查看更多>>摘要：? 2021 Elsevier B.V.With ChemCam on NASA's Curiosity rover, SuperCam on NASA's Perseverance rover, and MarSCoDe on the Zhurong rover of the China National Space Administration, there are currently three instruments on Mars that employ laser-induced breakdown spectroscopy (LIBS) to analyze the chemical composition of Martian rocks and soils. With more than 880,000 LIBS measurements on Mars by ChemCam alone, the LIBS technique has been proven to be uniquely qualified for the in-situ robotic exploration of planetary surfaces. Since the laser-induced plasma exhibits a complex spatiotemporal evolution that has a significant impact on the recorded LIBS spectra, fundamental investigations of the plasma propagation and the spatial distributions of the plasma emissions can provide important insight that can help to improve the analysis of Martian LIBS spectra. Here we present first results from our LIBS plasma imaging setup, which allows us to spatially and temporally resolve the spectral emissions from the laser-induced plasma in simulated Martian atmospheric conditions. Investigating a calcium sulfate sample, we find that the commonly applied assumption of a nearly isothermal and homogeneous plasma with a colder outer layer is not sufficient to describe the laser-induced plasma on Mars. Instead, different spectral features show unique spatial distributions that suggest a strong influence of the outgoing shock wave. After plasma formation, the plasma center is found to rapidly become colder and more rarefied than the outer plasma regions. Molecular emissions are found to originate in this cold plasma center.
查看更多>>摘要：? 2021Monopropellant catalytic thrusters have been used for decades in space systems due to their simplicity and reliability. However, the degradation or loss of the catalyst is a major lifetime limiting effect, both for hydrazine fueled systems as well as for newer hydrazine-replacement fueled systems. Currently there is no in-situ diagnostic technique to measure the health status of the catalyst in such devices. Herein, we report a gas-phase diagnostic technique for measuring iridium, a common catalyst material for monopropellant thrusters. Laser induced breakdown spectroscopy was employed to quantify iridium in the gas phase by thermally vaporizing various organometallic iridium compounds to known concentrations within a test cell and observing the resulting iridium optical emission lines that had no interfering lines in the region from other possible emitting species (such as nitrogen, oxygen, and carbon). A limit of detection for the iridium was determined to be 6.21 μmol/L (197 ppm by volume), and this, to our knowledge, is the first report on the quantitative analysis of gas-phase iridium by laser induced breakdown spectroscopy.
查看更多>>摘要：? 2021 Elsevier B.V.The air particulate matter generated during welding operations is a major health concern for the welders as they trigger respiratory diseases. The information on elemental composition of the air particulate matter is required to know the toxicity as it depends on the constituent elements. We report the rapid analysis of air particulate matter at welding site, collected on whatman-41 filter paper. Internal standard method was used for the quantification of the elements both in energy dispersive X-ray fluorescence (EDXRF) and total reflection X-ray fluorescence (TXRF) spectrometry. In EDXRF, the sample was found to be thin for the elements Z > 29 and intermediate thickness for the elements 28 ≤ Z ≤ 19 and thick for elements of Z ≤ 17. About 17 elements were detected in air particulate matter and out of which Al, Si, Ca and Fe share the highest contribution. The composition of particulate matter is modulated by the composition of the welding material and the adjacent construction activities. The combined uncertainty in XRF was evaluated by identifying all the uncertainty sources. The study showed fast, non-destructive analysis capability of EDXRF and TXRF as an excellent micro-analytical technique for the air particulate samples.
查看更多>>摘要：? 2021 Elsevier B.V.Accurate uranium (U) composition analysis of the molten salt nuclear fuel mixture is a necessary step in nuclear fuel quality control. Laser-induced breakdown spectroscopy (LIBS) is an optical emission spectrometry technique for elemental composition. The non-linear phenomena in LIBS signal are the drawback of this technique, especially for high atomic number (Z) element in a complex matrix. To overcome this limitation, a hybrid chemometrics model of the partial least squares-artificial neural network (PLS-ANN) was used to quantify the U composition in the salt fuel mixture of Molten salt breeder reactor. This work shows the optimisation of several parameters, viz., spectra pre-treatment procedure, factor number of PLS for ANN input, number of hidden neurons and layers in ANN, activation function, and number of ANN iterations. The collective advantages of data dimension reduction from PLS and the nonlinear processing ability from ANN, improved the accuracy of LIBS quantitative analysis for U from ≈7% using simple PLS to ≈4% precision using a hybrid model.
查看更多>>摘要：? 2021 The AuthorsAnalytical methods based on dynamic-reaction cell (DRC) technology using ammonia as a reaction gas have been developed for the determination of ultra-trace Ti, Zn, Cu and Ag by inductively coupled plasma mass spectrometry (ICP-MS). Challenging spectral interferences from complex matrices were demonstrated to be overcome by DRC, and several DRC approaches (on-mass and mass-shift) using ammonium (NH3) as a reaction gas were assessed and compared to the standard or “vented” mode analysis. Ammonium cluster ions were generated for Ti, Cu, Zn, and Ag (mass shift approach). The on-mass approach was also explored to take advantage of collisional focusing phenomena. In addition, DRC operating conditions were optimised by modifying NH3 gas flow rate and rejection parameter q (RPq). The optimised conditions were applied to show the usefulness of either on-mass or mass-shift approaches when removing Ca and P interferences. Finally, the sensitivity of all measurement modes was studied and excellent limits of detection (at few ng L?1 levels) were assessed.
