Nasrullah Idris

Measurement of Concrete Strength Using the Emission Intensity Ratio between Ca(II) 396.8 nm and Ca(I) 422.6 nm in a Nd:YAG Laser-Induced Plasma

An experiment to investigate the potential of a laser-induced plasma method for determining concrete compressive strength was conducted by focusing a Nd:YAG laser on concrete samples with different degrees of compressive strength. This technique was developed in light of the role of the shock wave in the generation of a laser-induced plasma. It was found that the speed of the shock front depends on the hardness of the sample. It was also found that a positive relationship exists between the speed of the shock front and the ionization rate of the ablated atoms. Hence, the ratio of the intensity between the Ca(II) 396.8 nm and Ca(I) 422.6 nm emission lines detected from the laser-induced plasma can be used to examine the hardness of the material. In fact, it was observed that the ratio changes with respect to the change in the concrete compressive strength. The findings also show that the ratio increases with time after the cement is mixed with water.

New Technique for the Direct Analysis of Food Powders Confined in a Small Hole Using Transversely Excited Atmospheric CO2 Laser-Induced Gas Plasma

Taking advantage of the differences between the interactions of transversely excited atmospheric (TEA) CO2 lasers with metal and with organic powder, a new technique for the direct analysis of food powder samples has been developed. In this technique, the powder samples were placed into a small hole with a diameter of 2 mm and a depth of 3 mm and covered by a metal mesh. The TEA CO2 laser (1500 mJ, 200 ns) was focused on the powder sample surfaces, passing through the metal mesh, at atmospheric pressure in nitrogen gas. It is hypothesized that the small hole functions to confine the powder particles and suppresses the blowing-off of sample, while the metal mesh works as the source of electrons to initiate the strong gas breakdown plasma. The confined powder particles are then ablated by laser irradiation and the ablated particles move into the strong gas breakdown plasma region to be atomized and excited; this method cannot be applied for the case of Nd:YAG lasers because in such case the metal mesh itself was ablated by the laser irradiation. A quantitative analysis of a milk powder sample containing different concentrations of Ca was successfully demonstrated, resulting in a good linear calibration curve with high precision.

Hydrogen emission by Nd-YAG laser-induced shock wave plasma and its application to the quantitative analysis of zircalloy

An experiment was carried out to demonstrate the detection of a hydrogen emission line, HI656.2nm (Hα), in a plasma induced by a Q-switched Nd-YAG (YAG, yttrium aluminium garnet) laser in a low pressure gas on various types of samples, such as zinc, a glass slide, and a zircalloy tube. Contribution by surface water could be suppressed by a laser cleaning treatment and the resulting calibration curve obtained for zircalloy tube samples doped with various concentrations of hydrogen (0, 200, 540, and 960) suggest potential applications to the quantitative analysis of hydrogen. A study of the dynamic process represented by the time profiles of the hydrogen emission, in comparison with those for zinc atomic emission, revealed a specific feature that is related to the small mass of hydrogen. This specific feature can be explained by the shock wave excitation mechanism in terms of new hypothetical process, namely, a mismatch between the movement of ablated hydrogen atoms and the formation of the shock wave.

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.

Carbon analysis for inspecting carbonation of concrete using a TEA CO2 laser-induced plasma.

It has been demonstrated that a spectrochemical analysis of carbon using the laser plasma method can be successfully applied to inspect the carbonation of concrete by detecting carbon produced in aged concrete by a chemical reaction of Ca(OH)2 with CO2 gas in environmental air, turning into CaCO3, which induces degradation of the quality of building concrete. A comparative study has been made using a TEA CO2 laser (500–1000 mJ) and a Q-switched Nd– YAG laser (50–200 mJ) to search for the optimum conditions for carbon analysis, proving the advantage of the TEA CO2 laser for this purpose. Also, it was clarified that laser irradiation with suitable defocusing conditions is a crucial point for obtaining high sensitivity in the detection of carbon. Practical experiments on the inspection of carbonation were carried out using both a concrete sample that had been intentionally carbonated by exposure to high concentrations of CO2 gas and a naturally carbonated concrete sample. As a result, good coincidence was observed between the laser method and the ordinary method, which uses the chemical indicator phenolphthalein, implying that this laser technique is applicable as an in situ quantitative method of inspection for carbonation of concrete.

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...

Atomic Hydrogen Emission Induced by TEA CO2 Laser Bombardment on Solid Samples at Low Pressure and its Analytical Application

Hydrogen emission has been studied in laser plasmas by focusing a TEA CO2 laser (10.6 μm, 500 mJ, 200 ns) on various types of samples, such as glass, quartz, black plastic sheet, and oil on copper plate sub-target. 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. On the contrary, the conventional well-known laser-induced breakdown spectroscopy (LIBS), which is usually carried out at atmospheric air pressure, cannot be applied to the analysis of hydrogen as an impurity. By combining low-pressure laser-induced plasma spectroscopy with laser surface cleaning, a preliminary quantitative analysis was made on zircaloy pipe samples intentionally doped with hydrogen. As a result, a good linear relationship was obtained between Hα emission intensity and its concentration.

Hydrogen analysis of zircaloy tube used in nuclear power station using laser plasma technique

It is shown that remarkable improvements essential to a quantitative spectrochemical analysis of hydrogen emissions from the zircaloy samples were achieved when the low-pressure surrounding air used in the previous experiment of Nd-YAG laser-induced shockwave plasma was replaced by an inert gas. Using the high-purity (99.999%) nitrogen gas at 1.5 Torr, a linear calibration curve of the HI 656.2 nm emission line was obtained with a zero intercept from the zircaloy samples prepared with various hydrogen concentrations. Further, when the surrounding nitrogen gas was replaced by a helium gas, more than an order of magnitude enhancement was obtained on the signal-to-noise ratio, yielding a detection limit of less than 5 ppm.

Analysis of heavy metal pollution in soil using transversely excited atmospheric CO2 laser-induced plasma by trapping the soil in microstructured holes on metal subtargets.

A unique technique for direct analysis of soil samples utilizing a special advantage of a transversely excited atmospheric (TEA) CO2 laser-induced plasma generated at atmospheric pressure on a metal target has been developed. In this technique, a metal subtarget, such as nickel plate, structured with intentional microholes on its surface, each with dimensions of around 100 μm in diameter and depth, was used to selectively trap small sized soil particles by immersing the metal plate subtarget into the polluted soil sample. The trapped small soil particles on the metal subtarget were irradiated by a TEA CO2 laser (10.6 μm, 1.5 J, 200 ns) at atmospheric pressure under defocused condition with a spot size of 3 mm × 3 mm. This trapping and confining scheme substantially suppresses the blowing off effect; thus, the trapped soil particles can effectively be dissociated and atomized in the microstructured holes. Using this method of a microstructured metal plate subtarget, quantitative analysis was carried out on loam soil samples polluted by Pb. A linear calibration curve was obtained with a detection limit of approximately 50 mg/kg. Preliminary quantitative studies were carried out for a quartz sand sample containing Cr and Hg, resulting in linear calibration curves with detection limits of approximately 25 mg/kg and 10 mg/kg, respectively, at this stage. This technique is promising as a potential field screening tool for soil analysis.

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.