成都剂量体模(CDP)组织等效材料辐射等效性评价

在分析“成都剂量体模”（Chengdu Dosimetric Phantom,CDP）中常用辐射组织等效材料（肌肉脂肪组织混合等效材料、组织等效材料、躯干骨组织等效材料、脑组织等效材料和肺组织等效材料）的基本元素组成及其密度的基础上,对其质量衰减系数、有效原子序数、线性衰减系数和电子密度等参数进行测试和计算,并与人体的标准参数值进行比较。证明“成都剂量体模”的主要辐射组织等效材料能量响应范围宽,辐射等效性达到国际推荐标准A级,可作为检测标准广泛应用于各种放射诊断治疗设备和辐射防护仪器的标定。     

仿生皮肤等效材料超声波测试方法的研究

为评定汽车安全碰撞实验模拟人的皮肤肌肉等效复合材料的力学特性,提出仿生皮肤等效材料的超声检测方法。通过测试仿生皮肤等效材料对超声波声速、衰减、散射和吸收率的变化,建立仿生皮肤等效材料力学性质与超声回波信号频率之间的关系模型,对仿生皮肤等效材料的弹性模量、组织特性、粘弹性和松弛模量进行等效性的分析与评定。对3种不同密度的仿生皮肤等效材料的声速、弹性模量和声衰减等参数进行了测算,结果表明:该测试方法正确可行,测试数据为仿生皮肤等效材料的设计合成、制备提供力学参数依据,对仿生材料的力学等效性能评定有着重要的参考价值。     

带隙特性计算的等效梁元法与等效平面应变法

针对可简化为平面应变类力学问题的超材料，根据矩形薄板筒形弯曲理论，提出该类超材料带隙特性计算的等效梁元法。应用等效梁元法和常规等效平面应变法对负泊松比超材料的多种典型构型(内六角、星形、箭形和旋转三角形)的带隙特性进行数值计算，比较两种方法在带隙计算精度、计算效率及拓扑优化中适用性等方面的差异，并经试验测试结果进行验证。研究表明，等效梁元法和等效平面应变法的带隙计算精度均较高，与实测值误差在7%以内。等效梁元法在带隙计算效率上比等效平面应变法高约50%,但拓扑优化基结构模型的规模较大，适用于杆件类超材料结构拓扑优化。等效平面应变法带隙计算效率较低，拓扑优化基结构模型的规模较小，适用于连续体类及骨架类超材料结构的拓扑优化。该研究可为带隙超材料的拓扑优化设计提供参考。     

高能X射线下水等效材料对水的等效性研究

针对水等效材料校准医用加速器中存在的问题,通过对比法测量水体模和3种水等效材料校准医用加速器的剂量学差异,分别给出PTW 30013和IBA FC65-G两种类型探测器在校准深度为5 cm和10 cm的修正因子。针对加速器日稳定性校准的必要性,通过近7个月的日稳定性测量结果,给出加速器漂移量和引起漂移的可能原因;针对水等效材料在相对测量中对水的等效性,通过测量12个辐射野的输出因子,得出水等效材料在相对测量中与水一致。最后给出水等效材料在高能X射线下水吸收剂量校准时的建议和注意事项。     

修正的等效三层减反射膜及其制备

利用等效层和有效界面的概念,分析了修正的等效三层减反射膜系;对不同基底材料上的膜层最佳匹配进行了数字计算:介绍了作高折射率层的一些氧化物的性质及镀制工艺;给出了修正等效三层减反射膜的控制方法;讨论了间隔层薄膜材料非均匀性的影响,以及非均匀性的利用和改进;用MgF_2,zrO_2,Nd_2O_3等材料组成等效三层减反射膜,在5000埃～8000埃的波段范围内,单片平板玻璃(n=1.52)的平均透射率达99％;井已将该膜系应用于光学零件镀膜的批量生产中。     

钢筋混凝土梁的非线性均质材料本构等效

本文根据钢筋混凝土梁截面开裂、屈服、极限等三个受力状态,分别与等效材料截面三阶段等效,确定等效材料主要的力学参数,再根据梁整体力学性能对等效结果进行修正的方法,实现了钢筋混凝土梁与非线性均质材料本构关系的等效。针对屈服截面以后等效截面与混凝土截面的刚度差别较大的情况,提出折减钢筋或混凝土屈服应变的调整方法。根据本文提供的折减系数,两种材料的构件的非线性力学性能基本接近,达到了等效的目的。     

国家计量标准的国际等效性

国家计量标准的国际等效性为适应国家计量标准的国际等效性的要求，经过广泛的磋商和各国国家计量研究院的讨论，眼下一个有关建立关键比对网络的计划正在积极的酝酿当中。各国国家计量院都愈来愈迫切地面临着这样一个要求，即论证其国家标准与贸易伙伴国国家计量院的国家...     

