Spectral and dynamic characteristics of helium plasma emission and its effect on a laser-ablated target emission in a double-pulse laser-induced breakdown spectroscopy (LIBS) experiment.

A systematic study has been performed on the spectral characteristics of the full spectrum of He emission lines and their time-dependent behaviors measured from the He gas plasmas generated by a nanosecond neodymium-doped yttrium aluminum garnet laser. It is shown that among the major emission lines observed, the triplet He(I) 587.6 nm emission line stands out as the most prominent and long-lasting line, associated with de-excitation of the metastable triplet (S = 1) excited state (1s(1) 3d(1)). The role of this metastable excited state is manifested in the intensity enhancement and prolonged life time of the Cu emission with narrow full width half-maximum, as demonstrated in an orthogonal double-pulse experiment using a picosecond laser for the target ablation and a nanosecond laser for the prior generation of the ambient He gas plasma. These desirable emission features are in dire contrast to the characteristics of emission spectra observed with N2 ambient gas having no metastable excited state, which exhibit an initial Stark broadening effect and rapid intensity diminution typical to thermal shock wave-induced emission. The aforementioned He metastable excited state is therefore responsible for the demonstrated favorable features. The advantage of using He ambient gas in the double-pulse setup is further confirmed by the emission spectra measured from a variety of samples. The results of this study have thus shown the potential of extending the existing laser-induced breakdown spectroscopy application to high-sensitivity and high-resolution spectrochemical analysis of wide-ranging samples with minimal destructive effect on the sample surface.

Prostanoid EP1 receptor antagonist reduces blood-brain barrier leakage after cerebral ischemia.

Disruption of the blood-brain barrier (BBB) after cerebral ischemia is considered to be the initial step in the development of brain injuries, and an increase in the tyrosine phosphorylation of the tight junctional protein occludin has been shown to cause an increase in BBB permeability. Prostaglandin E2 (PGE2) appears to be associated with both toxic and protective effects on neuronal survival in vitro. However, it remains to be determined whether the prostanoid EP1 receptor is involved in the disruption of the BBB after cerebral ischemia. So we examined the effect of a prostanoid EP1 receptor antagonist, SC51089, on BBB leakage and tyrosine phosphorylation of occludin after cerebral ischemia. We demonstrated that SC51089 attenuated the increase in the tyrosine phosphorylation of occludin in isolated brain capillaries, which was coincident with a decrease in BBB leakage. These results suggest that the prostanoid EP1 receptor is involved in the tyrosine phosphorylation of occludin at tight junction, which may lead to disruption of the BBB and be linked to the development of cerebral infarctions.

Quantitative deuterium analysis of titanium samples in ultraviolet laser-induced low-pressure helium plasma.

An experimental study of ultraviolet (UV) laser-induced plasma spectroscopy (LIPS) on Ti samples with low-pressure surrounding He gas has been carried out to demonstrate its applicability to quantitative micro-analysis of deuterium impurities in titanium without the spectral interference from the ubiquitous surface water. This was achieved by adopting the optimal experimental condition ascertained in this study, which is specified by 5 mJ laser energy, 10 Torr helium pressure, and 1-50 mus measurement window, which resulted in consistent D emission enhancement and effective elimination of spectral interference from surface water. As a result, a linear calibration line exhibiting a zero intercept was obtained from Ti samples doped with various D impurity concentrations. An additional measurement also yielded a detection limit of about 40 ppm for D impurity, well below the acceptable threshold of damaging H concentration in Ti and its alloys. Each of these measurements was found to produce a crater size of only 25 mum in diameter, and they may therefore qualify as nondestructive measurements. The result of this study has therefore paved the way for conducting further experiments with hydrogen-doped Ti samples and the technical implementation of quantitative micro-analysis of detrimental hydrogen impurity in Ti metal and its alloys, which is the ultimate goal of this study.

Quantitative hydrogen analysis of zircaloy-4 in laser-induced breakdown spectroscopy with ambient helium gas.

This experiment was carried out to address the need for overcoming the difficulties encountered in hydrogen analysis by means of plasma emission spectroscopy in atmospheric ambient gas. The result of this study on zircaloy-4 samples from a nuclear power plant demonstrates the possibility of attaining a very sharp emission line from impure hydrogen with a very low background and practical elimination of spectral contamination of hydrogen emission arising from surface water and water vapor in atmospheric ambient gas. This was achieved by employing ultrapure ambient helium gas as well as the proper defocusing of the laser irradiation and a large number of repeated precleaning laser shots at the same spot of the sample surface. Further adjustment of the gating time has led to significant reduction of spectral width and improvement of detection sensitivity to ~50 ppm. Finally, a linear calibration curve was also obtained for the zircaloy-4 samples with zero intercept. These results demonstrate the feasibility of this technique for practical in situ and quantitative analysis of hydrogen impurity in zircaloy-4 tubes used in a light water nuclear power plant.

Quantitative hydrogen analysis of zircaloy-4 using low-pressure laser plasma technique.

It is found in this work that variation of laser power density in low-pressure plasma spectrochemical analysis of hydrogen affects sensitively the hydrogen emission intensity from the unwanted and yet ubiquitous presence of ambient water. A special experimental setup has been devised to allow the simple condition of focusing/defocusing the laser beam on the sample surface. When applied to zircaloy-4 samples prepared with various hydrogen impurity concentrations using low-pressure helium surrounding gas, good-quality hydrogen emission lines of very high signal to background ratios were obtained with high reproducibility under weakly focused or largely defocused laser irradiation. These measurements resulted in a linear calibration line with nonzero intercept representing the residual contribution from the recalcitrant water molecules. It was further shown that this can be evaluated and taken into account by means of the measured intensity ratio between the oxygen and zirconium emission lines. We have demonstrated the applicability of this experimental approach for quantitative determination of hydrogen impurity concentrations in the samples considered.