱随深度的变化关系作了定性分析,得到与文献一致的结论.     

Monte Carlo simulation of Tabata’s electron backscattering experiments

Electron backscattering coefficients, η, obtained from several targets in the MeV range were calculated by using electron-photon Monte Carlo transport calculation codes, i.e., EGS5 and ITS 3.0. These calculated values were compared with those obtained from the electron backscattering experiment performed by Tabata using an ionization chamber [15]. We found that Tabata’s estimation of the multiplication factor of the ionization chamber, f, had a non-negligible error. Then, we calculated the ionization chamber output, I, which is a product of η and f. The ratios of I between the experimental and the calculated values were within 1.5 and 1.3 for the EGS5 code and the ITS 3.0 code, respectively. The ratios of η between the experimental and the calculated values were within 2.4 and 1.5 for the EGS5 code and the ITS 3.0 code, respectively. The differences between the experimental and the calculated values of I and η are large for low-Z targets (Be and C). Here, the ratios obtained by using the ITS 3.0 code are closer to unity than those obtained by using the EGS5 code. The reason of this is the fact that the calculated value obtained by using the ITS 3.0 code is underestimated for low-Z targets; this underestimation can, in turn, be attributed to the use of the default value of the number of steps in the electron transport algorithm in the ITS 3.0 code.     

用Monte Carlo方法模拟γ射线散射M(?)ssbauer谱

本文将Monte Carlo方法应用于γ射线散射式Mossbauer谱的模拟,提出了平面模型,用统计估算法计算了不同厚度铁膜覆盖下的不锈钢样品的Mossbauer谱,并计算了两者子谱的面积比。通过一系列验证性实验,结果表明计算与实验是相符合的。这说明Monte Carlo方法可用来模拟γ射线散射Mossbauer谱。而且可以根据子谱面积比给出薄膜厚度的信息。     

Monte Carlo calculation of energy loss of hydrogen and helium ions transmitted under channelling conditions in silicon single crystal

In this work, we report on calculations of the electronic channelling energy loss of hydrogen and helium ions along Si〈1 0 0〉 and Si〈1 1 0〉 axial directions for the low energy range by using the Monte Carlo simulation code. Simulated and experimental data are compared for protons and He ions in the 〈1 0 0〉 and 〈1 1 0〉 axis of silicon. A reasonable agreement was found.Computer simulation was also employed to study the angular dependence of energy loss for 0.5, 0.8, 1, and 2 MeV channelled ⁴He ions transmitted through a silicon crystal of 3 μm thickness along the 〈1 0 0〉 axis.     

Monte Carlo calculations of low-energy electron dose-point-kernels in water using different stopping power approximations

The spatial distribution of absorbed energy in irradiated matter can be conveniently described by dose-point-kernel (DPK) distributions that characterize the average energy deposition around single charged-particle tracks during their slowing down process. In the present work, electron DPKs in liquid water in the energy range from 100 eV to 10 keV are presented based on Monte Carlo simulation of electron transport in the continuous-slowing-down-approximation (csda). Elastic collisions are individually simulated using the screened Rutherford formula, whereas the energy loss from inelastic interactions is determined from stopping power (SP) theory. Along with the standard Bethe SP formula we examine different empirical expressions of general-use which are meant to improve the performance of the Bethe formula at low electron energies. Comparison is also made with a recent Bethe-type parametric expression obtained from a dielectric optical data model of liquid water. Our findings indicate that for electron energies below ∼1 keV the discrepancies between the DPKs calculated by the general-purpose SP formulae become apparent. Moreover, the results obtained by the empirical expressions compare rather poorly with those from the dielectric model over the entire energy range examined.     

Monte Carlo Simulation of Gadolinium Neutron Gamma Spectroscopy Tracer Logging Method

The thermal neutron count and capture gamma ray spectroscopy before and after gadolinium seeping into sandstone and limestone formation are simulated by Monte Carlo Method, and the determination method of oil saturation is studied by using the thermal neutron count rate ratio and the n(Gd)/n(H) of capture gamma spectrum before and after gadolinium seeping. In addition, the relations of ratio with influence factors such as porosity, salinity of gadolinium seeping, saturation and lithology are given.      

Analytical and Monte Carlo computations of the energy losses by ionisation and their fluctuations in He

Computer programs have been developed to compute the energy loss by ionisation, its fluctuations, spatial distribution of the primary ionisation and cluster distribution, based on analytical and Monte Carlo methods. Results are presented for ⁴He in normal conditions of pressure and temperature and for ³He at P=4 atm and t=25C at intermediate energies, about 150 MeV, and minimum ionisation for pions, protons and deuterons.     

快电子能量损失谱仪的一种新的多道测量方法

介绍了一维位置灵敏探测器在高分辨快电子能量损失谱仪上的应用。系统地讨论了在定点测量模式和扫描测量模式下的针对此谱仪的数据处理方法,并提出了一种新的数据处理方法,可以在扫描模式下通过离线分析得到更细致的能谱。     

Influence on electron energy loss spectroscopy of the niobium-substituted uranium atom: A density functional theory study

We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS forfand d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.     