电流变材料流变模型的等效参数化分析

针对电流变材料研究中常见的几种理论模型,通过能量等效的方式建立流变材料的等效材料参数,使材料模型便于应用于流变体连续复合结构分析.文中对各流变模型所体现的材料特性进行了对比,并研究了各模型在不同外激励频率和激励幅值作用下的等效材料参数变化.研究发现,对于电流变液这种特殊流变材料,在不同外加条件和特性阶段采用不同的材料模型进行模拟时,等效材料参数的变化规律有着明显差别,一方面,等效化过程可以将不同特性阶段内流变材料的复杂特性用较为简单的参数形式描述出来,另一方面,结合已有的阻尼结构分析方法,利用这些等效后的材料参数可以方便地将不同的流变材料模型运用到电流变复合结构的理论分析中.     

用FDTD方法研究颗粒型复合材料微波等效介电常数

本文提出了复合材料等效电磁参数的FDTD计算方法,介绍了FDTD方法计算吸波材料等效电磁参数的步骤.通过对立方体模型、球形模型、连续模型和十字叉模型的仿真计算,讨论了颗粒形状和接触情况对等效介电常数的影响.通过计算不同体积分数的材料模型的等效电磁参数,得到了颗粒型复合材料等效介电常数的计算公式.通过实测复合材料的介电常数,证明了本文提出的公式是有效的.     

基于全场等效损伤测试的累积损伤模型

在固定的一组循环数下，对其中每一预定循环数进行不同应力水平的疲劳试验，并测出材料的韧性变化率，以此为损伤变量得到该组循环数下损伤量与交变应力水平关系的曲线族。该曲线族可以转换成相同损伤量下交变应力与循环数关系的等效损伤线族，通过对三种材料等效损伤线族测试和分析，给出损伤线族方程表达式，由此得到的累积损伤模型可以计算复杂加载下材料的剩余寿命，多级加载实验结果与测试值较好符合。     

用HXCF测量物质X射线质量衰减系数

X射线质量衰减系数是研究X射线的一个重要物理量,硬X射线探测器地面标定装置由于其单色性、稳定性以及其可测的绝对光子数,成为了研究质量衰减系数的一套理想装置.使用Cu、A12种不同材料分别在X射线能量为30 keV、50 keV、80 keV、100 keV和110 keV的情况下对其质量衰减系数进行测量,并将测量值与NIST的参考值进行了对比,得到了其标准偏差.根据NIST提供的质量衰减系数曲线,验证了Cu和Al在110keV处的质量衰减系数,为进一步研究做好了基础.     

Verification of some building materials as gamma-ray shields

The shielding properties for gamma rays of a few low Z materials were investigated. The values of the mass attenuation coefficient, equivalent atomic number, effective atomic number, exposure buildup factor and energy absorption buildup factor were calculated and used to estimate the shielding effectiveness of the samples under investigation. It has been observed that the shielding effectiveness of a sample is directly related to its effective atomic number. The shielding character of any sample is a function of the incident photon energy. Good shielding behaviour has been verified in soil samples in the photon energy region of 0.015-0.30 MeV and of dolomite in 3-15 MeV. The results have been shown graphically with more useful conclusions.     

Calculation of radiation attenuation coefficients, effective atomic numbers and electron densities for some building materials

Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (μ/ρ), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (σ(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory.     

A Monte Carlo investigation of electron backscattering

Kearsley's, Haider's and Frujinoiu's cavity expressions depend upon the existence of reliable data on electron backscattering in different media. These data are not available in the literature. By using MCNP, backscatter distributions and their saturation values were obtained for electron beams with energies between 0.1 MeV and 9 MeV traversing different materials such as polyethylene, solid water, lithium fluoride, aluminium, copper and lead. The data obtained using MCNP show that electron backscatter probability most strongly depends on the scatterer's effective atomic number and electron energy. Backscatter probability becomes less dependent on energy and is mostly a function of the effective atomic number of the scatterer for electron energies below 0.5 MeV. For low atomic number materials MCNP data suggest that the backscatter saturation values are distributed linearly with the effective atomic number of the scatterer for all energies investigated.     

