PORTABLE XRF ANALYSIS OF JAPANESE HISTORICAL OBJECTS

Transcription

1 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume PORTABLE XRF ANALYSIS OF JAPANESE HISTORICAL OBJECTS ABSTRACT Yasuhiro Hayakawa National Research Institute for Cultural Properties, Tokyo, Japan X-ray fluorescence spectrometry (XRF) is frequently used for the qualitative and quantitative analysis of the material of historical objects. However, there are many objects that have not been analyzed because they were immovable or could be damaged by transporting. In order to meet this problem, a portable XRF has been recently developed and enables elemental analysis for any object at any place. The instrument is based on energy dispersive XRF, and consists of a body approximately five-kilograms for X-ray irradiating, an electric power source, and a notebook PC for controlling and data acquisition. This newly developed portable XRF was applied for the non-destructive identification of the material of several Japanese historical objects. Some new information about the materials that have not been known was obtained. It was confirmed that portable XRF is a very useful tool for in-situ analysis of the material of historical objects. INTRODUCTION X-ray fluorescent spectrometry is widely applied for the qualitative and quantitative analysis in various fields because of its rapidity and non-destructiveness. This method has been used in the field of cultural artifacts for a long time and still today is the one analysis method used most frequently in performing composition analysis of historical objects [1,2]. In recent years, many new functions, including X-ray incidence capability at the order of m, elements distribution mapping function, and the ability to measure samples that exceed one meter in size, have been developed [3]. However analytical samples had to be brought to and placed in a sample chamber because most conventional instruments are large and immovable. In the field of cultural artifacts and historical properties the objects cannot be moved in many cases, and even if they can be moved, they may suffer some damage during transport or by changes in temperature and humidity. Besides there have been vigorous requests for a tool that can immediately analyze unearthed artifacts at the excavation site. In order to accomplish these demands, a portable fluorescent X-ray analyzer (XRF) has recently been developed that can do the elemental analysis at the site [4,5]. The newly developed portable XRF was applied for the non-destructive identification of the material of several Japanese historical objects including national treasures. In this paper, some new

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume information about the materials used in their objects is described. PORTABLE X-RAY FLUORESCENCE SPECTROMETER The portable XRF is based on energy dispersive XRF and consists of a measurement head of about 5kg for X-ray irradiation and detection, an electric power source, and a notebook PC for controlling and data acquisition. A rhodium X-ray tube (three-step switching voltage of 5, 15, and 50kV) and maximum current of 1mA was employed. The diameter of the X-ray beam was adjusted in the range of 2-10mm by a collimator. The analytical position can be observed by the CCD image, showing that the primary X-rays precisely irradiated the position wanted. In Table 1 a comparison is given between the portable EDXRF and a conventional EDXRF. between the portable and conventional EDXRF ANALYSIS OF IRON SWORD WITH GOLD INLAY INSCRIPTION The materials used for the characters on the Iron Sword with Gold Inlay Inscription, a Japanese national treasure, was analyzed by the portable XRF. This sword with the size of 73.5cm in length and 3.2cm in width was considered to be made in the 5th century. It was recognized as an extremely valuable object for understanding the ancient history of Japan, because of the 115 Chinese characters with gold-color inlay on both sides of front and back faces of the sword. In order to measure the chemical composition of the material of gold characters, more than 2 points for each of the 115 characters (57 on front and 58 on back faces) were examined non-destructively. The measurement setup is shown in Figure 1. The sword was put on a

4 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume wooden board placed below a 10 mm aluminum stand combined with the analyzer stand. The portable XRF was set at the center on top of the stand with the X-ray beam direction facing down. The X-ray beam was 2 mm in diameter and was set on 50kV, 0.1mA. Figure 1. Measurement setup for analyzing the Iron Sword with Gold Inlay Inscription Figure 2. Gold concentration for inscription on the Iron Sword with Gold Inlay Inscription

5 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume From the analysis, all the gold characters were made of gold-silver alloy. The concentration of gold and silver was calculated by theoretical fundamental parameter method after determining the detection efficiency for both elements. A content of gold for all measurement was shown in Figure 2. The following new information was obtained from the analysis: (1) Two kinds of Au-Ag alloy were used: one is Au70%-Ag30% used at the tip of front and back faces of the sword, and the other is Au90%-Ag10% used at the bottom of both faces. (2) The alloy of Au90%-Ag10% was used for the 35th to the 57th characters on the front face, and the 47th to the 58th characters on the back face. (3) More than 99% of Au content was found within three characters using the alloy of Au90%-Ag10%. It is difficult to explain why two kinds of materials were used, why the Au-Ag alloy was changed at different places between front face and back face, or why nearly pure Au was used only at three positions. We expect that these problems will be discussed based on the analytical data presented. ANALYSIS OF WOODEN SCULPTURE The polychrome materials on the surface of a wooden sculpture of Fugen Bosatu seated on an elephant, a Japanese national treasure made in the 12th century, were analyzed by the portable XRF. This sculpture, with a height of 114.4cm, was one of the most beautiful examples of a Buddha statue in wood. Fugen Bosatu seated on an elephant

6 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume Pedestal Bosatsu Clothes Fugen Bosatu seated on an elephant ANALYSIS OF GILDED WOODEN SCULPTURE A gilded wooden statue with a height of 65.7cm, made in the 7th century was also analyzed by the portable XRF. Pigments used and thickness of gold leaf on the surface were measured using gilded wooden statue

7 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume Figure 6 shows the relationship Ca-K intensity obtained and thickness of gold leaf calculated. As increasing thickness of the gold leaf, the intensity of Ca decreased, which means that a foundation layer containing Ca exists under the gilded. CONCLUSION Figure 6. Relationship between Ca-K intensity and thickness of gold leaf A portable X-ray fluorescent spectrometer that can be carried almost anywhere was recently developed, and was applied for the non-destructive analysis of several Japanese historical objects. Major and minor elements composing the objects could be detected safety and non-destructively. Some new information was obtained about important Japanese historical objects that have not been analyzed yet. The portable XRF is strongly expected to be an in-situ analytical method for investigating the material and polychromy of art objects. REFERENCES [1] J.L.Ferrero, C.Roldan, M.Ardid, E.Navarro, Nuclear Instruments and Methods in Physics Research, 1999,A422, 868 [2] M.Mantler, M.Screiner, F.Weber, R.Ebner, F.Mairinger, Adv. X-ray Anal.,1992, 35, 987 [3] Y.Hayakawa and Y.Hirao, Conservation Science, 37,137(1998) [4] K.Sugihara, K.Tamura, M.Satoh, Y.Hayakawa, Y.Hirao, S.Miura, H.Yotsutsuji, Y.Tokugawa, Adv. X-ray Anal.,2001, 44, 432 [5] Y.Hayakawa, S.Miura, T.Tsuda, Abstracts of the Pittsburgh Conference 2003, 2003, 459