Ion Beam Analysis of Pigments
- PDF / 1,123,119 Bytes
- 8 Pages / 420.48 x 639 pts Page_size
- 62 Downloads / 220 Views
ION BEAM ANALYSIS OF PIGMENTS Barbara Cho,Joanna Baum,P. Revesz,W.S. Taft,D. Mayer,J.W. Mayor Cornell University, Dept. of Materials Science and Engineering Ithaca, NY 14853 ABSTRACT We have analyzed single and multiple layer paint samples to evaluate 3 MeV external beam proton induced X-ray emission (PIXE) for elemental analysis of inorganic pigments. The results are compared to those from energy dispersive electron microprobe analysis and Rutherford Backscattering Spectrometry (RBS). The advantage of PIXE is that the protons'penetration depth of 100 microns is more than 25 times greater than that of 20 keV electrons and 10 times greater than 3 MeV alpha particles, thus allowing analysis of relatively thick samples of up to 100 microns. The proton beam is passed into the atmosphere (external to the vacuum system) through a thin polymer film, and the beam area on target is 1 mmz. Electron microprobe and RBS require vacuum compatible samples; therefore, the pigments were painted on silicon wafers. Calibration was obtained from metallic thin-film samples of known thickness. The cross calibration of the three analytical techniques allowed evaluation of external PIXE analysis of paint films. We suggest that this nondestructive method is suitable for elemental analysis of drawings and paintings provided that further studies indicate no long term damage is caused.
3 MeV H __LJ Shieldin
X-rays
ubstrate
-X-ray detector Figure 1: Schematic of the external Proton Induced X-Ray Emission beam
Mat. Res. Soc. Symp. Proc. Vol. 185. , 1991 Materials Research Society
126
INTRODUCTION
In external beam PIXE, the proton beam is external to the vacuum and measures 1 mm in diameter. PIXE's main advantage is that the proton beam exits through a thin polymer film (kapton) outside of the beam line vacuum (Figure 1). Whole objects can be analyzed in ambient air similar to analysis by X-ray fluorescence (XRF).
For elemental analysis of inorganic pigments, X-rays, electrons, or ions create vacancies in the inner electron shell of the elements. Other inner-shell electrons make transitions to fill the vacancies and X-rays are emitted characteristic of the element. A technique utilizing this process, X-ray Fluorescence (XRF), is commonly found in museums.
Since its introduction in 1970, PIXE has been used for a wide variety of applications including a recent use in ink analysis. Thomas Cahill at the Crocker Nuclear Lab at the University of California, Davis, used PIXE to analyze the ink content and paper compotion of a Gutenburg Bible [1]. In addition, Robert Geoghegan of Cornell University recently analyzed a Robert Frost collection entitled Collected Poems to determine the elemental content of the ink, "Frost Black"; publishers had lost the recipe for this particular black ink
[2].
Analysis of thin paint layers at the Winterthur Museum in Wilmington, Delaware was conducted at Cornell by Debora Mayer using PIXE. Ms. Mayer analyze paintings by Charles Saint Memin dated between 1800-1808. Art historians were uncertain if the pink in
Data Loading...
