共查询到19条相似文献,搜索用时 171 毫秒
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利用蒙特卡罗方法模拟了锥束工业CT系统中X射线的产生过程,分别得到了未加过滤层和加2mm铁片作为过滤层情况下的X射线能谱;计算了不同靶面倾角下出射X射线相对强度的角分布。随后模拟了X射线通过被测物体后射线强度的分布,分别得到了射线源与探测器间距离相同时,穿过不同直径被测物体以及经过相同的被测物体,但射线源与探测器间距离不同的两种情况下的系统SPR值的分布以及探测器平面不同位置下射线强度的分布。此外还模拟得到了有无被测物体情况下的探测器中心位置的通量能谱分布及一些特殊位置下射线强度的空间分布。模拟结果可以为CT系统图像重建时的散射校正和射束硬化校正提供数据依据,有助于确定探测器单元的最小灵敏度以及为系统的屏蔽防护设计提供参考。 相似文献
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《特种铸造及有色合金》2017,(4)
利用小角X射线散射(SAXS)技术研究了Cu-0.6Fe合金在500℃时效过程中的析出相。结果表明,Cu-0.6Fe合金在500℃保温0~80min时,析出相的尺寸为4.5~5.9nm。通过透射电镜观测500℃×10min时效后试样组织,测得晶粒半径约为4.6nm,表明小角X射线散射法测量Cu-0.6Fe合金时效析出相尺寸是准确的,比透射电镜测量方法更具有统计意义和参考价值。 相似文献
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3层析射线成像
3.1基本原理
计算机辅助图像重建技术(射线层析照相技术,简称CT)不同于常规射线照相,是X射线从一系列角度入射物体,用数字方法重构物体内部结构断面图像的一种技术。为获得CT图像,要用探测器阵列检出被检物体的透射线(图15)。 相似文献
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利用高温高压反应釜,采用失重、电化学实验和慢应变拉伸方法,结合X射线衍射(XRD)、扫描电子显微镜(SEM)和能量散射X射线谱(EDS)等手段研究了0~3 MPa静水压力对X70钢在模拟海洋环境中的腐蚀行为的影响.结果表明:静水压力在0~2MPa范围内,X70钢的腐蚀形态表现为局部腐蚀,腐蚀产物主要成分为FeOOH.静... 相似文献
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射线数字成像检测技术 总被引:5,自引:4,他引:5
介绍多种射线数字成像(DR)系统的组成及成像机理,分析其性能指标、优缺点及应用领域。光子放大的DR系统(如图像增强器DR系统)实时性好,但适应的射线能量低,检测灵敏度相对较低;其它系统的检测灵敏度较高但成像时间较长。DR系统成像方式的主要区别在于射线探测器,除射线转换方式外,影响系统检测灵敏度的主要因素是散射噪声和量子噪声;可采用加准直器和光量子积分降噪的方法提高检测灵敏度。 相似文献
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第1专题射线衰减规律1.1射线衰减基本规律当X射线或γ射线射人物体时,其光量子将与物质发生复杂的相互作用,主要的相互作用是光电效应、康普顿效应、电子对效应和瑞利散射,主要相互作用与射线能量、物质原子序数的关系如图1─1所示。由于这些相互作用,使从物体透射的射线强度低于入射射线强度,这称为射线强度发生了衰减。在上述四种相互作用中,入射光量子的能量一部分转移到能量或方向改变了的光量子那里,一部分转移到与之相互作用的电子或产生的电子那里。电子将继续与原子发生相互作用,转移到电子的能量主要损失在物体之中。前… 相似文献
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采用物理气相沉积(PVD)磁控溅射沉积方法,通过改变轰击离子能量制备高密度的V2AlC涂层,并探究不同轰击离子能量对涂层结构和性能的影响。利用能谱仪测试、X射线衍射、拉曼光谱、扫描电镜、原子力显微镜对涂层的化学组成、相结构、表面与截面形貌进行分析,同时利用纳米压痕测试评价V2AlC涂层力学性能。结果表明,提高轰击离子能量从15 eV到35 eV可以有效使得V2AlC涂层致密化,且降低涂层表面粗糙度~50%(从~20.2 nm到~11.9 nm),同时提高涂层的硬度~50%(从~14 GPa到~21 GPa),与杨氏模量~20%(从~309 GPa到~363 GPa)。但当轰击离子能量升高到50 eV时,Al元素含量急剧下降,涂层由V2AlC相转变为V2C与VC多相混合。轰击离子能量的提高有效改善V2AlC涂层的结构,提高V2AlC涂层的硬度,杨氏模量,但需控制轰击离子能量改变范围才可实现结构与性能最优化。 相似文献
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A new type of pyrometer is developed, in which two optical fibers are used to accept and transmit the infrared energy. These two fibers are connected using a non-contact fiber coupler. In turning, the incidence face of one optical fiber which is embedded in a rotating workpiece accepts the infrared rays radiated from the cutting tool and emits it at the other face. The infrared energy is accepted by the other optical fiber which is fixed at the pyrometer and led to the two-color detector. In endmilling, the temperature history of CBN tool face during cutting is measured, where the fiber is embedded in the endmill. 相似文献
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Laser Powder Bed Fusion is a leading additive manufacturing technology, whose use has been recently extended to refractory metals such as tungsten. This work was carried out to manufacture a pure tungsten pinhole collimator that would otherwise be difficult to produce using conventional methods such as machining. The laser powder bed fusion process was used to produce an ultra-fine 0.5 mm diameter hole running along a 40 mm long beam stop component. A laser powder bed fusion scanning strategy (laser energy density of 348 J/mm3) was selected with the aim of fabricating a high density tungsten component. The manufactured collimator was then used for gamma-ray detector characterisation. A collimated gamma-ray using a 241Am source mounted on an automated scanning table was used to study the gamma-ray interaction with respect to position in a semiconductor detector, so that the position-dependent charge collection process could be characterized. The 0.5 mm diameter fine tungsten collimator yielded a relatively narrower beam spot, leading to more accurate scan results. However that was at the expense of number of gamma rays detected per second. Overall, the 0.5 mm collimator allowed for higher resolution scans giving better detector characterisation results in comparison to a 1 mm diameter collimator. 相似文献
