一种快速测量共聚焦X射线分析装置探测微元尺寸方法

共聚焦X射线荧光技术是一种无损的三维光谱分析技术，在材料，生物，矿物样品分析，考古，证物溯源等领域具有广泛应用。共聚焦X射线荧光谱仪的核心部件为两个多毛细管X光透镜。一个为多毛细管X光会聚透镜（PFXRL），其存在一后焦点，作用是把X光管所发出的发散X射线会聚成几十微米大小的高增益焦斑。另一透镜为多毛细管X光平行束透镜（PPXRL），其存在一几十微米大小前焦点，置于X射线能量探测器前端，其作用是接收特定区域的X射线荧光信号。在共聚焦Ｘ射线荧光谱仪中，PFXRL的后焦点与PPXRL的前焦点重合，所形成的区域称作探测微元。只有置于探测微元区域的样品能够被谱仪检测到，使样品与探测微元相对移动，逐点扫描，便能够对样品进行三维无损的X射线分析。探测微元的尺寸决定共聚焦X射线荧光谱仪的空间分辨率，因此精确测量谱仪的探测微元的尺寸是非常重要的。如图1所示，谱仪探测微元可以近似为椭球体，其尺寸可以用水平方向分辨率X, Y，和深度分辨率Z表示。目前，常采用金属细丝或金属薄膜通过刀口扫描的方法测量谱仪探测微元尺寸。为了精确的从三个维度测量探测微元尺寸，金属细丝直径要小于探测微元尺寸。金属细丝和探测微元都是数十微米级别的尺寸大小，很难把金属靠近探测微元。为了得到探测微元在不同X射线能量下尺寸变化曲线，要采用多种金属细丝测量。采用单个金属细丝依次测量比较耗费时间。采用金属薄膜可以很方便地测量探测微元的深度分辨率Z，但是当测量水平分辨率X, Y时，难以准确测量。为了解决以上谱仪探测微元测量中存在的问题，本文提出采用多种金属丝平行粘贴在硬纸片上作为样品用于快速测量探测微元尺寸。附有金属细丝的硬纸片靠近谱仪探测微元，可以将探测微元置于硬纸片所在平面。由于硬纸片与金属细丝在同一水平面，在谱仪摄像头的协助下，可以把金属细丝迅速的靠近探测微元。靠近探测微元后，在全自动三维样品台的协助下，金属细丝沿两个方向对探测微元分别进行一次二维扫描。通过对二维扫描数据的处理便可以获得探测微元尺寸随入射X射线能量变化曲线。采用此方法对实验室所搭建的共聚焦X射线荧光谱仪的探测微元进行了测量。

A Method Quickly to Measure the Size of the Confocal Volume of Confocal X-Ray Instrument

Confocal X-ray fluorescence is a directly non-destructive analysis technique with spatial resolution, widely used in materials, biology, mineral sample analysis, archaeology, evidence traceability and other fields. The confocal X-ray fluorescence spectrometer work is based on a polycapillary X-ray lens. A polycapillary focusing X-ray lens (PFXRL) attached to the X-ray tube is used to focus the divergent X-ray from the X-ray tube to the output focal spot with dozens of micron diameter and high power density gain. A polycapillary parallel X-ray lens (PPXRL) with an input focal spot placed on the front of the silicon drift detector is used to receive the fluorescence signal from the specific region. The overlap region of the output focal spot of the PFXRL and the input focal spot of the PPXRL in the confocal X-ray fluorescence spectrometer is called probe volume. Only the sample in the probe volume can be detected. The spatial information of the sample can be obtained by the relative movement of the probe volume and sample point by point. The size of the probe volume determines the spatial resolution of the confocal X-ray fluorescence spectrometer. Thus, it is significant to measure the size of the probe volume. The shape of the probe volume is similar to an ellipsoid. The size of the probe volume can be expressed as the horizontal resolution X, Y and the depth resolution Z, as showni n Fig.1. The detail size of the probe volume of the confocal X-ray instrument is commonly measured by the metal wire ormetal film using the knife scanning method. To precisely measure the probe volume size, the diameter of the metal wire prefer small than the probe volume size. It is difficult to place the metal wire close to the probe volume because the probe volume size and mental wire diameter are dozens of microns. According to obtain the changing curve of the probe volume size and the energy of the incident X-ray beam, various metal wires were used, which is a waste of time. The metal film is suitable for measuring the depth resolution of the probe volume (Z). However, it is difficult for the metal film to measure the horizontal resolution of the probe volume (X, Y). To solve the problem mentioned above, a special sample of series metal wires stick on paper was used to measure the size of the confocal volume of the confocal X-ray instrument. To adjusting the special sample close to the probe volume, the probe volume can be placed in the plane of the paper. With the assistance of the digital camera, the metal wire can be rapidly placed close to the probe volume. After putting the metal wire close to the probe volume, two-dimensional scanning is performed along with two directions of the probe volume with the help of the motorized translation stage. The changing curve of the probe volume and incident X-ray energy was obtained by processing the data obtained from the two-dimensional scanning. In this study, the probe volume size of the confocal X-ray instrument in our laboratory was measured by the method proposed above.