基于RMC程序的用康普顿轮廓进行束缚态电子多普勒展宽修正研究

堆用蒙特卡罗程序RMC具备中子、光子、电子耦合输运能力，能完成精确的屏蔽计算，其中光子输运过程采用光子数据库进行了康普顿散射模拟。本文对康普顿散射物理原理及多普勒展宽方法进行分析，使用康普顿轮廓数据对束缚态电子进行多普勒展宽修正，实现了RMC程序对自由电子和束缚态电子的选择性处理。通过核素算例测试，观察到了多普勒能谱展宽的效应，证明了该方法的正确性。通过对典型压水堆组件的计算和对比，验证了用康普顿轮廓进行束缚态电子多普勒展宽修正的必要性和正确性。     

光子在组织等效介质中产生的次级电子能量分布研究

本文探讨了不同能量光子在组织等效物质中产生的次级电子在能量上的分布规律.依据理论分析和计算,明确了水作为组织等效材料的合理性,利用MC方法中粒子输运技术,对光子在介质中行为进行了真实模拟.通过大量模拟计算,得到了不同能量光子与介质中原子(H、O)相互作用的事件类型的比例分布情况以及在这些事件中产生的次级电子能量分布的真实情形.光子能量小于28keV时,光子与介质原子之间的作用以光电效应为主;能量为28～30keV的光子,光电效应与康普顿散射几率大致相等;能量大于30keV的光子,康普顿散射事件逐步占据主导地位,这种事件几率随光子能量的增加而增大.     

利用γ-γ土壤密度探头测量沙卵石地层的密度

利用γ-γ土壤密度探头测量沙卵石地层密度的主要困难是不能用压打和震动的方法下进路管,为此不得不用地质勘探钢管钻孔进行测量。然而地质钻孔孔径较大,用γ-γ土壤密度探头测量时,井内散射本底远大于来自地层的康普顿散射光子,不能分辨地层密度。我们采用了图1的探头系统,用垂向屏蔽体屏蔽来自井内的康普顿散射光子,使探测器只记录来自地层的散射光子,对沙卵石地层密度进行测量。所用放射源为~(137)Cs,210mCi,源到探测器中心的距离为36cm。探头系统的提放利用了细钢丝绳、三角架和小型绞车。利     

EGS程序光子输运模型研究进展

随着EGS在辐射物理和医学物理等众多方面的广泛应用,其物理内核被EGS开发小组所不断更新,光子的输运模型也越来越完善.本文综述了光子输运模型的进展,包括线性极化光子散射、康普顿散射中的电子约束等效应以及光子截面数据库的更新.     

基于高能X射线散射的高原子序数物质探测方法

针对核材料的探测问题,利用其高原子序数（Z）的特性,提出了基于散射能谱解析识别物质原子序数的方法。该方法通过对X射线与物质相互作用所产生的散射光子的测量和分析来进行物质识别,这些光子包括正电子湮没光子、轫致辐射光子和康普顿散射光子,携带了物质原子序数的信息。蒙特卡罗模拟计算结果表明,该方法能够分析核素的原子序数,尤其对核材料等高Z物质的分析更为有效。采用LaBr₃(Ce)探测器测量了基于7MeV电子直线加速器的多个样品的散射能谱,结果表明,该方法能有效区分高原子序数物质。     

6MeV探伤加速器屏蔽体设计

正探伤用电子直线加速器主要产生电离辐射,其中对X射线的防护是重点。根据射线不同,屏蔽材料的选择有所区别。对于X射线,已知高能光子流与物质作用主要产生光电效应、康普顿散射和游离电子对等3种效应。光电效应产生概率与屏蔽材料原子序数4次方呈反比;康普顿散射     

电子对效应对D-T次生γ密度测量的影响

为研究电子对效应对D-T可控中子源地层密度测量精度的影响,本文首先分析传统的化学源密度测井原理,其次研究中子次生γ射线发生电子对效应与康普顿散射的质量衰减系数差异,并使用蒙特卡罗模拟方法研究传统密度测井和中子次生源密度测量精度,计算其误差大小、分析误差来源和提出校正方法。结果表明,密度测井主要利用γ射线的康普顿散射,当使用中子次生的高能γ射线测量地层密度时,其精度比化学源方法低,这种误差主要是由于高能γ射线的电子对效应引起,最大可以达到传统方法的2.7倍;电子对效应对于地层岩性比较敏感,如果对衰减的γ信号进行岩性校正,则可以提高密度测量的精度。     

