组织辐射等效材料等效性验证方法的探讨

组织等效材料是设计、制造和应用仿真辐照人体模型的技术关键，要做到X-射线在辐照体模内与活体散射、吸收和分布的相似性以满足材料的组织等效性的要求，因此对组织等效材料的宏观、中观、微观三个层次上表征就显得极其重要。根据“参考人”的各组织器官密度和元素组成可以算出人体各种组织有效原子序数，电子密度和质量衰减系数等，用于判断和检验组织等效材料的辐射等效性。     

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。     

球冠型入射光学系统中等效辐射平面位置的计算

为了满足包括太阳直射和天空散射在内的2π球面度立体角范围的入射光线的测量需求，要求太阳紫外光谱辐射测量装置的入射光学系统必须具备较好的余弦响应特性。研制的入射光学系统由聚四氟乙烯积分球、磨砂石英球冠型余弦漫射器和修正环组成，积分余弦误差〈f2〉=0．94％。引入等效辐射平面接收器的概念，根据漫射器的几何形状和上面的光谱辐射照度分布以及接收系统的角度响应特性，采用数学分析方法对漫射器和积分球组合入射光学系统的等效辐射平面位置进行了精确计算，分析了影响等效辐射平面位置的因素，并采用实验统计方法进行了验证。     

基于等效辐射声功率和形貌优化的车身结构噪声控制

以某车型白车身为研究对象，首先建立白车身结构有限元模型并验证其有效性；随后通过对模型进行等效辐射声功率分析，得到白车身关键板件对车内的辐射噪声水平，并识别贡献量较大的结构位置；再根据分析结果构建白车身形貌优化模型并进行计算求解；最后将优化前后白车身等效辐射声功率进行对比，优化后辐射噪声在分析频段内整体降低，且最大响应峰值降低3.8 d B。研究结果表明，在汽车白车身设计阶段，基于等效辐射声功率分析和形貌优化设计可以有效地抑制结构的辐射噪声。该方法和思路可为工程领域相关的结构噪声分析和控制提供参考。     

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。     

用于QCT的新型脊椎骨矿密度体模的研制

为改进QCT在检测脊椎骨矿密度中与体模标准样品的比较精度,研制新型的QCT五标样体模。采用聚乙烯塑料同适量的碳酸钙及氧化镁混合,并用数控塑料造粒机加工成软组织的辐射等效颗粒材料(称软组织材料)。接着用颗粒材料同适量的羟磷酸钙混合,然后用数控塑料注射机加工成骨组织的辐射等效材料(称骨材料)。将骨材料机械加工成含5种羟磷酸钙密度的骨标准样品(称骨标样),将骨标准样品嵌入软组织材料块中,加工成五标样新型体模。通过对CP体模进行性能测试,并与国内外体模作对比,结果表明:新型体模的5个骨标样的羟磷酸钙密度分别为0,50,100,150,200 mg/cm~3,各骨标样的羟磷酸钙密度与相应的CT数呈线性相关,其相关系数r≥0.999 96,用于QCT检测脊椎骨矿密度测量有利于提高线性拟合精度。     

美国仿制药生物等效性研究简介

生物等效性评价不仅仅用于仿制药批准的过程中,同时在新药的开发、新药生产工艺和剂型的变换过程中,也发挥着非常重要的作用’。在美国,任何仿制药品上市,都必须经由美国食品药品监督管理局（FDA）批准。仿制药生产厂家须出示数据证明受试药品（仿制药品）与参比药品（原研药品）具有药学和生物等效性。生物等效性是指在相同的试验条件下,给予相同剂量的两种药学等效制剂,其活性成分吸收程度和速度无显著差异。     

关于JJG 1078-2012规程中的几个问题讨论

该文对JJG 1078-2012《医用数字摄影(CR、DR)系统X射线辐射源》规程中的计算图像均匀性方法和低对比度分辨力模体及衰减模体的等效材料问题进行讨论,得出两个结论:(1)图像均匀性计算方法采用图像处理软件测量需拟合出灰度-剂量曲线,方能作为判断图像均匀性的结果,(2)低对比度分辨力模体及衰减模体如采用铜等效材料,需要考虑的因素很多(比如厚度值很难确定,低对比度值范围很小),不能作为提供质控或计量检测的标准模体。     

蜂窝芯体面外方向导热系数等效研究

利用商用有限元软件分析了高温阶段蜂窝芯体面外方向等效导热系数,分析结果与试验数据和半经验公式结果进行了对比,对比结果显示有限元软件可以用来预测蜂窝芯体面外方向等效导热系数。利用有限元软件分析了低温阶段蜂窝芯体面外方向等效导热系数,证明在0℃以下时辐射换热对蜂窝芯体面外方向导热系数的影响可以忽略,同时得到了铝合金蜂窝芯体在0℃以下时面外方向等效导热系数近似公式。     

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.     

