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Advantage of Terahertz Radiation Versus X-Ray to Detect Hidden View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Archive Ouverte en Sciences de l'Information et de la Communication Advantage of terahertz radiation versus X-ray to detect hidden organic materials in sealed vessels Maryelle Bessou, Henri Duday, Jean-Pascal Caumes, Simon Salort, Bruno Chassagne, Alain Dautant, Anne Ziéglé, Emmanuel Abraham To cite this version: Maryelle Bessou, Henri Duday, Jean-Pascal Caumes, Simon Salort, Bruno Chassagne, et al.. Advan- tage of terahertz radiation versus X-ray to detect hidden organic materials in sealed vessels. Optics Communications, Elsevier, 2012, 285 (21-22), pp.4175-4179. 10.1016/j.optcom.2012.07.007. hal- 00731822 HAL Id: hal-00731822 https://hal.archives-ouvertes.fr/hal-00731822 Submitted on 13 Mar 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial - ShareAlike| 4.0 International License Advantage of terahertz radiation versus X-ray to detect hidden organic materials in sealed vessels Maryelle Bessou a, Henri Duday a, Jean-Pascal Caumes d, Simon Salort b, Bruno Chassagne b, Alain Dautant c, Anne Zie´gle´ d, Emmanuel Abraham e,n a Univ. Bordeaux, PACEA, UMR 5199, F-33400 Talence, France b ALPhANOV, 351 Cours de la Libe´ration, 33405 Talence, France c Univ. Bordeaux, IBGC, UMR 5095, F-33077 Bordeaux, France d Museum of Aquitaine, 20 Cours Pasteur, 33000 Bordeaux, France e Univ. Bordeaux, LOMA,UMR 5798, F-33400 Talence, France article info abstract Keywords: Terahertz imaging and conventional X ray have been used to investigate a sealed Ancient Egyptian jar Terahertz imaging preserved at the Museum of Aquitaine (France). Terahertz radiation revealed an unknown content that X-ray imaging could not have been visualized by X ray. By comparison with a model object, we concluded that this Organic materials content was composed of organic materials explaining their relative radiolucency. Art conservation Cultural heritage 1. Introduction region, has recently emerged as a possible powerful candidate in the field of art conservation for the investigation of various Art conservation science is a large expertise domain devoting art related materials [9]. Being non destructive and contact less in to the preservation and the protection of our cultural heritage. For nature, this wave can penetrate into non conductive and non polar the restorers, the scientific analysis of art materials provides materials and offer complementary spectroscopic data for a better information about the artist’s technique and artefacts history diagnosis and understanding of artworks. [1,2]. It also allows an accurate material selection for future In the field of art painting, THz imaging has already shown a restoration. For this purpose, various physical methods of diag great ability for the analysis of pigments [10 12] and preparation nosis are available. From UV to infrared, multi spectral imaging layers [13 16], the evaluation of mural paintings [17] or for the methods make it possible the examination of the artwork under character recognition in medieval manuscripts [18]. THz imaging different ranges of the electromagnetic spectrum [3 5]. Conven has been used for the analysis of Ancient Egyptian mummy [19], tional X ray is also considered as an efficient technique with sub written papyrus [20] and clay artefacts [21]. For dendrochronol millimeter spatial resolution. It provides highly contrasted images ogy applications, THz imaging was applied for tree ring analysis depending on the radiodensity of the materials [6,7]. However, [22,23]. In 2009, Adam et al. have compared THz imaging of the use of X ray is sometimes not recommended regarding to the painting with X ray and infrared reflectography [24]. They con ionizing power of the radiation and the difficulty of sample radio firmed that THz radiation can give information on the thickness of metric dating after X ray irradiation [8]. Radiography also requires hidden paint layers. They also observed that X rays do not easily strict safety rules based on the knowledge of the radiation effects penetrate layers of high density pigments, such as lead paint, and on the principles of protection. Only licensed users can mani which is ubiquitous in historical painting. More recently, Fuku pulate X ray producing devices and perform radiographic examina naga et al. reported the first use of THz time domain reflection tion, respecting safe operating procedures and ensuring the wearing imaging for the analysis of textiles of an Egyptian human mummy of personal dosimeters. Besides, an under exploited domain of the preserved at the Metropolitan Museum of Art (New York) [25]. electromagnetic spectrum, known as the terahertz (THz) spectral They pointed out the difficulty of conventional X ray to visualize the bandages due to the low radiological contrast of the fabric n layers. Except these two studies, to our knowledge, no other Corresponding author at: Univ. Bordeaux, LOMA, UMR 5798, F-33400 Talence, France. Tel.: þ33 540003122; fax: þ33 540006970. results have been published concerning the direct comparison E-mail address: [email protected] (E. Abraham). between THz and X ray imaging applied to art related materials. 