核技术在骨质密度测量方面的应用

本文概要介绍应用核技术的几种测量骨质密度方法:单光子吸收测量、双光子吸收测量、双能X射线吸收测量、双光子γ照相、计算机化断层图像黑度定量(QCT)、双能X射线QCT、γ射线QCT、康普顿散射测量、光子相干散射、活体中子活化延迟γ光子分析、活体中子活化瞬发光子分析等测量方法的近年进展。并对检测部位、受照剂量、准确度、精密度、正常人值、临床应用效果等方面进行了分析比较。     

能量从10 keV到300 MeV的电子和光子在物质中若干物理参数计算程序

本工作提供一组计算程序,可计算电子的能量损失(碰撞损失、轫致辐射损失、阻止本领)及射程、电子轫致辐射光子能谱及轫致辐射光子数目分布、电子和光子的反应几率(电子轫致辐射几率、电子同电子碰撞几率;光子康普顿散射几率、核场中对生成几率)。物质组成可分为单一元素、化合物或混合物。能量范围从10 keV到300 MeV分为75个间隔。以数据表的形式给出上述诸量。结果满意。     

低能X射线自由空气电离室散射和荧光光子修正因子的研究

为了减少散射和荧光光子在低能X射线自由空气电离室复现空气比释动能的影响,需要引入散射和荧光光子修正因子。运用EGSnrc MC模拟程序中的DOSXYZnrc程序包对6~50 ke V能量范围内X射线自由空气电离室的散射和荧光光子修正因子进行模拟计算,获得散射和荧光光子修正因子的值;参考CCRI的国际比对规范,对低能X射线规范下的5个辐射质的散射和荧光光子修正因子进行了模拟计算,得出散射和荧光光子修正因子的值。研究结果表明:所得散射和荧光光子修正因子不确定度为0.1%,可为低能X射线空气比释动能的国际比对提供数据支持。     

Chemical corrosion and gamma-ray attenuation properties of Zr and Ti containing lead silicate glasses

Lead silicate glasses (LSGs) have high gamma-ray attenuation but low chemical durability properties. In this work, LSGs with (55.5-68.5 wt%) PbO content containing ZrO₂ and TiO₂ additions were produced. The chemical corrosion of various produced LSGs in 0.5 N HNO₃ aqueous solution and determination of their gamma-ray attenuation coefficients for ⁶⁰Co and ¹³⁷Cs sources were investigated. The weight loss measurements, the SEM micrographs, the EDS analysis of the sample surfaces and the ICP analysis of solution were used to characterize the dissolution process. The effects of PbO content, ZrO₂ and TiO₂ additives on chemical corrosion, and also the effect of PbO on gamma-ray attenuation coefficient, glass transition temperature (Tg), and density of LSG glasses were determined. The results showed that by increasing the lead content of glass the gamma-ray attenuation coefficient, chemical corrosion and density were increased, but the Tg decreased. One of the samples with PbO contents of 65.4 wt% and SiO₂ content of 26.9 wt% showed a very low chemical corrosion behavior and good gamma-ray absorption property.     

Rayleigh to Compton ratio with monochromatic radiation from an X-ray tube (preliminary results)

Results on the Rayleigh to Compton ratio (R/C) for elements and compounds with low atomic number (5 ? Z ? 12) are presented. These materials are difficult to identify and characterize with other radiological techniques because of their very close linear attenuation coefficients. A transportable setup for R/C measurements was assembled and tested. This comprises an X-ray tube, in which the output radiation is partially “converted” to monochromatic radiation emitted by a secondary target. The experimental results are compared with theory, determined through coherent and incoherent scattering cross sections.     

Electronic structure of rhodium using Compton profiles: Experiment and theory

The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi ²⁴¹Am Compton spectrometer. To compare the experimental data, we have computed the Compton profiles and energy bands using spin-polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) and density functional theory schemes. The experimental and theoretical data are also compared with the available augmented plane wave and linear combination of Gaussian orbitals calculations. The origin of anisotropy in the momentum densities is discussed in terms of the energy bands and the Fermi surface topology. Among the various model calculations, it is seen that the KKR calculations are in better agreement with the absolute profiles but they significantly overestimate the anisotropy in momentum densities.     

Investigating the influence of gamma ray energies and steel fiber on attenuation properties of reactive powder concrete

The effect of gamma ray energies and volume ratio of micro steel fiber (1 and 1.5％) on attenuation properties of reactive powder concrete (70 MPa compressive strength) was investigated.Different characteristics have been considered such as linear attenuation coefficient,mass attenuation coefficient,and half-value thickness.Sodium iodide crystal with a gamma ray spectrometer and collimated beam of gamma ray has been implemented to perform the experimental test.Three sources (Cs-137,Co60,and Bi-207) with energies of (0.662,1.17 1.33,0.569,and 1.063)MeV were adopted in the test.The results obtained indicated that mass attenuation coefficient is proportioned inversely with gamma ray energies and directly with a volume ratio of micro steel fiber.The linear attenuation coefficient and half-value thickness of the tested samples have been calculated and discussed.The obtained results showed that increasing the volume ratio of steel fiber has modified the adequacy of the reactive powder concrete as a shielding element since it increases the density and reduces the half-value thickness.     