用中子-伽玛能谱测定输油管内产液含油比例的Monte Carlo模拟

对输油管外采用中子—伽玛能谱测量以确定输油管内产液含油比例的方法进行了蒙特卡罗(Monte Carlo)模拟，模拟结果证明这种方法是成功的。     

GM计数管能量响应补偿的MC法模拟

针对GM计数管低能段过响应特性,探讨了一种用MC法对其进行能量响应补偿的方法。该方法在结合能量响应补偿理论与MCNP蒙特卡罗模拟方法的基础上,寻求利用理论方法先行计算出较为合适的补偿条件,继而应用MCNP有目的的进行模拟,减少模拟海选过程,提高实验效率。     

野外γ谱仪刻度的蒙特卡罗模拟

用蒙特卡罗方法对NaI(Tl)野外γ谱仪刻度进行模拟,计算谱仪的响应系数.通过与实验的比较,研究利用蒙特卡罗方法对NaI(Tl)野外γ谱仪进行刻度的可行性.结果表明,当模拟探测器对137Cs的能量分辨率从8%～14%变化时,模拟结果与实验结果的差别在12%以内.     

井型HPGe探测器探测效率的MC模拟

采用MC方法对井型HPGe探测器全能峰探测效率进行虚拟刻度。通过改变点源在井中的位置,研究了其探测效率变化规律,并进行了实验验证;同时模拟计算了探测器对0.1~1Me V能量的探测效率。模拟与实验结果表明:137Cs放射源在井中不同位置的实验测量结果与模拟值最大相对误差6.8%,最小相对误差1.5%;探测效率随放射源离井底距离增加而减小,随入射射线能量增大而减小。     

Comparison of Monte Carlo calculation methods for effective delayed neutron fraction

Monte Carlo calculation methods to estimate the effective delayed neutron fraction β_eff are investigated: one is proposed by Meulekamp et al. and the other is by Nauchi et al. It is revealed that both the methods calculate the delayed neutron fraction weighted with the importance functions defined by Kobayashi. The accuracy of the methods are also examined for several simple benchmark systems. Consequently, it is found that Meulekamp’s method causes ∼5% discrepancies in the β_eff values for fast systems; Nauchi’s method gives good results for fast bare systems but ∼10% discrepancies for fast reflected systems. Both the methods calculate the β_eff values approximately within the accuracy of ∼2% for thermal systems.     

Efficiency enhancements to Monte Carlo simulation of heavy ion elastic recoil detection analysis spectra

Monte Carlo (MC) simulation can be used to simulate heavy ion elastic recoil detection analysis spectra, including the broadening and tailing effects of multiple and plural scattering, although it is very costly in terms of computer time. In this work, kinematic relationships and experimental parameters are exploited to implement efficiency improvements in the MC modeling process. For thin films, incident ions that pass through the sample without undergoing a significant scattering event need not be tracked. Ions that might generate a detectable scattered or recoiled ion are predicted by generating, in advance, the impact parameters which will define its path. Light recoiled target atoms may be dealt with in the same way. For heavy atoms, however, the probability of large angle scattering events is so high that the paths of most recoil atoms are dominated by several scattering events with large angular deflections.     

高纯锗探测器全能峰效率的MC模拟

采用MC模拟高纯锗探头对轴向和边侧的点源全能峰效率,与实验测得的全能峰效率相比较发现二者存在较大的偏差。本工作通过不断调节晶体的半径、厚度和锗晶体外层铜支架厚度,获得了模拟计算的准确尺寸。结果表明:使用调整后的尺寸模拟计算的全能峰效率与实验效率在轴向方向的偏差在±5%以内,边侧方向在±6%以内,获得了较为准确的高纯锗探头物理模型。     

Monte Carlo模拟韧致辐射光子穿透闪烁体的能量和通量分布

在工业CT设计中,为了选择闪烁体的种类和几何尺寸,需要知道韧致辐射光子穿透闪烁体的能量和通量分布。根据Monte Carlo模拟光子输运过程的理论,模拟了2MeV、9MeV韧致辐射光子在NaI、CsI、CdWO4闪烁体内的输运过程,讨论了这类光子穿透闪烁体后光斑展宽问题和能量及通量的分布。研究表明,该方法可准确直观地定量分析韧致辐射光子在闪烁体内任意位置的能量和通量分布规律。     

钆示踪中子伽马能谱测井方法的蒙特卡罗模拟

利用蒙特卡罗方法分别模拟砂岩和石灰岩地层渗钆前后的热中子计数及俘获伽马能谱，研究利用渗钆前后的热中子计数率比R及俘获伽马能谱的计数比n(Gd)/n(H)确定饱和度的方法，确定R及n(Gd)/n(H)与孔隙度Φ、渗钆浓度、饱和度和岩性等影响因素的关系。