Analysis of sodium aerosol using transversely excited atmospheric CO 2 laser-induced gas plasma spectroscopy Ali Khumaeni a , Kazuyoshi Kurihara b , Zener Sukra Lie c , Kiichiro Kagawa d , Yong Inn Lee e, * a Research Group for Laser Probing, Japan Atomic Energy Agency, Nuclear Science and Engineering Directorate, Tokai-mura, Ibaraki-ken 311-1195, Japan b Department of Physics, Faculty of Education and Regional Studies, University of Fukui, Fukui 910-8507, Japan c Graduate School of Nuclear Power and Energy Safety Engineering, University of Fukui, Fukui 910-8597, Japan d Research Institute of Nuclear Engineering, University of Fukui, Fukui 910-8597, Japan e Department of Physics, Research Institute of Physics and Chemistry, Chonbuk National University, Chonju 561-756, Republic of Korea article info Article history: Received 10 August 2013 Received in revised form 13 December 2013 Accepted 18 December 2013 Available online 8 January 2014 Keywords: Analysis of sodium aerosol Laser-induced gas plasma spectroscopy (LIGPS) Pulsed TEA CO 2 laser Subtarget abstract Taking advantages of the special characteristics of a transversely excited atmospheric (TEA) CO 2 laser, the analysis of sodium aerosol has been successfully conducted by using laser-induced gas plasma spec- troscopy (LIGPS) method. In this study, the sodium aerosol was deposited on a nickel metal plate; the metal plate functions as a subtarget to initiate a gas plasma. When a pulsed TEA CO 2 laser was focused on the metal surface, a large-volume and high-temperature gas plasma was induced. The fine particles of sodium then entered into the gas plasma region to be dissociated and excited. By using this technique, a semi quantitative analysis of sodium aerosol was made. The detection limit of sodium was approximately 200 ppb. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Aerosol analysis is required in many important applications. For instance, in sodium-cooled fast reactors, radioactive sodium was found to contaminate the atmosphere around the reactors. The sodium leak is produced by vaporization or combustion of sodium, which could be released into the atmosphere from the cooling system piping or components. Because sodium aerosol is chemi- cally very reactive, it rapidly reacts with oxygen, water, and CO 2 in the atmosphere [1]. Therefore, highly sensitive method is really necessary to detect sodium leak in the atmosphere. Various kinds of sodium leak detector have been developed including sodium ionization detector and the ionization chamber, differential pressure detector, and contact leak detector [2]. How- ever, in those techniques, a sample preparation is necessary and they are labor intensive. Laser-induced plasma has become a very popular technique for qualitative and quantitative elemental analysis in aerosol samples [3]. In this method, a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with a pulsed energy of approximately several tens of milli-joules is focused in aerosol under atmospheric pressure of the surrounding gas. However, the sensitivity of this method is quite poor with limit of detection (LoD) of sodium of around 55 ppm [4]. On the other hand, we found that a transversely-excited atmo- spheric pressure (TEA) CO 2 laser is suitable for spectrochemical analysis. This is because the laser has long wavelength of 10.64 mm and long pulse duration of 200 ns. Based on our previous experi- ment, a high-temperature and large-volume gas plasma was induced when a TEA CO 2 laser was focused on a metal surface under atmospheric pressure of the surrounding gas, while the metal itself was never ablated; this phenomenon never occurs in the case of conventional LIBS technique, in which a Nd:YAG laser is most often employed as an energy source. This plasma is very favorable for spectrochemical analysis because its plasma temper- ature is rather high and it has a high heat capacity [5,6]. We have demonstrated that direct and rapid analysis of powder can be realized for TEA CO 2 laser-induced gas plasma method by employing a new technique, in which a powder sample was placed in a container and sent into the gas plasma region by the strong shock wave induced by the gas plasma [6]. While, for an ordinary LIBS method using YAG laser, powder samples must be prepared into a pellet prior to the analysis [7], thus the analysis is time consuming and requires additional equipments. * Corresponding author. E-mail address: lyong@chonbuk.ac.kr (Y.I. Lee). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cap.2013.12.017 Current Applied Physics 14 (2014) 451e454