硅漂移探测器中逃逸峰的分析与计算

Analysis and Calculation of Escape Peaks in Silicon Drift Detectors

能量色散X射线荧光光谱所使用的硅漂移探测器(SDD)在检测过程中会在个别含量较高待测元素所产生的较强特征峰的低能侧形成逃逸峰,其相应的特征峰也会损失一部分强度,逃逸峰的产生位置与探测器的成分有关;SDD探测器中入射特征峰与逃逸峰之间的能量差值为1.739 keV,等于硅原子的K_(α)特征能量,逃逸峰的强度与入射X射线的强度成正比,即与相应元素的含量/特征峰强度成正比,通常的入射特征峰逃逸概率比较低,在逃逸峰强度较低时对测试结果影响较小,当基体元素含量较高时产生的逃逸峰较大就会导致测试结果偏差较大;通过理论计算可以看出,逃逸峰的产生概率与探测器角度及元素种类等条件有关,从硅原子的质量吸收系数的变化趋势可以发现,随着入射特征线能量的增大硅原子对其的质量吸收系数降低,相应入射线的逃逸峰产生概率也会降低。当逃逸峰与其他待测元素的特征能量峰位置有重合时,会干扰相应元素的准确测量,导致相应元素的特征峰强度偏大,尤其是当待测元素含量较低时,其产生的特征峰强度较小,逃逸峰导致的本底强度所产生的干扰相对更大,因此需要对逃逸峰进行准确计算和校正。搭建了相应的平台进行测试,并以Fe和Mn元素为例,通过对SDD探测器中两种元素产生的逃逸峰概率进行理论分析与计算,并与实际测试谱图得到的逃逸概率值进行对比,发现两种数据符合较好,并且经对比发现在Fe_(2)O_(3)样品中的Fe∶K_(β)线的逃逸峰与Cr∶K_(α)峰重合,Fe∶K_(α)线的逃逸峰与Ti∶K_(α)峰有部分重合,在扣去逃逸峰后可以降低检出限,以更好地对Cr和Ti进行准确定量,该方法可扩展到其他含量较高元素的逃逸峰计算与校正,尤其是在土壤、矿物、合金检测等个别元素含量较高的样品中多元素检测方面的应用,可提高X射线荧光方法的测试准确度。

During the detection process,the silicon drift detector(SDD)used in energy-dispersive X-ray fluorescence spectrometry will form escape peaks on the low-energy side of the solid characteristic peaks generated by the individual elements to be measured with high content,and the corresponding characteristic peaks are also will lose some strength,and the location of the escape peak is related to the composition of the detector.The energy difference between the incident characteristic peak and the escape peak in the SDD detector is 1.739 keV,which is equal to the K_(α)characteristic energy of the silicon element.The intensity of the escape peak is proportional to the intensity of the incident X-ray,that is,proportional to the content of the corresponding element/characteristic peak intensity.The escape probability of the incident characteristic peak is usually low,and the influence on the test results is small when the escape peak intensity is low.It can be seen from theoretical calculations that the probability of generating escape peaks is related to the detector angle and element types,and with the increase of the incident characteristic line energy,the mass absorption coefficient of the silicon atom and the corresponding escape peak generation probability will also reduce.When the escape peak coincides with the characteristic energy peaks of other elements to be measured,it will interfere with the accurate measurement of the corresponding element,especially when the content of the element to be measured is low.The interference will be relatively more significant.Therefore,it is necessary to calculate and correct the escape peak accurately.In this paper,a corresponding platform is built for testing,and taking Fe and Mn elements as examples,through theoretical analysis and calculation of the escape peak probability in the SDD detector and compared with the escape probability value obtained from the actual test spectrum,it is found that the two data are in good agreement,and after the comparison it was found that the escape peak of Fe∶K_(β)line in Fe_(2)O_(3)sample overlapped with Cr∶K_(α)peak,and the escape peak of Fe∶K_(α)line partially overlapped with Ti∶K_(α)peak.After deducting the escape peak,Cr and Ti can be better analyzed for accurate quantification.This method can be extended to the calculation and correction of escape peaks of other elements with higher content,especially in the application of multi-element detection in samples with high content of individual elements such as soil,mineral,alloy detection,etc,and improve the test accuracy of X-ray fluorescence method.