A study of three-dimensional structures of interplanetary dust by imaging x-ray microtomography.

利用美国宇航局“星尘”任务收集的宇宙尘埃（行星际尘埃粒子和未熔化的微陨石）和彗星尘埃的三维结构，在“春-8”上进行了x射线显微断层扫描。利用衰减对比成像层析技术，克服了光学系统中x射线光束放大和样品旋转台的问题，在项目期末获得了小于100 nm的超高空间分辨率的三维结构。我们还对一些样品进行了空间分辨率约为0.5 μm的投影CT检测。样品的物理性质，如孔隙率和密度，是由宇宙尘埃样品的三维结构得到的。此外，还成功地获得了样品的分形维数。被认为来自彗星的宇宙尘埃的分形维数明显小于3。这可能是太阳系早期更多组成尘埃粒子聚集的证据。作为星尘号初检小组成员之一进行的星尘号样品分析，揭示了气凝胶收集器中撞击轨迹的三维结构和轨迹中的末端颗粒。这些结果为进一步详细的破坏分析提供了有关冲击过程的信息以及基本的纹理信息。结合红外天文观测，对宇宙尘埃矿物的红外光谱进行了实验研究，对宇宙尘埃进行了综合研究。此外，在SPring-8上开发了层析成像系统并对其性能进行了评价。定量制定了CT图像的亮度。利用这一公式，我们建立了一种利用减法对铁和碳元素进行三维元素映射的技术。结果应用于陨石和其他陆地样本以及宇宙尘埃样本。少

Three-dimensional structures of cosmic dust (interplanetary dust particles and unmelted micrometeorites) and cometary dust that was collected by NASA Stardust mission were examined using x-ray microtomography at SPring-8. Three-dimensional structures with ultra-high spatial resolution of less than 100 nm has been obtained at the end of the term of this project by imaging tomography using attenuation contrast by overcoming troubles in an optical system for enlargement of x-ray beams and a sample rotation stage. We have also examined some samples by projection CT with the spatial resolution of about 0.5 μm. Physical properties of the samples, such as porosities and densities, were obtained from the three -dimensional structures of the cosmic dust samples. Furthermore, fractal dimensions of the samples were successfully obtained. The fractal dimensions of cosmic dust which was considered to be derived from comets are significantly less than 3. This may suggest evidence of aggregation of c … More onstituent particles of the dust in the early stage of the solar system. The Stardust sample analysis, which was performed as one of the members of preliminary examination team of Stardust, revealed the three-dimensional structures of impact tracks in aerogel collectors and terminal particles in the tracks. These results gave information about the impact processes as well as basic textural information for further detailed destructive analyses. Experimental studies of infrared spectrum of cosmic dust minerals in connection with infrared astronomical observation have been also made for comprehensive research on cosmic dust. Furthermore, development of the tomography system at SPring-8 and evaluation of its performance have been done. Brightness of CT images was quantitatively formulated. By using this formulation, we have established a technique for three-dimensional element mapping of Fe and Cs using the subtraction method. The results were applied to meteorites and other terrestrial samples as well as cosmic dust samples. Less