Laser induced breakdown spectroscopy tandem with laser ablation

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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.