Laser induced breakdown spectroscopy tandem with laser ablation

政府致力于提供可持续的低碳能源，这一战略目标需要跨学科的努力，以推进目前对放射性核素与地球材料（包括矿物、土壤和岩石）相互作用的理解。所产生的数据将用于监测和尽量减少放射性物质浸出对环境的影响，并预测其迁移速度。这可以建在放射性废物储存和地质处置的安全箱中。萨里大学目前的研究重点是放射性废物处理的安全性。特别是;（一）对天然含铀矿物进行表征，研究放射性废物的演变；(2)放射性核素与岩石、土壤相互作用机理；(3)天然有机物及其伴生污染物对放射性核素阻滞的影响。这项调查遇到的最大挑战之一是确定关键元素和放射性核素的迁移剖面及其与特定矿物相的关系。为此，串联LIBS-LA（激光诱导击穿光谱与激光烧蚀）将提供必要的元素范围，灵敏度和空间分辨率来支持这项研究。许多传统的分析技术只能提供大块材料中存在的元素的平均浓度，并且需要大量的样品制备，而其他技术可以获得有关某些元素的分布和特定相互作用的信息（元素测绘），例如XRF （x射线荧光）或EDX（能量色散x射线）。然而，由于它们的低灵敏度，它们只能应用于有限范围的元素。激光诱导击穿光谱法（LIBS）和激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）都是能够对固体样品进行元素制图并提供同位素信息的技术，且样品制备要求最低，它们是成熟的分析技术，有其独特的优点和缺点。在一个独特的仪器中结合这两种分析方法，正如这里提出的，是克服每种方法单独面临的挑战的一种非常有前途的方法。尽管LA-ICP-MS在灵敏度和分辨率方面取得了进步，但仍有某些元素和同位素无法测量。其中包括F， O， H和n。这是由于干扰，探测器的饱和（主要元素）和电离电位的问题（过高或过低）。另一方面，虽然LIBS可以成功地提供这些轻质和大块成分的定量和分布信息，但由于固体样品的物理和化学非均质性（矩阵效应）产生的时空变化，其精度受到限制。LIBS和LA可以结合使用，因为用于从固体样品中烧蚀小颗粒并带入ICP-MS的相同激光脉冲也可以产生激光诱导等离子体，可以通过光谱检测和分析。因此，LIBS和LA-ICP-MS的结合不仅扩大了可以同时测量的元素的覆盖范围，而且通过使用来自MS和光谱检测器的信号，采用多变量方法进行校准和信号处理，还将提高精度并减少光谱干扰。这个拟议中的英国独特的分析设施将有能力同时确定放射性核素与受意外泄漏污染的土壤、岩石和结构材料中的矿物和其他主要成分的分布和联系。这将提供有关放射性同位素进入环境的途径以及与自然介质相互作用机制的知识，以评估和尽量减少人类活动的影响。

The government is committed to deliver sustainable, low-carbon energy and this strategic goal requires a cross-disciplinary effort to advance the current understanding of the interaction of radionuclides with earth materials, including minerals, soils and rocks. The data generated will be employed to monitor and minimise the environmental impact from the leaching of radioactive materials, and to predict their migration rate. This could be built into the safety case for storage and geological disposal of radioactive waste.Current research at the University of Surrey focuses on the safety of radioactive waste disposal. In particular; (1) characterisation of natural uranium-bearing minerals to investigate the evolution of radioactive wastes; (2) mechanisms of interaction of radionuclides with rocks and soils; and (3) effect of natural organic matter and concomitant pollutants on the retardation of radionuclides. One of the biggest challenges encountered by this investigation is the determination of the migration profiles of key elements and radionuclides and their association to specific mineral phases. For this purpose, the tandem LIBS-LA (laser-induced breakdown spectroscopy with laser ablation) would offer the elemental range, sensitivity and spatial resolution necessary to support this research.Many conventional techniques of analysis only provide average concentration of the elements present in the bulk material and require intensive sample preparation, while others can obtain information on the distribution and specific interactions of some elements (elemental mapping), for example XRF (X-ray fluorescence) or EDX (energy-dispersive X-ray). However, due to their low sensitivity they can only be applied to a limited range of elements. Both laser-induced breakdown spectroscopy (LIBS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) are techniques that enable elemental mapping for solid sample and can provided isotopic information, with minimum sample preparation requirements, and they are well-established analytical techniques with their own unique advantages and disadvantages. The combination of the two analytical methods in one unique instrumentation, as proposed here, is a very promising way to overcome the challenges faced by each method individually.Despite the advances in sensitivity and resolution of LA-ICP-MS, there are certain elements and isotopes that still cannot be measured. These include among others F, O, H and N. This is due to interferences, saturation of the detector (for major elements) and problems with the ionisation potential (either too high or too low). On the other hand, while LIBS can successfully provide quantitative and distribution information of these light and bulk components, it suffers from precision limitations due to temporal and spatial variations generated by the physical and chemical heterogeneity of the solid samples (matrix effects). LIBS and LA can be combined, as the same laser pulse used to ablate small particles from the solid samples to be carried into the ICP-MS can also generate a laser- induced plasma that can be detected and analysed spectroscopically. Thus, the combination of LIBS and LA-ICP-MS not only expands the coverage of elements that can be measured simultaneously, but also it will lead to improved precision and reduction of spectral interferences by using the signals from both the MS and spectroscopy detectors applying a multivariate approach to calibration and signal processing.This proposed unique analytical facility in the UK will have the capability to determine simultaneously the distribution and association of radionuclides with mineral and other major components in soils, rocks and structural materials contaminated by accidental leaks. This will provide knowledge of the pathways of radioisotopes into the environment and mechanisms of interaction with the natural media, to evaluate and minimise the impact of human activities.