滤片对能量色散X射线荧光光谱方法测定轻基体中痕量重金属Cd元素的作用

摘要

Increasing the ratio of peak to back (P/B)value is of great importance when using energy dispersive X-ray fluorescence spectrometry to detect heavy metal elements in the light-matrix.Setting up the filters is one way to solve this problem.In the paper the choices (material elements and thickness) for primary filter(it can be divided into One primary filter and Two primary filter) and secondary filter(balance filter) were analyzed ,then the Monte Carlo simulation was carried out by MC software ,and the accuracy of theoretical analysis was verified by comparing the P/B value before and after setting up.The One primary filter simulation sets up Fe and Cu two kinds of materials.The results show that the biggest P/B values all increases two times after setting up primary filters while the value is 1.36 before setting up;The Two primary filter simulation sets up Te and Ba two kinds of materials.The biggest P/B values are 14.88 and 13.58 ,which all significantly increase almost 10 times than the previ-ous setting up;The balance filter sets up Rh and Ru two filters ,the balancepassband is obtained through two count subtraction. The results show that in the passband the transmission rate of the characteristic peaks is 83.1％ ,while outside the band the background value is reduced to almost 0 ,and the P/B values increase greatly.It is found that setting up the three kinds of filters effectively increases the P/B values ,in which the balance filter is the most powerful ,the Two primary filter is the second ,and the One primary filter is the least.The three kinds of filters can be set up at the same time in order to further increase the P/Bvalue in theory ,but the Cd amounts in light matrix are trace ,so that the low count result will greatly increase the radioactive statistical fluctuation error ,therefore ,in the practical application ,this point should also be considered to decide whether two fil-ters are set up at the same time ,or three are set up at the same time.The innovation of this paper lies in the application of the Two primary filter in addition to the traditional two filters.%用能量色散X射线荧光光谱方法检测轻基体中重金属元素时,提高峰背比是一大难题,而设置滤片是解决这个难题的一种办法.该研究先对初级滤片(分为一类初级滤片和二类初级滤片)和次级滤片(平衡滤片)的选择(材料元素及厚度)作了理论分析,然后通过MC软件进行蒙特卡罗进行分别模拟,比较设置前后的峰背比,验证理论分析的准确性.一类初级滤片模拟设置了Fe和Cu两种材料,结果表明设置后的峰背比较设置前的1.36均提高了两倍左右;二类初级滤片模拟设置了T e和Ba两种材料,设置后的最大峰背比分别为14.88和13.58,均比比设置前提高了10倍左右;平衡滤片则是先后设置Rh和Ru两个滤片,两者计数相减即得到平衡通带,结果可见通带内特征峰透过率为83.1％,而通带外的背景值降低到几乎为0,使得峰背比大大增加了.经过比较,三种滤片的设置都有效地提高了峰背比,其中平衡滤片提高的倍数最大,二类初级滤片次之,最小为一类初级滤片.理论上三种滤片是可以同时设置以更大地提高峰背比的,但由于轻基体中Cd元素含量很小,而低计数的结果会大大增加放射性统计涨落误差,因此,在实际应用中,还应考虑到这一点,以决定是否进行两两同时设置或者三者同时设置.研究创新之处在于除了传统的两种滤片外,还提出了二类初级滤片的运用.