基于PGNAA-XRF联合方法的铅汞混合样品检测的研究

瞬发伽玛中子活化分析(PGNAA)技术用于溶液中重金属元素原位检测时，由于样品成分复杂，中子俘获截面较大的中子毒物(汞)元素，对截面较小的元素(铅)检测精度干扰很大，因此分析精度相对不高。为实现混合样品中多种重金属的高精度原位检测，提出了一种提高热中子俘获截面较低元素检出限的PGNAA-XRF联合检测方法，设计了一套联合检测混合样品中重金属元素的装置;使用MCNP软件，根据重金属元素的特征γ射线和特征X荧光的计数对样品的尺寸进行优化，得到较合适的样品尺寸高度和半径分别为33和16 cm;并模拟研究了Hg和Pb混合样品中的不同浓度(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，模拟结果表明该混合样品中，Hg和Pb元素的I_γ和I_X均与c_i成良好的线性关系，通过探测Pb的X荧光信息，克服混合样品中高低热中子俘获截面元素间的竞争问题，能显著的改善Pb的检出限，最后拟合给出了PGNAA-XRF联合检测方法的经验公式，计算得到该装置对Hg和Pb元素的检出限分别为3.89和4.80 mg·kg-1。

Study on Simultaneous Mercury and Lead Detection in Water Samples with PGNAA-XRF

Prompt gamma neutron activation analysis (PGNAA ) technology is used in heavy metals measurement .It is found that the detection accuracy of lead (Pb) is impacted heavily by mercury (Hg ) ,because of thermal neutron cross section of mercury is much bigger than lead .In this paper ,a new combined detection method was proposed to improve the lead measure‐ment accuracy in situ environmental water rejects analysis by PGNAA‐XRF .Thus ,a combined measurement facility was devel‐oped to analyze the mercury and lead in water simultaneously .The geometry of set‐up is determined by a series of simulations with the MCNP code to improve the detection efficiency of the prompt gamma‐ray intensity (Iγ) and characteristic X‐ray fluores‐cence intensity (IX ) of element .The ideal sample height and cavity are 33 and 16 cm ,respectively .The influence of the relation‐ship between Iγ ,IX and different concentration (ci ) of Hg and Pb was researched by MCNP calculations ,respectively .The sim‐ulation results showed that there were good linear relationships between Iγ , IX and ci ,respectively .The empirical formula of combined detection method was proposed based on the above calculations .The limits of detection for Hg and Pb with the com‐bined measurement instrument were 3.89 and 4.80 mg · kg -1 ,respectively .It is a significant increase in performance of the mercury and lead detection simultaneously .