Monte Carlo simulation for energy deposition of an ionisation chamber based on the equivalent electron source theory and experimental verification for the theory

The main research described in this paper includes three sections. First, research on the response of the stainless steel ball-shaped ionisation chamber by experimental methods. Secondly, calculation of the response of the chamber with the general Monte Carlo EGS4 code in order to compare with the equivalent electron source theory by calculation methods. Finally, calculation of the response of the ionisation chamber with the equivalent electron source theory. The results show that the calculated results of the equivalent electron source theory coincide very well with those of the experiments when the atomic number of the chamber wall is close to one of the gases (such as Ar and Kr), and the calculated results coincide with those of the experiments to a certain extent when the atomic number of the chamber wall is not close to one of the gases (such as He and Xe).     

Atomic‐Scale Structure Evolution in a Quasi‐Equilibrated Electrochemical Process of Electrode Materials for Rechargeable Batteries

Lithium‐ion batteries have proven to be extremely attractive candidates for applications in portable electronics, electric vehicles, and smart grid in terms of energy density, power density, and service life. Further performance optimization to satisfy ever‐increasing demands on energy storage of such applications is highly desired. In most of cases, the kinetics and stability of electrode materials are strongly correlated to the transport and storage behaviors of lithium ions in the lattice of the host. Therefore, information about structural evolution of electrode materials at an atomic scale is always helpful to explain the electrochemical performances of batteries at a macroscale. The annular‐bright‐field (ABF) imaging in aberration‐corrected scanning transmission electron microscopy (STEM) allows simultaneous imaging of light and heavy elements, providing an unprecedented opportunity to probe the nearly equilibrated local structure of electrode materials after electrochemical cycling at atomic resolution. Recent progress toward unraveling the atomic‐scale structure of selected electrode materials with different charge and/or discharge state to extend the current understanding of electrochemical reaction mechanism with the ABF and high angle annular dark field STEM imaging is presented here. Future research on the relationship between atomic‐level structure evolution and microscopic reaction mechanisms of electrode materials for rechargeable batteries is envisaged.     

Heavy metallic oxide nanoparticles for enhanced sensitivity in semiconducting polymer x-ray detectors

Semiconducting polymers have previously been used as the transduction material in x-ray dosimeters, but these devices have a rather low detection sensitivity because of the low x-ray attenuation efficiency of the organic active layer. Here, we demonstrate a way to overcome this limitation through the introduction of high density nanoparticles having a high atomic number (Z) to increase the x-ray attenuation. Specifically, bismuth oxide (Bi(2)O(3)) nanoparticles (Z?=?83 for Bi) are added to a poly(triarylamine) (PTAA) semiconducting polymer in the active layer of an x-ray detector. Scanning electron microscopy (SEM) reveals that the Bi(2)O(3) nanoparticles are reasonably distributed in the PTAA active layer. The reverse bias dc current-voltage characteristics for PTAA-Bi(2)O(3) diodes (with indium tin oxide (ITO) and Al contacts) have similar leakage currents to ITO/PTAA/Al diodes. Upon irradiation with 17.5?keV x-ray beams, a PTAA device containing 60?wt% Bi(2)O(3) nanoparticles demonstrates a sensitivity increase of approximately 2.5 times compared to the plain PTAA sensor. These results indicate that the addition of high-Z nanoparticles improves the performance of the dosimeters by increasing the x-ray stopping power of the active volume of the diode. Because the Bi(2)O(3) has a high density, it can be used very efficiently, achieving a high weight fraction with a low volume fraction of nanoparticles. The mechanical flexibility of the polymer is not sacrificed when the inorganic nanoparticles are incorporated.     

A Simulator for Producing of High Flux Atomic Oxygen Beam by Using ECR Plasma Source

In order to study the atomic oxygen corrosion of spacecraft materials in low earth orbit environment, an atomic oxygen simulator was established. In the simulator, a 2.45 GHz microwave source with maximum power of 600 W was launched into the circular cavity to generate ECR (electron cyclotron resonance) plasma. The oxygen ion beam moved onto a negatively biased Mo plate under the condition of symmetry magnetic mirror field confine, then was neutralized and reflected to form oxygen atom beam. The properties of plasma density, electron temperature, plasma space potential and ion incident energy were characterized. The atomic oxygen beam flux was calibrated by measuring the mass loss rate of Kapton during the atomic oxygen exposure. The test results show that the atomic oxygen beam with flux of 1016-1017 atoms-cm-2·s-1 and energy of 5-30 eV and a cross section of φ80 mm could be obtained under the operating pressure of 10-1-10-3 Pa. Such a high flux source can provide accelerated simulation tests of mater