【作者】 王雷；

【导师】 葛良全； 张庆贤；

【作者基本信息】 成都理工大学 ， 核废物地质处置工程， 2016， 硕士

【摘要】 微型透射式X射线管广泛使用于EDXRF分析领域,具有体积小、功耗低、X射线照射量率高、不使用时无辐射危险等显著的优点,可作为便携式EDXRF分析仪的激发源。微型透射式X射线管结构复杂,内部为真空状态,在狭小的空间内集成了电子发射装置、电磁聚焦系统、靶材及出射窗,外接高压供电装置及阴极电流提供装置,属于精密器件,造价昂贵。微型透射式X射线管的基本原理是阴极发射电子,通过阴极和阳极间的高压电场加速,轰击阳极上的靶材,从而产生X射线。电子轰击靶材将产生能量连续的韧致辐射,靶材发出的特征X射线叠加在韧致辐射谱线上,形成微型透射式X射线管原级谱。在EDXRF分析中,需要的初级X射线能量必须大于目标元素原子的吸收限,在吸收限以下的初级X射线将成为X射线仪器谱的本底。较高照射量率的吸收限下初级X射线不仅会影响EDXRF分析的精确度和灵敏度,使EDXRF分析难度增加;甚至可能会造成电子学线路计数过载。因此,在ED XRF分析中希望尽可能减少吸收限下的初级X射线照射量率,同时又必须保证吸收限上的初X射线具有较高的照射量率。本论文选题来源于国家重大科研装备研制项目“深部资源探测核心装备研发”(项目编号:ZDYZ2012-1)和国家高技术研究发展计划(863计划)资源环境技术领域主题项目课题“高精度射线能谱探测仪器研发”(课题编号:2012AA061803)。本文从EDXRF分析的实际需要出发,研究微型透射式X射线管出射谱线的特征,并尝试在微型透射式X射线管的出射孔外放置滤光片,以达到减少吸收限以下的初级X射线照射量率的同时,保证吸收限以上的X射线有较高的照射量率。本文以10KeV能量为突变点,根据物质对X射线的吸收特性,选取金属铝作为滤光片的基材,铜、镍、锌三种金属元素作为滤光片的添加材料,研究不同添加元素含量和不同厚度滤光片对微型透射式X射线管出射谱的影响。通过理论计算分析了铝合金滤光片对微型透射式X射线管出射谱线的影响,并依据理论分析建立蒙特卡洛模型,进行模拟。根据蒙特卡洛模拟的结果,得出了铝-铜合金、铝-镍合金、铝-锌合金最佳的搭配比例及滤光效果,结论如下:铝-铜合金作为滤光片材料时,最佳的铜含量为10%,最佳的铝-铜合金厚度为150um,此时能量在0~10KeV范围内的X射线记数仅有能量在10~35KeV范围内的X射线记数的4.97%,兼顾了10~35KeV能量范围内的X射线照射量率和减少0~10KeV范围内的X射线照射量率的要求。铝-镍合金作为滤光片材料时,最佳的镍含量为10%,最佳的铝-镍合金厚度为100um,此时能量在0~10KeV范围内的X射线记数仅有能量在10~35Ke V范围内的X射线记数的7.37%。铝-锌合金作为滤光片材料时,最佳的锌含量为15%,最佳的铝-锌合金厚度为100um,此时能量在0~10KeV范围内的X射线记数仅有能量在10~35KeV范围内的X射线记数的10.7%。更多还原

【Abstract】 The miniature transmission X-ray tube is widely used in energy dispersive X-ray Fluorescence Analysis(EDXRFA). The miniature transmission X-ray tube with a small,low power consumption, X-ray emission efficiency that can be made the excitation source of handheld X-ray energy dispersive fluorescence analyzer. Miniature transmission X-ray tube is a vacuum state inside with complex structure. In the small space integrated electronemitting device, a magnetic focusing system, target and exit window. Miniature transmission X-ray tube add high voltage power supply device and a cathode current supply means. It is a precision and expensive device.The basic principles of Miniature transmission X-ray tube is a cathode emits electronsby high voltage electric field between the cathode and anode acceleration,bombarding the target on the anode to produce X-rays. Energy electron bombardment target will produce a continuous bremsstrahlung, characteristic X-rays emitted by the target brems-strahlung spectrum superimposed on the formation of Miniature transmission X-ray tube primary level spectrum. In EDXRF analysis, primary X-ray energy is usually required in the absorption limit must be greater than the atomic absorption of the target element. The primary X- ray below the absorption limit will be the background of the X- ray instrument spectrum. Relatively high radiation absorption limit rate of primary X-ray will not only affect the accuracy and sensitivity EDXRF analysis, so EDXRF analysis more difficult, and may even cause the detector electronics line load is too high.Thus, in EDXRF Analysis want to minimize the exposure rate of absorption limited primary, meanwhile must ensure that absorption limit above primary X-rays with higher volume ratio.The thesis stems from major national scientific research equipment development project "deep resource exploration core equipment research and development"(item number: ZDYZ2012-1) and National High Technology Research and Development Program(863 Program) resource environmental technology issues relating to the project "high-precision ray spectroscopy detection equipment research and development "(project number: 2012AA061803).From EDXRF analysis of actual needs, research miniature transmission X-ray tube emission spectrum characteristics, and try to miniature transmission X-ray tube is placedoutside the exit aperture filter, in order to reduce X-ray dose below absorption limit rate, At the same to ensure that the above absorption limit X-ray have a higher exposure rate. According to the X-ray absorption characteristics of the material, the selected aluminum as the base metal, copper, nickel, zinc, three metal filter element is added as a filter material of different content of the alloy and the thickness of the different miniature transmission X ray tube influences emission spectrum.Through theoretical calculation and analysis of the aluminum filter for Miniature transmission X-ray tube influences emission spectrum, based on the theoretical analysis of the establishment of the Monte Carlo model for simulation. According to the results of Monte Carlo simulation, drawn aluminum-copper alloys, aluminumnickel alloys,aluminum- zinc alloy optimal mix ratio and optical effect, the following conclusions:aluminum- copper alloy is used as filter material, most copper content of 10%, the best of aluminum- copper alloy having a thickness of 150 um, this time energy X-raycounts in the range of 0 ~ 10 KeV only energy X-ray counts in the range of 10 ~ 35 KeV 4.97%, taking into account the X-ray exposure rate and reduce X-ray exposure rate is within the range of 0 ~ 10 KeV request within 10 ~ 35 KeV energy range. Alum-inum- nickel alloy is used as filter material, optimal nickel content of 10%, the best aluminum- nickel alloy having a thickness of 100 um, energy is in the 0 ~ 10 KeV X-ray counts only the energy range 7.37%,X-ray count within 10~ 35 KeV range. Aluminum- zinc alloy is used as filter material, the best zinc content of 15%, the best aluminum- zinc alloy having a thickness of 100 um, energy is now in the range of 0 ~ 10 KeV count X-ray energy in onl-y 10.7%,X-ray count within 10~ 35 KeV range.更多还原