發(fā)布時間：2018-03-14 11:40

  本文選題：X射線探測　切入點：Cs　出處：《電子科技大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：X射線探測器在安全檢察、醫(yī)學(xué)成像、空間探測等眾多領(lǐng)域都有廣泛應(yīng)用。作為探測器最重要部分的轉(zhuǎn)換屏,其材料的光轉(zhuǎn)換效率對整個系統(tǒng)起著決定性的作用。在本文中,我們提出了一種新的集成化X射線探測器。我們選用CsI:Tl作為熒光轉(zhuǎn)換屏材料,PIN或者CCD作X射線探測系統(tǒng)中的熒光接收器件,采用真空熱蒸發(fā)法將CsI:Tl晶體制備成呈晶柱狀結(jié)構(gòu)的薄膜并直接集成在CCD或者PIN上。為了抑制熒光擴散和晶柱間發(fā)生串?dāng)_,我們在Cs I:Tl閃爍晶體膜表面鍍一層Al膜來對晶柱狀的薄膜進行包裹和隔離,從而起到保護作用。本文的主要內(nèi)容如下:按照從簡單到復(fù)雜的順序分別建立了三種理論模型:理想連續(xù)層模型、理想晶體單元模型和具有理想晶柱結(jié)構(gòu)的薄膜模型。針對Cs I:Tl閃爍晶體薄膜的熒光轉(zhuǎn)換因子與薄膜各結(jié)構(gòu)參數(shù)的關(guān)系我們用MATLAB軟件進行了仿真計算。仿真結(jié)果表明:CsI:Tl閃爍晶體薄膜厚度在400μm處時熒光轉(zhuǎn)換因子最大;具有晶柱結(jié)構(gòu)的薄膜的熒光轉(zhuǎn)換因子明顯高于無晶柱結(jié)構(gòu)的薄膜的熒光轉(zhuǎn)換因子;入射X光子能量越低,CsI:Tl晶體的最佳厚度越薄,反則反之。通過理論計算,我們在實際中采用了真空熱蒸發(fā)法分別在Si和玻璃基片上沉積并生長CsI:Tl薄膜,并對Cs I:Tl薄膜的表面微結(jié)構(gòu)和光學(xué)特性進行了測試和分析。結(jié)果表面:采用真空熱蒸發(fā)法制備的Cs I:Tl薄膜沿(200)晶面擇優(yōu)生長,其晶體結(jié)構(gòu)擇優(yōu)取向生長與厚度關(guān)系密切,厚度相對較小時存在明顯擇優(yōu)取向生長,隨著膜厚增加晶體生長擇優(yōu)取向現(xiàn)象明顯減弱;蒸發(fā)速率越大,CsI:Tl薄膜的相對光輸出強度越小;對于不同退火處理的薄膜樣品,當(dāng)在250℃退火時,缺陷得到改善,薄膜樣品的結(jié)晶質(zhì)量達到較好的程度,相對光輸出也增加;通過改變鍍膜的工藝方法,有效的改善薄膜的結(jié)晶質(zhì)量。通過搭建樣品的成像測試平臺,測試了樣品的光轉(zhuǎn)換率、定性地測試了樣品的空間分辨率。通過選擇合適的沉積速率、通過合適的退火溫度退火、調(diào)節(jié)薄膜厚度和薄膜微結(jié)構(gòu)、利用預(yù)沉積手段來獲得光轉(zhuǎn)換效率高、空間分辨率高的閃爍屏,以提高閃爍成像探測器的成像質(zhì)量。
[Abstract]:X-ray detectors are widely used in many fields, such as safety inspection, medical imaging, space detection and so on. As the most important part of the detector, the optical conversion efficiency of the material plays a decisive role in the whole system. We propose a new kind of integrated X-ray detector. We choose CsI:Tl as the fluorescent conversion screen material or CCD as the fluorescence receiver in the X-ray detection system. The thin films with columnar structure of CsI:Tl crystals were prepared by vacuum thermal evaporation and directly integrated into CCD or PIN. We have coated a layer of Al film on the surface of Cs I: TL scintillator film to wrap and isolate the columnar film. The main contents of this paper are as follows: according to the order from simple to complex, three theoretical models are established: ideal continuum model. Ideal crystal unit model and thin film model with ideal crystal column structure. The relationship between the fluorescence conversion factor of Cs I: TL scintillator thin film and the structure parameters of the thin film has been simulated by MATLAB software. The simulation result table is given. When the thickness of the thin film is 400 渭 m, the maximum fluorescence conversion factor is obtained. The fluorescence conversion factor of the thin film with crystal column structure is obviously higher than that of the film with no crystal column structure, the lower the incident X photon energy is, the thinner the optimum thickness of CsI: TL crystal is. In practice, CsI:Tl thin films were deposited and grown on Si and glass substrates by vacuum thermal evaporation, respectively. The surface microstructure and optical properties of Cs I: TL thin films were measured and analyzed. Results: the surface of Cs I: TL thin films prepared by vacuum thermal evaporation method has preferential growth along the crystal plane. The preferred orientation growth of the crystal structure is closely related to the thickness of Cs I: TL thin films. With the increase of film thickness, the preferred orientation phenomenon of crystal growth is obviously weakened, the higher the evaporation rate is, the smaller the relative light output intensity of CsI: TL thin films is, and for different annealed films, the preferred orientation of CsI: TL thin films is decreased with the increase of film thickness. When annealed at 250 鈩，

本文編號：1611098