A crucial safety measure to be strictly observed in the operation of heavy-water nuclear power plants is the mandatory regular inspection of the concentration of deuterium penetrated into the zircaloy fuel vessels. The existing standard method requires a tedious, destructive, and costly sample preparation process involving the removal of the remaining fuel in the vessel and melting away part of the zircaloy pipe. An alternative method of orthogonal dual-pulse laser-induced breakdown spectrometry (LIBS) is proposed by employing flowing atmospheric helium gas without the use of a sample chamber. The special setup of ps and ns laser systems, operated for the separate ablation of the sample target and the generation of helium gas plasma, respectively, with properly controlled relative timing, has succeeded in producing the desired sharp D I 656.10 nm emission line with effective suppression of the interfering H I 656.28 nm emission by operating the ps ablation laser at very low output energy of 26 mJ and 1 μs ahead of the helium plasma generation. Under this optimal experimental condition, a linear calibration line is attained with practically zero intercept and a 20 μg/g detection limit for D analysis of zircaloy sample while creating a crater only 10 μm in diameter. Therefore, this method promises its potential application for the practical, in situ, and virtually nondestructive quantitative microarea analysis of D, thereby supporting the more-efficient operation and maintenance of heavy-water nuclear power plants. Furthermore, it will also meet the anticipated needs of future nuclear fusion power plants, as well as other important fields of application in the foreseeable future.
An experimental study of double pulse LIBS is performed for the development of highly sensitive and quantitative analysis of Cl and Ca for the strength evaluation of concrete. The two lasers employed are arranged in orthogonal geometry and operated for delayed ablation with delay time of 10 μs, using He ambient gas at atmospheric pressure. The very large intensity enhancement is obtained over those detected with single pulse operation without generating the He plasma. It is most remarkable that the same sharpness and intensity enhancement observed in the previous double pulse experiment with 37 mJ laser ablation energy is achieved in the present experiment with much lower ablation energy of merely 2.5 mJ, resulting in average crater size of about 10 μm in diameter. Further, a linear relation is obtained between the Cl concentration and its emission intensity in alumina samples, while an estimated limit of detection of 80 ppm is obtained by using concrete sample, which is adequate for highly sensitive quantitative Cl analysis in concrete.
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