ABSTRACT
A structured double-period CsI scintillation screen was successfully developed to improve its detection efficiency based on an oxidized silicon micropore array template with a period value on the order of micro-scale. The structure comprises a main structure along with a sub-structure. The main structure with a period of 8â µm was arranged in a square array consisting of square columnar scintillator units. The micropore walls between the main structure units were purposely fabricated from a SiO2-Si-SiO2 layered structure. The pore walls in commonly used single-structure with a period of 4â µm use the same layered structure composition to obtain a fair comparison. The thickness of both Si and the SiO2 layers was around 0.4â µm. The unique feature of the double structure lies in the even separation of each unit within the main structure into four square columnar scintillator sub-units. These four sub-units within each sub-structure were isolated solely by SiO2 layers with a thickness of approximately 0.8â µm. As a result, the X-ray-induced optical luminescence intensity of the double-structure screen exhibited a 31% increase compared to the corresponding single-structure scintillation screen. In X-ray imaging, a spatial resolution of 109 lp/mm was achieved, which closely matched the results obtained with the single-structure CsI screen. Furthermore, the detective quantum efficiency also displayed a notable improvement.
ABSTRACT
Structured scintillation screen based on oxidized Si micropore array template can effectively improve the spatial resolution of X-ray imaging. The purpose of this study is to investigate the effect of SiO2 layer thickness on the light guide and X-ray imaging performance of CsI scintillation screen when the structural period is as small as microns. Cylindrical micropores with a period of 4.3â µm, an average diameter of 3.3â µm and a depth of about 40â µm were prepared in Si wafers. SiO2 layer was formed on the pore walls after thermal oxidation. Increasing SiO2 layer thickness would be beneficial to the propagation of scintillation light along the cylindrical channels. What was not previously anticipated was that the pore size gradually shrank as the SiO2 layer thickened. The pore shrinkage would reduce the filling rate of CsI in the templates and thus would reduce the production of scintillation light. The structured CsI scintillation screens with different SiO2 layer thicknesses were fabricated by filling CsI scintillator into the oxidized silicon micropore array template. The morphology, crystallinity, X-ray excited optical luminescence, and X-ray imaging performance of the screens were studied. The results show that the spatial resolutions of X-ray images measured using the structured CsI scintillation screens with different SiO2 layer thicknesses are close to each other, and they are all about 110 lp/mm. However, the X-ray excited optical luminescence of the screen and detective quantum efficiency of X-ray imaging vary with the thickness of the SiO2 layer. The optimal thickness is about 350â nm.
ABSTRACT
To obtain better light guidance and optical isolation effects under a limited microcolumn wall thickness, the influence of the thickness of a SiO2 reflective layer on the performance of a structured CsI(Tl) scintillation screen based on an oxidized Si micropore array template in X-ray imaging was simulated. The results show that the SiO2 reflective layer should maintain a certain thickness to achieve good light-guide performance. However, if the template is entirely composed of SiO2, the light isolation performance of the microcolumn wall will be slightly worse. The results provide a basis for optimizing the thickness of SiO2 reflective layer.