A new mammography dosimetric phantom

Breast phantoms produced with tissue-equivalent materials are used in an attempt to simulate glandular and adipose tissues, in terms of X-ray attenuation and density. In this work, a set of breast tissue-equivalent phantoms (BTE phantoms) with semicircular shapes of different thicknesses and compositions were produced. Such phantoms may be used in the measurement of the incident air kerma (K(i)) and the mean glandular dose (D(G)) delivered to patients undergoing mammography. To characterise the materials used to produce the phantoms, a series of 17-keV X-ray attenuation coefficient measurements were performed. The carbon-nitrogen-hydrogen elemental composition and the densities of the tissue-equivalent materials were also determined and compared with values available in the literature. Linear attenuation coefficients of 0.724 and 0.923 cm(-1) were determined, respectively, for adipose and glandular tissues. Such values agree with data available in the literature. On the basis of the results obtained in this work, it is suggested that BTE phantoms are used instead of polymethyl methacrylate phantoms to select exposure parameters (kV, mAs and target/filter combination) specific for breast glandularities from 0 to 50 % in the optimisation of doses in mammography.     

Modeling of radiation hardening in ferritic/martensitic steel using multi-scale approach

Fe-Cr based ferritic/martensitic (FM) steels are the candidate structural materials for future fusion reactors. In this work, a multi-scale approach comprising atomistic and dislocation dynamic simulations are used to understand the hardening of these materials due to irradiation. At the atomic scale, molecular dynamics (MD) simulations are used to study the mobility of an edge dislocation and its interaction with irradiation induced voids and bubbles. The dislocation dynamics (DD) simulations are used to estimate the change in flow stress of the material as a result of irradiation hardening. The key input to the DD simulations are the friction stress and maximum shear stress for the edge dislocation to overcome the defects as determined from atomistic simulations. The results obtained from the MD and DD simulations are in qualitative agreement with experimental results of hardening behavior of irradiated FM steels.     

A promising new class of irradiation tolerant materials: Ti2ZrHfV0.5Mo0.2 high-entropy alloy

Recently, high-entropy alloys (HEAs) or multi-principal-element alloys with unprecedented physical, chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their promising irradiation resistant behavior. Here, we report a new single-phase body-centered cubic (BCC) structured Ti₂ZrHfV_0.5Mo_0.2 HEA possessing excellent irradiation resistance, i.e., scarcely irradiation hardening and abnormal lattice constant reduction after helium-ion irradiation, which is completely different from conventional alloys. This is the first time to report the abnormal XRD phenomenon of metallic alloys and almost no hardening after irradiation. These excellent properties make it to be a potential candidate material used as core components in next-generation nuclear reactors. The particular irradiation tolerance derives from high density lattice vacancies/defects.     

Off-site toxic consequence assessment: a simplified modeling procedure and case study

The new "Hazardous Waste Management Regulation" was published in the Official Newspaper of the Chilean Republic on 12 June 2003, being in force 365 days after its publication (i.e., 12 June 2004). During the next 180 days after its publication (i.e., until 12 December 2004), each industrial facility was obligated to present a "Hazardous Waste Management Plan" if the facility generates more than 12 ton/year hazardous wastes or more than 12 kg/year acute toxic wastes. Based on the Chilean industrial figures and this new regulation, hazardous waste management plans were carried out in three facilities of the most important sectors of Chilean industrial activity: a paper production plant, a Zn and Pb mine and a sawmill and wood remanufacturing facility. Hazardous wastes were identified, classified and quantified in all facilities. Used oil and oil-contaminated materials were determined to be the most important hazardous wastes generated. Minimization measures were implemented and re-use and recycling options were analyzed. The use of used oil as alternative fuel in high energy demanding facilities (i.e., cement facilities) and the re-refining of the used oil were found to be the most suitable options. In the Zn and Pb mine facility, the most important measure was the beginning of the study for using spent oils as raw material for the production of the explosives used for metals recovery from the rock. In Chile, there are three facilities producing alternative fuels from used oil, while two plants are nowadays re-refining oil to recycle it as hydraulic fluid in industry. In this sense, a proper and sustainable management of the used oil appears to be promissory.     