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CREEPPROPERTIESOFHIGHSILICONALLOYZA27PREPAREDBYSPRAYDEPOSITION¥YANGLiushuan;LIUYongchang;YANGGencang;ZHOUYaohe(StateKeyLabora... 相似文献
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采用场发射扫描电镜(FESEM)、X射线光电子谱(XPS)、高角环形暗场扫描透射电镜(HAADF-STEM)以及程序升温脱附与质谱联用(TPD-MS)等表征手段研究了不同窄粒度范围镍基高温合金粉末的原始表面状态以及存储和脱气等增/降氧过程对合金组织和性能的影响。结果表明:不同粒度原始态粉末的表面组成均为Ni O/Ni(OH)2、TiO2、CoO和Cr2O3,0~15μm粒径粉末(细粉)和150~180μm粒径粉末(粗粉)平均氧化膜厚度分别为3.32和10.90 nm。细粉和粗粉在空气环境中存储后氧含量逐渐增大,在3~10 d达到稳定值,分别约为250×10-6和40×10-6。存储后0~53μm粉末制备的块体合金氧含量升高,室温、650℃和750℃拉伸强度变化不大,但塑性下降,合金在650℃、890 MPa和750℃、530 MPa的持久性能均下降。0~15μm细粉加热过程中(室温~1000℃)会发生气体脱附,存在明显脱附峰的气体包括CO2 相似文献
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NiCrAlY bond-coat was coated on Inconel 718 substrate by air plasma spraying (APS) followed by APS ZrO2-8 wt.%Y2O3 as top-coat. Using CO2 laser of different energy densities, ceramic top-coat surface was remelted. Laser remelting with high energy density (4 J/mm2) produced a dense microstructure over the whole thickness of top-coat, while low energy density (0.67 J/mm2) laser remelting produced a ~ 50 μm thick dense layer on the top-coat surface. It was found that the volume fraction of monoclinic phase decreased from 9% in as-sprayed coating to 4% and 3% after laser remelting with high and low energy density respectively. After isothermal oxidation at 1200 °C for 200 h, the thickness of oxide layer (TGO) in the sample produced by low energy density laser remelting was ~ 5.6 μm, which was thinner than that of oxide layer in as-sprayed (~ 7.6 μm) and high energy density laser remelted (~ 7.5 μm) samples. A uniform and continuous oxide layer was found to develop on the bond-coat surface after low energy density laser remelting. Thicker oxide layer containing Cr2O3, NiO and spinel oxides was observed in both as-sprayed and high energy density laser remelted coatings. After cyclic oxidation at 1200 °C for 240 h, the weight gain per unit area of as-sprayed coating was similar to that of high energy density laser remelted coating while a significantly smaller weight gain was found in low energy density laser remelted coating. 相似文献
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中海石油(中国)有限公司天津分公司为了节能减排,在渤海湾某油田开展了天然气利用项目,天然气外输海管选用X65管线钢铺设完成。随着油田不断深入开发,天然气中CO2和H2S含量都达到了较高水平,使该海底管线在运行过程中面临潜在的不确定性腐蚀风险。因此,本文研究了在不同运行工况条件下的X65钢海管焊缝区及热影响区的腐蚀形态和腐蚀规律。试验结果表明,在管线钢的焊缝区和热影响区存在不同程度的均匀腐蚀,而点蚀相对比较轻微;试样整体均匀腐蚀速率达0.1~0.3mm/a,属于中等偏高的腐蚀程度;pH降低、温度升高会使腐蚀速率增大,在管线运行和维护过程中需针对均匀腐蚀采取控制措施。本研究可以为今后海底管线选材、焊接工艺以及后期运维等工作提供借鉴。 相似文献
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Recently, one of us (O.L.M.) developed a theoretical approach to the energy transfer process between a ligand and a lanthanide ion in luminescent compounds. This approach takes into account the direct Coulomb interaction only. Here we present further calculations which also include the exchange Coulomb interaction (isotropic and anisotropic). The selection rules on the total angular momentum, J, of the lanthanide 4f states, derived from each interaction are different. They are in fact complementary. We discuss the case of energy transfer to the 5D1 manifold of the Eu3+ ion, which is forbidden when only the direct Coulomb interaction is considered but becomes allowed through the exchange interaction. In this case numerical estimates show that, depending on resonance conditions and the nature of the ligand donor state, the transfer rate may assume very high values. It is also emphasised that, according to the present approach, energy transfer to the 5D0 level of the Eu3+ ion is forbidden by both mechanisms, provided J-mixing between the 7F0 and 7F2 manifolds is neglected. 相似文献