1 2 In this paper, we propose to demonstrate the high potential of XVIIIth Dynasty (inventory number 8608). Its size is 97 mm in THz imaging for the analysis of ancient clay artefacts. Especially, height with a maximum diameter of 64 mm (Fig. 1(b)). Without we analyze a 3500 years old sealed clay jar from Ancient Egypt any specific decoration, it looks like a simple red clay vessel preserved at the Museum of Aquitaine (Bordeaux, France). In a hermetically sealed with a clay cork. A sticker under the object previous work, 3D tomographic imaging of the jar had been indicates that it was purchased in 1861 in Gournah, on the successfully performed using a specific reconstruction algorithm famous necropolis of Thebes (on the west bank of Luxor) [30]. [26,27]. In the present study, we provide an experimental evi The existence of the Menkheperre Tuthmosis III’s cartouche dence of the specificity of THz imaging compared to conventional (1479 1425 B.C.) on the jar clay cork allows to infer that this X ray in order to analyze the inner volume of the sealed artifact. important object was probably used during the pharaoh’s funer More generally, we establish that THz imaging is a well suited ary rituals. However, its real purpose still remains an opened and sustainable method for the detection of hidden materials question for the curators. contained in sealed vessels. 3. Results and discussion 2. Experimental methods and investigated material First, we investigated the transmission properties of earthen The experimental setup of the continuous wave THz imaging material at 110 GHz in order to quantify the amplitude of the system shortly called the ‘‘THz scanner’’ has already been transmitted signal as a function of the sample thickness. For this described [28]. Briefly, it consists of a compact millimeter wave purpose, we used terracotta from Salernes (Provence, France), a Gunn diode (110 GHz, 20 mW) coupled with a horn antenna red ferruginous clay purchased in a pottery shop. The greenware (Fig. 1(a)). The output beam is focused on the sample which is was shaped into parallelepiped slices of different thicknesses positioned on two axes XY motorized stages. At the sample from 4 to 33 mm, which were then fired in a kiln at 900 1C during position, the beam diameter is diffraction limited and the final 5 h. The inserted photograph in Fig. 2 presents the unglazed final image is obtained point by point by raster scanning the sample in bisques. For the measurements, the slices were simply positioned both horizontal and vertical directions. For the detection, we used into the THz scanner and illuminated by the 110 GHz radiation at a commercial low cost pyroelectric sensor (Spectrum Detector normal incidence. Inc.) and an optical chopper connected to a lock in amplifier. A 2D The absorbance at 110 GHz as a function of the sample thickness transmission image of the sample is obtained by moving the is shown in Fig. 2. The classical calculation Absorbance ¼ logðI0=IÞ object in the X and Y directions with a scan step of 2 mm in both has been used, where I0 is the transmitted signal measured without directions. With a scan speed of 5 pixels/s, the acquisition time for any sample and I is the transmitted signal measured in the presence a (100 Â 100) pixels image size is about 30 min. This portable THz of the sample. We can observe a linear increase of the absorbance scanner is well adapted for on site imaging since its volume is as a function of the sample thickness, which indicates that the about (500 Â 500 Â 500) mm3 with a total weight less than 20 kg. attenuation of the transmitted signal follows the Beer Lambert’s Moreover, as pointed out in the Introduction, the imaging system law. Assuming that the samples are made of homogeneous terra is easy to install and completely safe for the sample and the cotta, we can estimate the 110 GHz absorption coefficient a of the operator, unlike radiography. clay according to the expression Absorbance ¼ ad where d is the For standard radiography, we used a medical X ray tube sample thickness.
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