高能闪光照相中影响光程确定的几个因素

利用闪光照相基本原理和成像原理,在直接记录法和转换屏记录法的情况下,研究了闪光照相中影响X射线在材料中光程确定的主要因素。结果表明,影响光程确定的几个因素是：散射效应、光源角分布效应、立体角效应和能谱效应。对于高能闪光照相,散射效应是影响光程确定的最主要因素,散射的存在使光程的测量值比实际值降低20%～40%。因此必须在做CT之前,对散射的影响进行修正。     

闪光照相中X光能谱对有效吸收系数的影响

 研究闪光照相中影响材料有效吸收系数的两个主要因素，即X光的能谱效应和散射影响。用Monte-Carlo方法对闪光照相系统的客体各种组成材料的有效吸收系数进行数值模拟；求出不考虑散射而仅受能谱影响的有效吸收系数及其空间分布，发现该分布类似于医学CT数的分布规律，在高光程数对应的位置上该吸收系数较低；也得到了在20MeV闪光机情况下，客体各种组成材料的单个平均吸收系数。结果表明：钨、铝和铁的平均等效吸收系数分别近似为0.830，0.080和0.265cm ^-1。     

闪光照相中X光能谱对有效吸收系数的影响

研究闪光照相中影响材料有效吸收系数的两个主要因素,即X光的能谱效应和散射影响。用Monte-Carlo方法对闪光照相系统的客体各种组成材料的有效吸收系数进行数值模拟;求出不考虑散射而仅受能谱影响的有效吸收系数及其空间分布,发现该分布类似于医学CT数的分布规律,在高光程数对应的位置上该吸收系数较低;也得到了在20MeV闪光机情况下,客体各种组成材料的单个平均吸收系数。结果表明：钨、铝和铁的平均等效吸收系数分别近似为0.830,0.080和0.265cm-1。     

闪光照相系统的散射分布与降散射的数值模拟

对法国试验客体（FTO）的3 m照相系统建模,利用Monte-Carlo方法模拟X光子输运过程,得到了系统的散射分布和系统器件对散射的贡献。结果表明：后保护锥是系统散射的主要来源,对于任意一点,后保护锥的散射占总散射的75%以上。FTO的散射主要是FTO外层材料和边缘的散射,这部分散射占客体总散射的90%以上。利用坡度准直器对系统散射严重的区域进行的降散射,表明坡度准直器是一个很好的降散射器件,能有效提高图像质量。     

闪光照相系统的散射分布与降散射的数值模拟

 对法国试验客体（FTO）的3 m照相系统建模,利用Monte-Carlo方法模拟X光子输运过程,得到了系统的散射分布和系统器件对散射的贡献。结果表明：后保护锥是系统散射的主要来源,对于任意一点,后保护锥的散射占总散射的75%以上。FTO的散射主要是FTO外层材料和边缘的散射,这部分散射占客体总散射的90%以上。利用坡度准直器对系统散射严重的区域进行的降散射,表明坡度准直器是一个很好的降散射器件,能有效提高图像质量。     

闪光照相中散射分布均匀性的影响因素

为了在客体密度重建过程中采用迭代法扣除散射X射线的影响,提出了以散射分布均匀为主要目的的闪光照相系统设计思想。在介绍散射分布均匀性定义的基础上,分析了均匀扣除散射所带来的光程差。采用蒙特卡罗方法研究了系统放大倍数、照相距离以及后防护锥到图像接收系统的距离对散射分布均匀性的影响。结果表明：后防护锥到图像接收系统的距离是影响散射分布形状和散射照射量大小的一个主要因素;当后防护锥到图像接收系统的距离为55 cm左右时,散射分布均匀性近似最佳,而且照相距离越大,散射分布均匀性越好。这些研究结果可用于实际闪光照相系统的优化设计,在图像接收系统的响应范围内达到使散射分布均匀和降低光源模糊影响的目的。     

闪光照相中散射分布均匀性的影响因素

 为了在客体密度重建过程中采用迭代法扣除散射X射线的影响,提出了以散射分布均匀为主要目的的闪光照相系统设计思想。在介绍散射分布均匀性定义的基础上,分析了均匀扣除散射所带来的光程差。采用蒙特卡罗方法研究了系统放大倍数、照相距离以及后防护锥到图像接收系统的距离对散射分布均匀性的影响。结果表明：后防护锥到图像接收系统的距离是影响散射分布形状和散射照射量大小的一个主要因素;当后防护锥到图像接收系统的距离为55 cm左右时,散射分布均匀性近似最佳,而且照相距离越大,散射分布均匀性越好。这些研究结果可用于实际闪光照相系统的优化设计,在图像接收系统的响应范围内达到使散射分布均匀和降低光源模糊影响的目的。     

