本文選題：X射線相襯成像 + 微結(jié)構(gòu)X射線源��； 參考：《深圳大學(xué)》2017年碩士論文

【摘要】：目前,限制X射線相襯成像向應(yīng)用化發(fā)展的主要阻力是缺乏高亮度高相干的微結(jié)構(gòu)X射線源,而新型微結(jié)構(gòu)X射線源可以提供高空間相干的X射線光束,因此近年來它成為X射線相襯成像光源的研究熱點(diǎn)。然而,由于國內(nèi)外對入射電子在陽極靶內(nèi)的電子沉積能量分布研究相對較少且研究不夠深入,因此研究人員在設(shè)計微結(jié)構(gòu)X射線源時,只能通過自身的經(jīng)驗結(jié)合電子射程經(jīng)驗公式值來確定具體參數(shù),因而無法提高設(shè)計效率和避免較大的設(shè)計誤差。更重要的是,微結(jié)構(gòu)X射線源中微米級結(jié)構(gòu)與尺寸對出射的X射線強(qiáng)度和角分布起到至關(guān)重要的影響,因此如何進(jìn)一步研究高能電子與陽極靶作用的電子軌跡及能量沉積分布成為了亟待解決的問題。本文根據(jù)電子的多重散射理論,并基于蒙特卡羅方法進(jìn)行數(shù)值計算,模擬了高能電子在鎢、鉬、銅、金剛石中的電子軌跡和沉積能量分布(代表電子入射到陽極靶后熱能分布和初始的X射線強(qiáng)度分布)。計算結(jié)果表明:99%電子能量沉積在近似圓柱形區(qū)域內(nèi),相對于靶面上的電子束斑,當(dāng)電子與靶原子作用時,產(chǎn)生X射線的區(qū)域更大(即X射線有效焦斑遠(yuǎn)大于電子束斑),其區(qū)域大小受到入射電子能量、靶材料等因素影響。同時,通過實驗發(fā)現(xiàn)電子在入射方向上的沉積能量分布是會隨著深度增加而加強(qiáng),當(dāng)?shù)揭欢ㄉ疃群蟛艜霈F(xiàn)遞減,即沉積能量峰值點(diǎn)在距表面一定深度處。另外,在相同能量電子入射下,峰值點(diǎn)處沉積的能量不完全與靶材原子序數(shù)和密度呈正相關(guān),如金剛石原子序數(shù)和密度遠(yuǎn)小于鉬和銅,但金剛石的峰值點(diǎn)能量反而更高。然后,通過結(jié)合四種靶材的模擬結(jié)果和杜隆-柏替定理,我們得到不同陽極靶在20~100keV電子入射下所能承受的陽極臨界電流值,它按高低排列依次是金剛石、鉬、銅、鎢。通過對比分析,我們發(fā)現(xiàn)5μm厚度的鎢靶能夠吸收能量為100keV的電子99%的能量,非常適合作為微結(jié)構(gòu)靶,而金剛石膜的陽極臨界電流最高,作為熱沉材料有很大的潛力。在此基礎(chǔ)上,本文深入研究了周期為3μm、占空比為1:3的微結(jié)構(gòu)鎢靶中出射X射線強(qiáng)度的角分布和光譜與入射電子能量、靶厚度的關(guān)系,發(fā)現(xiàn)微結(jié)構(gòu)鎢靶出射的X射線強(qiáng)度角分布呈高斯分布,X-ray主要集中在+Z方向±15o區(qū)域內(nèi),且Z=50cm處垂軸平面上的X射線分布類似于“M”型。因此,本文計算結(jié)果對于微結(jié)構(gòu)X射線源和10μm以下、高亮度微焦斑X射線源的設(shè)計研究提供極為有價值的參考。
[Abstract]:At present, the main resistance to the development of X-ray phase contrast imaging is the lack of high brightness and high coherence microstructural X-ray sources, and the new microstructured X-ray sources can provide highly spatially coherent X-ray beams. Therefore, in recent years, it has become the research hotspot of X-ray phase contrast imaging light source. However, because the energy distribution of incident electron deposition in anode target is less studied at home and abroad, the researchers design microstructural X-ray source. The parameters can only be determined by combining their own experience with the empirical formula value of electron range, so the design efficiency can not be improved and large design errors can be avoided. More importantly, the micron structure and size of the microstructural X-ray source play a crucial role in the intensity and angular distribution of the emitted X-ray. Therefore, how to further study the electron trajectory and energy deposition distribution of high energy electron and anode target is an urgent problem to be solved. Based on the theory of multiple scattering of electrons and Monte Carlo method, the high energy electrons in tungsten, molybdenum and copper are simulated. The electron trace and deposition energy distribution in diamond (representing the thermal energy distribution and the initial X-ray intensity distribution after the electron incident to the anode target). The calculated results show that the electron energy of: 99% is deposited in an approximate cylindrical region, relative to the electron beam spot on the target surface, when the electron acts with the target atom, The region producing X-ray is larger (that is, the effective focal spot of X-ray is much larger than that of electron beam), and the size of the region is affected by the incident electron energy, target material and other factors. At the same time, it is found that the distribution of electron deposition energy in the incident direction will be strengthened with the increase of depth, and will decrease only after a certain depth, that is, the peak point of deposition energy is at a certain depth from the surface. In addition, at the same energy electron incidence, the energy deposited at the peak point is not completely correlated with the atomic number and density of the target, such as diamond atomic number and density is much smaller than that of molybdenum and copper, but the peak energy of diamond is higher. Then, by combining the simulation results of four kinds of targets and the Duron-Berti theorem, we obtain the anode critical current values of different anode targets under the electron incidence of 20 ~ 100keV, which are diamond, molybdenum, copper and tungsten in order of high and low. By comparison and analysis, we find that tungsten target with 5 渭 m thickness can absorb 99% of electron energy of 100keV, which is very suitable for microstructural target, while the anode critical current of diamond film is the highest, which has great potential as heat sink material. On this basis, the angular distribution of X-ray intensity and the relationship between X-ray intensity and electron energy and target thickness in micro-structured tungsten target with a period of 3 渭 m and a duty cycle of 1:3 have been studied. It is found that the X-ray intensity angle distribution of the micro-structure tungsten target is mainly in the Z direction 鹵15o region, and the X ray distribution on the vertical plane at 50 cm is similar to that of "M" type. Therefore, the calculated results in this paper provide a valuable reference for the design and study of microstructural X-ray sources and X-ray sources with high brightness and microfocal spot below 10 渭 m.
【學(xué)位授予單位】：深圳大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O434.1

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