Research On X-ray Scintillation Screen Technology Based On Silicon Microchannel Array

With the development of X-ray imaging technology,high luminous efficiency and high detection efficiency have become the main performance requirements of the core device of X-ray imaging system.The traditional thin film columnar scintillation screen has problems such as crystal column adhesion,which will cause optical crosstalk,resulting in limited spatial resolution of the scintillation screen.Although the spatial resolution of the scintillation screen can be guaranteed by reducing the thickness of the scintillation screen,this will affect the detection efficiency of the scintillation screen.In order to ensure the detection efficiency and achieve high resolution,X-ray scintillation screen based on microchannel array came into being.This structure can improve the spatial resolution of the scintillation screen without affecting the detection efficiency.In this paper,X-ray scintillation screen technology based on silicon microchannel array is studied.The basic theory of CsI（Tl）scintillation screen luminescence is studied.The interaction between X-ray and CsI（Tl）scintillation crystal is analyzed.The three main modes of action of photoelectric effect,Compton scattering and electron pair effect are described in detail.The luminescence principle of CsI（Tl）scintillation crystal is explained from the perspective of energy band.The working principle of CsI（Tl）scintillation screen based on silicon microchannel array is introduced.The transmission process of fluorescent photons in the channel is analyzed,and a method to improve the transmission efficiency of fluorescent photons is proposed.The model construction and simulation of X-ray CsI（Tl）scintillation screen based on silicon microchannel array were completed by using Geant4 software.The effects of X-ray energy,scintillation screen hole depth,silicon wall thickness and reflector material on the bottom light output of X-ray CsI（Tl）scintillation screen were studied.The simulation results show that the larger the hole depth,the more the output photons;increasing the X-ray energy,the number of output photons at the bottom will increase rapidly and gradually decrease after reaching the peak.As the thickness of the silicon wall increases,the suppression of the scintillation crosstalk between adjacent CsI（Tl）micropillars increases,and the number of output photons at the bottom of the scintillation screen decreases.The lower the refractive index of the reflective layer material on the inner wall of the channel,the higher the number of output photons at the bottom.The silicon microchannel array substrate with a period of 10μm and a channel depth of about 320μm was prepared by lithography,ICP etching,silicon anisotropic wet etching,light-assisted electrochemical etching,and shaping.The effect of shaping time on the morphology of silicon microchannel array substrate was studied.The relationship between the dry oxidation time of silicon and the thickness of Si O₂ reflective layer was studied.The filling process of CsI（Tl）was studied,and the reasons for the existence of voids at the bottom of the channel were analyzed.The results show that the filling effect of high vacuum and low filling rate is better.The CsI（Tl）scintillation screen based on silicon microchannel array was successfully prepared by vacuum melting filling method.The X-ray scintillation screen imaging test device was built,and the physical imaging test was carried out.The effects of silicon wall thickness,Si O₂ reflective layer thickness and filling temperature on the performance of scintillation screen were studied.The results show that the imaging brightness of CsI（Tl）scintillation screen decreases with the increase of silicon wall thickness.With the increase of the thickness of the Si O2 reflective layer,the imaging brightness of the CsI（Tl）scintillation screen increases.The brightness and luminous uniformity of the scintillation screen with a filling temperature of 660℃ are higher than those of the scintillation screen with a filling temperature of 630℃ and 690℃.