Analysis of Adsorption Behavior of Cesium onto Quartz Using Electrical Double Layer Model

The adsorption behavior of Cs onto quartz was investigated with the use of a high performance liquid chromatograph. The surface-based distribution coefficient (K_a) of Cs onto quartz was determined in the solution of which pH ranged from 6 to 11 and ionic strength from 10^?3 M to 10^?1 M. The K_a values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by an electrical double layer model and the optimum parameter values of the double layer electrostatics and adsorption reactions were obtained. The adsorption mechanisms of alkali metal ions was discussed on the basis of the present analysis.     

Rayleigh, Compton and K-shell radiative resonant Raman scattering in 83Bi for 88.034 keV γ-rays

The Rayleigh, Compton and K-shell radiative resonant Raman scattering cross-sections for the 88.034 keV γ-rays have been measured in the ₈₃Bi (K-shell binding energy = 90.526 keV) element. The measurements have been performed at 130° scattering angle using reflection-mode geometrical arrangement involving the ¹⁰⁹Cd radioisotope as photon source and an LEGe detector. Computer simulations were exercised to determine distributions of the incident and emission angles, which were further used in evaluation of the absorption corrections for the incident and emitted photons in the target. The measured cross-sections for the Rayleigh scattering are compared with the modified form-factors (MFs) corrected for the anomalous-scattering factors (ASFs) and the S-matrix calculations; and those for the Compton scattering are compared with the Klein-Nishina cross-sections corrected for the non-relativistic Hartree-Fock incoherent scattering function S(x, Z). The ratios of the measured KL₂, KL₃, KM and KN_2,3 radiative resonant Raman scattering cross-sections are found to be in general agreement with those of the corresponding measured fluorescence transition probabilities.     

Dielectronic recombination lines of C

The present paper presents atomic data generated to investigate the recombination lines of C ii in the spectra of planetary nebulae. These data include energies of bound and autoionizing states, oscillator strengths and radiative transition probabilities, autoionization probabilities, and recombination coefficients. The R-matrix method of electron scattering theory was used to describe the C²⁺ plus electron system.     

碳同素异形体的康普顿轮廓研究

本文介绍了用康普顿散射方法研究碳同素异形体的电子动量密度分布。实验中得到了碳不同结构材料的康普顿轮廓,发现由于晶体结构、成键方式的不同,它们的核外电子动量有着较显著的区别,纳米材料的表面效应表现明显。     

A method to measure the validity of trajectory simulation by removing the boundary-dependent coherent scattering contribution

A method is shown for measuring the validity of trajectory simulation, as compared to exact quantum calculation. The object is to calculate the differential cluster cross section obtained by multiple elastic scattering of a particle in a cluster of N randomly distributed point scatterers. After discussing the application of the analytic Foldy theory to the calculation of the coherent part of the cluster cross section, i.e. the diffraction pattern that is associated with the finite size of the cluster, it is shown that, for N up to ∼10³, this coherent part can be removed by a simple, exact procedure, allowing the trajectory simulation to be compared with the remaining incoherent part. A scalar measure of the relative error in the trajectory differential cluster cross section is introduced. In the examples shown, this relative error is negligible at a low density of scatterers, but increases substantially with increasing density. The relevance for low-energy electron scattering is discussed.     

Influence of screening length modification on the scattering cross section in LEIS

Scattering cross sections for He⁺ ions in the energy range of 100 eV to 100 keV and for Al, Cu and Au target atoms were calculated. Employing the Thomas-Fermi-Molière model the potential strength was tuned by variation of the screening length. The resulting change in scattering cross section was analyzed and the absolute value is compared to cross sections obtained from potentials commonly employed in the medium-energy ion scattering (MEIS) regime. A large influence on the scattering cross section is observed for targets with large atomic number in the very low energy range. For instance, the scattering cross section for 100 eV He⁺-ions scattered from Au by 129° changes by a factor of 2.5 between different potential strengths claimed in the literature to be suitable for low-energy ion scattering (LEIS) energies. An experiment to determine electronic energy loss of very slow ions in metals is presented. It shows how uncertainties in the scattering potential strength can lead to systematically wrong results, although perfect agreement between experimental data and simulations is found. The impact of these results on quantitative surface structure and composition analysis is discussed.