一种毛细管聚焦的便携式微束X射线荧光谱仪

基于毛细管X光透镜技术的便携式能量色散X射线荧光分析因其无损分析等优点成为分析文物样品的有利工具。但由于文物样品的表面不平整或弧度以及毛细管X光透镜聚焦X射线的特点,导致在测量过程中样品测量点与毛细管X光透镜出端之间的距离产生变化,引起照射样品的X射线束斑大小发生改变,从而影响测量结果的准确性和元素区域扫描的分辨率。介绍了本实验室自行研发的一种新型便携式微束X射线荧光谱仪,此谱仪主要是由SDD X射线探测器、30W低功率X射线管、毛细管X光透镜、CCD和一个新型闭环控制系统构成。该闭环控制系统是在激光位移传感器能够精确控制样品测量点到毛细管X光透镜出端距离的基础上,结合LabVIEW语言环境下开发的计算机控制程序以及步进电机、样品台等器件组成。基于此系统,该实验室研发的便携式微束X射线荧光谱仪在测量过程中可以时刻保证照射样品的X射线光斑大小固定不变。同时,该谱仪还可以通过调整样品测量点到透镜出端的距离来选择不同尺寸的X射线照射光斑。为了验证设备的可行性,使用该便携式微束X射线荧光谱仪在激活激光位移传感器和关闭激光位移传感器两种情况下测量了一块表面不平整古陶瓷样品釉彩层中K,Ca,Zn和Fe等元素的含量及分布,并将测量结果进行了对比。结果显示,在激活激光位移传感器的情况下测得的样品微区元素含量与真实值较接近,扫描区域元素分布图的分辨率更好,表明本谱仪基于激光位移传感器开发的自动调整样品测量点到透镜出口端距离的闭环控制系统能有效的减少由于样品表面不平整或弧度带来的测量误差,弥补了现有微束X射线荧光谱仪在此方面的不足。因此,本便携式微束X射线荧光谱仪在无损分析检测文物方面具有潜在的应用前景。

A New Type of Portable Micro-X-Ray Fluorescence Spectrometer with Polycapillary Optics

The portable micro-X-ray fluorescence analysis with polycapillary optics has advantages of being non-destructive, and it has been widely used in the analysis of cultural relics. However, due to the irregular or curving surface of archaeological objects and the shortcoming of polycapillary optics in focusing X-rays, the distances between the irradiation spot of samples and exit of polycapillary optics are variables. As a result, the sizes of focused X-ray spot can't keep constant, which reduces the accuracy of measurement and the resolution of elemental mappings of scanning area. In this paper, we propose a new type of portable micro-X-ray fluorescence spectrometer that consists of a new closed loop feedback system and SDD X-ray detector, 30W lower power X-ray tube, polycapillary optics, CCD and so on. In particularly, the closed loop feedback system is composed of Laser Displacement Sensor (LDS), stepper motor, sample stage and computer programs developed by LabVIEW languages. During measuring, the LDS accurately controls the distances between the irradiation spot of samples and exit of polycapillary optics. Based on this closed loop feedback system, our portable micro X-ray fluorescence spectrometer can keep the sizes of focused X-ray spot constant. On the other hand, we provide different alternative sizes of focused X-ray spot by controlling the distances between the exit of polycapillary optics and measured spot of samples in our spectrometer. In order to test the feasibility of this instrument, the concentration of elements and elemental mappings of K, Ca, Zn, Fe and other elements in the irregular colored glaze of a piece of ancient porcelain have been measured by our portable micro X-ray fluorescence spectrometer under enabling and disabling LDS conditions. From the results, it can be concluded that the concentration of elements is very close to the real values and the resolution of elemental mappings is better when LDS is enabled. This indicates that the closed loop feedback system based on LDS can accurately reduce the measurement errors caused by the irregular or curving surface of archaeological objects. Therefore, this portable micro X-ray fluorescence spectrometer developed by our laboratory has potential application prospects in non-destructive analysis of cultural relics.