PGNAA-XRF联合检测水溶液中重金属的研究

重金属污染越来越受到人们的关注，迫切需要开发具有高精度的原位检测技术。瞬发伽玛中子活化分析（PGNAA）技术具有原位、无损、快速等优点而被广泛应用于重金属测量，但由于目前原位检测装置中使用的中子源通量相对较低，因此对一些重金属元素分析精度相对不高。为提高测量精度，直接利用PGNAA技术中的瞬发特征γ射线充当传统X荧光光谱分析的激发源，来激发重金属元素的特征X射线荧光（XRF）信息，提出了一种PGNAA-XRF联合检测水溶液中重金属元素的方法，并设计了一套由BGO和带铍窗的NaI组成的双探测器联合检测装置，分别用来探测PGNAA中瞬发特征γ射线和特征X荧光信息。通过MCNP分别模拟研究了Cr，Cd，Hg和Pb的浓度（ｃ_i）对瞬发特征γ射线强度（I_γ）和特征X荧光强度(I_X)的影响，模拟结果表明该装置中Cr，Cd，Hg和Pb元素的I_γ和I_X均与ｃ_i成良好的线性关系，并建立了联合检测方法的经验公式。比较重金属元素特征X射线荧光发现，该联合方法对Hg和Pb等高原子序数重金属的检测较灵敏，最后计算得到该装置对Hg和Pb等重金属元素的检测限分别为17.4和24.2 mg·kg-1。

New Methodology for Heavy Metals Measurement in Water Samples by PGNAA-XRF

In the present paper, a new combined detection method was proposed using prompt gamma neutron activation analysis (PGNAA) and characteristic X-ray fluorescence to improve the heavy metals measurement accuracy for in-situ environmental water rejects analysis by PGNAA technology. Especially, the characteristic X-ray fluorescence (XRF) of heavy metals is induced by prompt gamma-ray directly instead of the traditional excitation sources. Thus, a combined measurement facility with an 241Am-Be neutron source, a BGO detector and a NaI-Be detector was developed to analyze the pollutants in water. The two detectors were respectively used to record prompt gamma-ray and characteristic X-ray fluorescence of heavy metals. The prompt gamma-ray intensity (I_γ) and characteristic X-ray fluorescence intensity (I_X) was determined by MCNP calculations for different concentration (c_i) of chromium (Cr), cadmium (Cd), mercury (Hg) and lead (Pb), respectively. The simulation results showed that there was a good linear relationship between I_γ, I_X and (ｃ_i), respectively. The empirical formula of combined detection method was given based on the above calculations. It was found that the combined detection method was more sensitive for high atomic number heavy metals like Hg and Pb measurement than low atomic number like Cr and Cd by comparing and analyzing I_γ and I_X. The limits of detection for Hg and Pb by the combined measurement instrument were 17.4 and 24.2 mg·kg-1, respectively.