Neutron shielding material based on colemanite and epoxy resin

In recent years, there has been a need for compact shielding design such as self-shielding of a PET cyclotron or upgradation of radiation machinery in existing facilities. In these cases, high performance shielding materials are needed. Concrete or polyethylene have been used for a neutron shield. However, for compact shielding, they fall short in terms of performance or durability. Therefore, a new type of neutron shielding material based on epoxy resin and colemanite has been developed. Slab attenuation experiments up to 40 cm for the new shielding material were carried out using a 252Cf neutron source. Measurement was carried out using a REM-counter, and compared with calculation. The results show that the shielding performance is better than concrete and polyethylene mixed with 10 wt% boron oxide. From the result, we confirmed that the performance of the new material is suitable for practical use.     

Dose inhomogeneities for photons and neutrons near interfaces

Perturbations of charged particle equilibrium (CPE) at interfaces of materials of different atomic composition can lead to considerable differences in the energy deposition by photons and neutrons. Specific examples of these interface perturbations are encountered during irradiation of body cavities and soft tissue adjacent to bone or metallic implants and irradiation of cells in monolayer on the bottom of culture dishes. Another example is the build-up of CPE at air-tissue interfaces, referred to in radiotherapy as the skin sparing effect. For photon irradiation excess production of secondary electrons in high-Z materials, such as glass, bone or gold, will induce appreciably higher doses and decreased cell survival compared to the equilibrium situation. The energy dissipation of fast neutrons in biological materials occurs through recoil protons, heavy recoil nuclei and products of nuclear reactions. Owing to the large contribution from recoil protons to the neutron kerma, the hydrogen content of the biological material mainly determines the energy deposition. For neutron irradiation of cells in monolayer, CPE can be established or deliberately avoided by mounting tissue-equivalent plastic or carbon discs in front of the cells, respectively. This approach makes it possible to distinguish the biological effects of the low- and high-LET radiation components.     

Fast-neutron OSL sensitivity of thallium-doped ammonium salts

The main problem in selecting suitable thermoluminescent (TL) materials for fast-neutron dosimetry is finding a material that is both tissue-equivalent and not damaged upon heating. Optically stimulated luminescence (OSL) avoids the need to heat the materials and allows the use of materials with a high content of hydrogen (responsible for 90% of the absorbed dose of fast-neutrons). The choice of studying the ammonium salts for their OSL properties was based on the calculation of their neutron kerma factor. A constant ratio of an ammonium salt's kerma coefficients to the tissue's kerma coefficients (in the fast-neutron range) is a prerequisite for a similar energy response to neutrons, i.e. tissue equivalency. The salts studied are NH4Br and (NH4)2SiF6 both doped with Tl+. This paper describes the OSL properties of Tl(+)-doped NH4Br and (NH4)2SiF6 after exposure to 14.5 MeV neutrons to explore their potential for developing new, tissue-equivalent OSL materials suitable for fast-neutron dosimetry. The relative neutron sensitivity, k, defined as the ratio of the sensitivity of the material to neutrons to its sensitivity to gamma rays, has been determined for 14.5 MeV neutrons and varies between k = 0.15 and k = 0.5. The latter value is a factor 2.5 higher than that found for known TL materials (k < or = 0.2). A drawback of these materials is the fast fading of the OSL signal.     

聚合物的水声声衰减能力与动态力学性能的关系

以描述高分子材料粘弹行为的三元模型为出发点,以声波在高分子介质中的传播理论为依据,推导出了材料的水声声衰减能力与材料的动态力学性能参数包括损耗因子、松弛前的剪切模量、松弛后的剪切模量以及材料的密度和厚度之间的关系式。为实验验证所推导的关系式,设计合成了一系列阻尼性能不同的聚合物,分别测试了它们的动态力学性能和声衰减能力。用材料的动态力学性能参数计算得到的水声声衰减系数与实验测得的声衰减能力相符合。该数学模型为找出吸声系数与材料的动态力学性能之间的关系、指导水声材料设计奠定了基础。