Marincan Pardede

Spectrochemical Analysis of Metal Elements Electrodeposited from Water Samples by Laser-Induced Shock Wave Plasma Spectroscopy

We have succeeded in applying laser-induced shockwave plasma spectroscopy (LISPS) to the problem of the detection and analysis of metal elements deposited from water samples by means of electrolysis. It is shown that metal elements are generally deposited in the form of a thin film on the electrode surface, while the electrode also conveniently serves as a subtarget for the relatively soft metal film, thereby providing the necessary conditions for the generation of shockwave plasma, which is favorable for highly sensitive spectrochemical analysis. It is shown that the detection sensitivity of this method reaches its highest value at low surrounding air pressure of around 1 torr. The lowest detection limit attained for various metal elements investigated in this experiment varies from around ten to a few tens of ppb. This limit can be readily improved upon by incorporating an optical multichannel analyzer into the detection system. We have thus presented a promising method for the realization of a compact mobile monitoring system for the accurate control of water and soil quality.

Characteristics of Hydrogen Emission in Laser Plasma Induced by Focusing Fundamental Q-sw YAG Laser on Solid Samples

Hydrogen emission has been studied in laser plasma by focusing a Nd-YAG laser (1,064 nm, 50 mJ, 8 ns) on various types of samples, such as copper plate, zinc plate and glass plate. Several parameters influencing the emission were varied, such as the type of gas (air, nitrogen and helium), gas pressures (ranging from 2 up to 760 Torr) and laser power density. It was found that Hα emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in the low-pressure region. It was also confirmed that the conventional well-known laser-induced breakdown spectroscopy (LIBS), which usually carried out at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. This specific characteristic of the pressure dependence of hydrogen is interpreted based on our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host elements.

Shock wave plasma induced by TEA CO2 laser bombardment on glass samples at high pressures

Abstract An experimental study has been carried out on the dynamical process taking place in laser plasma, generated by TEA CO2 laser (400 mJ, 100 ns) irradiation on glass samples surrounding by air of high pressures up to 760 torr. Accurate dynamical characterization was performed by simultaneous observation of the plasma emission front and the shock wave front. The shock wave front was detected by a modified shadowgraph technique while the emission front was detected by observing the rising time at various slit positions. In spite of the occurrence of a new feature uncommon to laser plasma, generated in low air pressures, it is found that the two fronts coincide and move together at the initial stage of the laser plasma, but eventually separate from each other, with the emission front being left behind the shock wave front at a later stage. These characteristics hold for the atomic emission lines of all elements contained in the glass samples examined, regardless of their different atomic weights. It is therefore strongly indicative of the shock wave mechanism in the laser plasma generation and the emission in the high-pressure surrounding air.

Hydrogen analysis in solid samples using laser-induced helium plasma at atmospheric pressure

A special technique for the modification of laser-induced breakdown spectroscopy (LIBS) has been developed to improve the spectral quality of hydrogen emission from a solid sample in helium gas at atmospheric pressure. In this technique, the plasma was generated by focusing a fundamental Nd-YAG (yttrium aluminum garnet) laser into a surrounding helium gas. The helium atoms excited to their metastable states would then serve to excite the atoms of the solid material vaporized by using another Nd-YAG laser. When properly synchronized, the resulting hydrogen emission line of H I 656.2 nm shows a dramatic improvement of the emission intensity and the spectral quality over what was obtained by conventional LIBS technique. This study further reveals that this improvement is mainly due to the role of the metastable excited state in a helium atom, which allows the delayed detection to be performed at a favorable moment when the charged particles responsible for the strong Stark broadening effect in the plasma hav...

Preliminary analysis of C and H in a Sangiran fossil using laser-induced plasma at reduced pressure

A Nd:YAG laser (1064nm, 120mJ, and 8ns) was focused on various types of fossil samples, including fossilized buffalo horns (around 400 000 and 1×106yr old, respectively) found in Sangiran, Indonesia. Such fossils represent an important starting point for tracing man’s origin and evolution during the Pleistocene era. Carbon emission was found to decrease significantly with the degree of fossilization and no carbon emission was found in a horn fossil dated at 1×106yr. Some molecular band spectra were also found in all the fossils examined in this study. It was assumed that by combining information on carbon emission, hydrogen emission, and molecular band spectra that the degree of fossilization might be quantitatively calculated. Further results showed that silicon emission is not detected in old fossils, but it is present as a major constituent. This is probably due to the fact that silicon is strongly bound to other elements in old fossils and is ablated in the form of clusters. In order to prove the abov...

Direct Observation of Developed Plastic Deformation and Its Application to Nondestructive Testing

A band pattern representing what we believe to be a developed, localized plastic deformation has been discovered in a fringe system formed by electronic speckle-pattern interferometry. Time historical tracing of this pattern enables us to predict the location and timing of material fracture before any other visible indication appears. Application of this observation to nondestructive testing is discussed.

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.

Neutral and Ionic Emission in Q-Switched Nd:YAG Laser-Induced Shock Wave Plasma

Excitation mechanisms for copper and zinc atoms as well as their ionic species in the Q-switched (Q-sw) Nd:YAG laser-induced shock wave plasma have been investigated with a time-gated optical multichannel analyzer (OMA) system for various experimental conditions. It is demonstrated that the shock excitation process is the main mechanism responsible for the emission spectra for laser energy ranging from 8 to 86 mJ and surrounding air pressure from 2 to 50 Torr. At air pressure below 2 Torr, collision-induced excitation appears to take over and becomes the operative mechanism. In all cases, the neutral emission dominates over the ionic emission, leading to a high signal-to-background ratio, which tends to decrease, however, at higher laser energy and air pressure.

The role of He in enhancing the intensity and lifetime of H and D emissions from laser-induced atmospheric-pressure plasma

A series of measurements have been performed on the time dependences of the intensities of helium, hydrogen, and deuterium emission lines from the corresponding laser-induced helium plasma at atmospheric pressure for two different He flow rates. The prolonged Hα and Hβ emissions along with their constant intensity ratio over a relatively extended period indicate the need to provide an alternative excitation mechanism other than the well-known thermal excitation process in a hot plasma. This additional excitation mechanism is also related to the metastable excited state of a He atom as indicated by the similar characteristics of the observed time dependence of the emission intensities. The enhanced intensity and lifetime of He emission at a high He flow rate was explained in terms of the collision-induced increase in the number of He atoms excited to above the 2 S10 metastable state, which was also responsible for the delayed excitation of H and D atoms via an energy transfer mechanism involving a Penning-...

Detection of deuterium and hydrogen using laser-induced helium gas plasma at atmospheric pressure

An experimental study on gas analysis by means of laser-induced breakdown spectroscopy was conducted using a Nd-yttrium aluminum garnet laser (1,064 nm, 120 mJ, 8 ns) and helium host gas at atmospheric pressure on a sample of mixed water (H2O) and heavy water (D2O) in vapor form. It was shown that completely resolved hydrogen (Hα) and deuterium (Dα) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that the helium metastable excited state plays an important role in the hydrogen excitation process.