高能闪光照相中钨球散射规律研究

 用解析法和Monte Carlo法研究了钨球闪光X光照相的散射照射量空间分布随钨球半径、系统中元件构成以及保护器件与记录平面间距的变化规律。指出散射照射量的空间分布是不均匀的，它随球半径增加而变大；保护器件是散射照射量的主要来源，增加从保护器件到记录平面的距离，可以降低散射分布不均匀性，以及有效地减少散射。     

高能闪光照相中钨球散射规律研究

用解析法和Monte Carlo法研究了钨球闪光X光照相的散射照射量空间分布随钨球半径、系统中元件构成以及保护器件与记录平面间距的变化规律。指出散射照射量的空间分布是不均匀的,它随球半径增加而变大;保护器件是散射照射量的主要来源,增加从保护器件到记录平面的距离,可以降低散射分布不均匀性,以及有效地减少散射。     

高能闪光照相X射线能谱的理论研究

 用Monte-Carlo方法模拟球对称客体系统的闪光照相中X光光子的输运过程。分别在单客体情况和全系统情况下,给出了记录平面上各种光子谱及其在记录平面上的空间分布。结果表明：记录区边缘的谱形与源光子谱形很相似;深穿透区各点之间的谱形差别不大,谱平均光子能量近似相同,并且位于使高Z材料的光子线吸收系数最小的能量范围内。 结果还表明,高能闪光照相的光子能谱会因客体中光子的光程不同而有较大的差别。     

Study on the optical path difference of aero-optical window

To study the optical path difference (OPD) of optical widow in which light beams transmit under the aerodynamic thermal environment, a grid model is introduced. Based on it, the aero-optical effect of the side-mounted window is analyzed in detail combining the optical transmission theory and the numerical simulation method. Firstly, the temperature and stress of the window are simulated, and then the OPD is obtained through the refractive index. To demonstrate it, temperature field, deformation field and stress field of the window are calculated and analyzed. The influences of thermal shock and atmosphere pressure on the OPD are discussed.     

Factors affecting optical dispersion in borate glass systems

Series of ternary glass systems namely, Na₂O, B₂O₃, and RO (R=Ba or Mg) doped with TiO₂ are synthesized. The present glasses are dictated by requirement for a small refractive index and a small nonlinear coefficient needed for waveguide and laser fabrication requirements. The effect of MgO and BaO as alkaline earth metals on the optical properties of the glass systems is investigated. The dependence of the refractive index and extinction coefficient dispersion curves on composition is carried out over a wavelength range of 0.3-. Applying a genetic algorithm technique, the parameters of Sellmeier dispersion formula that fit index data to accuracy consistent well with the measurements are given. The zero material dispersion-wavelength (ZMDW) and group velocity are also determined using the refractive index data. The Fermi level is calculated exploiting the extinction coefficient dispersion curves. The absorption coefficient, both direct and indirect optical energy gaps, and Urbach energy are evaluated using the absorption edge calculations. The different factors that play a role for controlling the refractive indices such as coordination number, electronic polarizability, field strength of cations, bridging and nonbridging oxygen, and optical basicity are discussed in accordance with the obtained index data. IR spectroscopy is used as a structural probe of the nearest-neighbor environment in the glass network.     

Comparison study of photon attenuation characteristics of Lead-Boron Polyethylene by MCNP code,XCOM and experimental data

The linear attenuation coefficient, mass attenuation coefficient and mean free path of various Lead-Boron Polyethylene (PbBPE) samples which can be used as the photon shielding materials in marine reactor have been simulated using the Monte Carlo N-Particle (MCNP)-5 code. The MCNP simulation results are in good agreement with the XCOM values and the reported experimental data for source Cesium-137 and Cobalt-60. Thus, this method based on MCNP can be used to simulate the photon attenuation characteristics of various types of PbBPE materials.     

Analysis of the lateral displacement and optical path difference in wide-field-of-view polarization interference imaging spectrometer

The mechanism of beam splitting and principle of wide-field-of-view compensation of modified Savart polariscope in the wide-field-of-view polarization interference imaging spectrometer (WPIIS) are analyzed and discussed. Formulas for the lateral displacement and optical path difference (OPD) produced by the modified Savart polariscope are derived by ray-tracing method. The theoretical and practical guidance is thereby provided for the study, design, modulation, experiment and engineering of the polarization interference imaging spectrometers and other birefringent Fourier-transform spectrometers based on Savart polariscopes.     

Effect of dispersion of linear birefringence upon the sensitivity of an optical current sensor

The dispersion properties of the linear birefringence inside the glass current sensing head of a bulk glass optical current sensor and its effect upon the sensitivity of the sensor are theoretically analyzed and simulated with a computer. The investigation results show that the effect is small enough to be ignored, although it can certainly affect the scale factor of the system slightly. These results might be useful for the researchers and designers working in the optical current sensing techniques area.