查看更多>>摘要：? 2021 Elsevier B.V.Energy dispersive photon spectrometry is a common analysis technique to quantify radionuclides present in a sample, the analysis is based on the knowledge of the photon emission intensities specific to each radionuclide. Among them, actinides have in general intense emission of L X-rays during the decay. However, their emission intensities are not well known and not detailed in the nuclear and atomic data tables due to the complexity of their spectra that cannot be resolved by conventional semiconductor spectrometers. Using a dedicated high energy resolution cryogenic detector, based on metallic magnetic calorimeter sensor technology, the L X-ray spectra of the decays of 238Pu(α) → 234U, 244Cm(α) → 240Pu, 237Np(α) → 233Pa and 233Pa(β?) → 233U were measured with an energy resolution between 23 eV and 43 eV (full width at half maximum) given access to an unprecedented level of detail. Moreover, the detector was conceived to provide a quasi-constant efficiency in the energy range of the L X-rays, minimizing the uncertainty for relative L X-ray emission intensities. Prior to the measurements, the full energy peak efficiency was carefully characterized, which enabled the determination of absolute emission intensities, with an uncertainty of the order of 1%. Some corrections had to be introduced using Monte Carlo simulations, in particular to take into account the surface activity inhomogeneities of the sources. Total and group L X-ray emission intensities are compared with the available data and with the recommended values. In addition, nearly 30 individual L X-ray intensities are presented.
查看更多>>摘要：? 2021 Elsevier B.V.In the present study, the direct current arc atomic emission spectrometry (dc arc AES) method was proposed for direct determination of chlorine impurities in nuclear-grade graphites and graphite foils in the range of 1-–100 ppm in order to meet nuclear power industry requirements. The procedure is based on near-infrared (NIR) AES approach for determination of non-metal impurities, contrary to the most common vacuum ultraviolet AES approach. Carbon dc arc in argon atmosphere was used as radiation source. This radiation source employs standard extra high purity 6 mm diameter standard shaped graphite electrodes and standard vertical spectroanalytic stand, but employs several improvements as well: special protective fused quartz tube, and specially built fiber optic refocuser. Registration of spectra was performed via a novel compact tunable spectrometer with linear complementary metal oxide semiconductor array (CMOS) detector. As the work in near-infrared spectral range is hampered by spectral interference factors, measures were taken to counter them. Due to specifics of the radiation source, the excitability of chlorine was studied both in air and argon in presence of carbon, as well as in its absence. Artificial standards for calibration of the spectrometer were prepared by mixing extra high purity NaCl and graphite powder and evaluated by two independent approaches: indirectly by dc arc AES determination of Na, and directly by water extraction and photometrical determination of Cl. The characteristics of evaporation and excitation in dc arc of chlorine from both standards and real nuclear graphite samples were studied due to the differences in the nature of chlorine source in them. The detection limit of was determined 0.8 μg/g. The whole cycle of measurement, including sample preparation is about 10 min.
查看更多>>摘要：? 2021 Elsevier B.V.The analytical potential of LIBS for the analysis of liquid solutions was evaluated using two experimental setups, one based on a TEA CO2 laser and the other in which Nd:YAG laser was used. Polytetrafluoroethylene (PTFE) was used as a substrate on which a 10 μL drop of analyte solutions with different concentrations of analyte elements, Be, Cr, Ni, Co, Pb, Tl, and V, were deposited and dried. The samples were deposited either directly on the PTFE or over the pre-deposited layer of copper oxide nanoparticles to study the influence of nanoparticles (NPs) on the ablation and plasma excitation. The obtained results imply that the presence of Cu oxide NPs does not significantly affect the analytical performance of LIBS based on TEA CO2 laser for analysis of solutions. At the same time, it was shown that plasma created by TEA CO2 laser radiation efficiently excited ablated material, making metal elements detectable in the sub-ppm concentration range. On the other hand, Cu oxide NPs significantly influence the formation and the analytical properties of plasma induced by Nd:YAG laser. Without the presence of NPs, the intensities of analyte lines were very low, unsuitable for spectrochemical analysis. At the optimal surface concentration of NPs, 0.36 mg/cm2, the intensity of analyte lines was increased more than ten times. Limits of detection of Be and Cr were 5.3 ppb and 33 ppb, with good linearity of curves of growth.
查看更多>>摘要：? 2021 The AuthorsSample or instrument vibrations can scatter laser impacts across the sample surface, which increases the uncertainty of laser-induced breakdown spectroscopy (LIBS) measurements. The common sources of noise associated to mechanical vibration are described and a method for isolating LIBS measurements from artifacts introduced by such fluctuations is presented. The approach circumvents the use of mechanical stabilizers by leveraging simple components common in LIBS systems. A camera was used to capture close-up images of the sample for each laser shot and the laser spot position in the sample surface was measured using common image processing techniques. By associating spectra with spatial coordinates in the sample surface, it was possible to reduce the relative standard deviation of the Cu(I) 427.51 nm signal in a patterned Cu/Al sample from 122.0% to 53.31%, similar to that measured for a pure Cu sample in the same vibration conditions. The spatial resolution of the method was found to depend on the laser spot diameter, the illuminance at the sample, the camera sensitivity and trigger insertion delay, and the speed of the laser beam sweeping the sample surface. The spatial resolution obtained with the setup used was ±0.6 mm at 15 m, i.e., 40 μm per meter of separation between the instrument and the sample with a vibration speed limit of 12 cm·s?1.
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