Design And Fabrication Of Grating For Hard X-ray Phase Contrast Imaging

In inertial confinement fusion system, the density of pellet microspheres, which is used as a fuel, may be non-uniform after compression. The poor structure make pellet microspheres not being lit, which cannot lead to energy gain, thus leading to ignition failure. So it is very necessary to test the internal structure of pellet microspheres.Compared with traditional absorption imaging, X-ray grating phase contrast imaging can detect light elements and get absorbed, refracted and scattered information, thus showing more details. These advantages make it very promising to be widely applied in biomedical, nondestructive testing, materials science and other fields and a research hot topic in recent years as well. Phase grating and analysis grating are the core components of the X-ray grating phase contrast imaging system. It is necessary to design grating parameters and explore the fabrication technology manufacture craft.In this paper, phase grating and analyzer grating are designed according to the requirements of X-ray grating phase contrast imaging of pellet microspheres. Then, the gratings are successfully fabricated based on existing condition of our laboratory. The incident light energy of X-ray grating phase contrast imaging system in China is mainly between 20-30 keV, and the incident light energy what the paper choose is 40 keV, the space of light source to the phase grating is 200 mm.Firstly, The phase of the phase grating is ?, so the height is designed to be 51.67?m.Secondly, the period of the grating is 5?m according to the coherence requirements of the system and compact structure. Finally, The duty cycle is 0.5, because of the contrast of image and signal to noise ratio and its self-image distance, and the size is 10 × 10mm~2.However, the period of the analyzer grating is 2.52 ?m, which is the same as phase grating self-imaging when taking the geometrical amplification factor of the imaging system into consideration. And the hight of the analyzer grating is 51.89 ?m, which is determined by the absorption rate (30%). The duty cycle is 0.5, and the size is 15 × 15 mm~2on the basis of the image contrast and the noise ratio of signal.The phase grating and the analyzer grating are made according to the principle of anisotropic wet etching of silicon. The process of fabricating phase grating consists of three parts: the method for aligning interference fringes, grating mask making, increasing and anisotropic wet etching technique. While the process of fabricating the analyzer grating is based on the process of fabricating phase grating, adding thinning the substrate,anisotropic wet etching, Supercritical drying and electroplating. The difficulty lies in thinning the substrate and electroplating.Finally, The phase grating are Successfully fabricated. And fabrication of analysis grating have make progress in stages.