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- 3D-micro XRF (1)
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A new approach for chemical speciation in stratified systems using 3D Micro-XAFS spectroscopy is developed by combining 3D Micro X-ray Fluorescence Spectroscopy (3D Micro-XRF) and conventional X-ray Absorption Fine Structure Spectroscopy (XAFS). A prominent field of application is stratified materials within which depth-resolved chemical speciation is required. Measurements are collected in fluorescence mode which in general lead to distorted spectra due to absorption effects. Developing a reliable reconstruction algorithm for obtaining undistorted spectra for superficial and in-depth layers is proposed and validated. The developed algorithm calculates the attenuation coefficients of the analyte for the successive layers facilitating a new spectroscopic tool for three-dimensionally resolved nondestructive chemical speciation.
A combination of 3D micro X-ray fluorescence spectroscopy (3D micro-XRF) and micro-XRF was utilized for the investigation of a small collection of highly heterogeneous, partly degraded Dead Sea Scroll parchment samples from known excavation sites. The quantitative combination of the two techniques proves to be suitable for the identification of reliable marker elements which may be used for classification and provenance studies. With 3D micro-XRF, the three-dimensional nature, i.e. the depth-resolved elemental composition as well as density variations, of the samples was investigated and bromine could be identified as a suitable marker element. It is shown through a comparison of quantitative and semiquantitative values for the bromine content derived using both techniques that, for elements which are homogeneously distributed in the sample matrix, quantification with micro-XRF using a one-layer model is feasible. Thus, the possibility for routine provenance studies using portable micro-XRF instrumentation on a vast amount of samples, even on site, is obtained through this work.
A new fundamental parameter based calibration procedure for micro X-ray fluorescence spectrometers
(2011)
Fundamental parameter based quantification of X-ray fluorescence (XRF) measurement data requires an accurate knowledge of the spectrometer parameters, including the spectral distribution of the excitation radiation. In case of micro-XRF where a polycapillary optic is utilized in the excitation channel this distribution is changed due to the transmission properties of the lens. A new calibration procedure, based on fluorescence data of thin standard samples, was developed to determine the excitation spectrum, i.e., the product of the X-ray tube spectrum and the transmission of the used X-ray optic of a micro-XRF setup. The calibration result was validated by the quantitative analyses of certified multi-element reference standards and shows uncertainties in the order of 2% for main components, 10% for minor elements and 25% for trace elements. The influence of secondary order effects like Coster–Kronig transitions and cascade effects is analyzed and the accuracy of fundamental parameters in common databases is discussed.
In this work, the applicability of a new 3D micro X-ray fluorescence (3D Micro-XRF) laboratory spectrometer for the investigation of historical glass objects is demonstrated. The non-destructiveness of the technique and the possibility to measure three-dimensionally resolved fluorescence renders this technique into a suitable tool for the analysis of cultural heritage objects. Although absorption and resolution effects complicate qualitative analysis of the data, layered structures can be distinguished from homogeneous samples without the need for full quantification. Different manufacturing techniques were studied in this work with the help of hand-made reference samples. With the gained knowledge it could be shown for the investigated historical glass object, that black enamel as a stained glass contour colour was used in a cold painting. The object was not fired after the application of the black enamel, but instead the adhesion of the paint was solely provided through organic binding agents and the backing with metal foils. Thus, for the manufacturing of the object, a mixture of cold painting technique with a stained glass color was used. Quantitative measurements with a 3D Micro-XRF setup at the Berlin synchrotron BESSY II confirm the assumptions drawn on the basis of the qualitative investigation with the 3D Micro-XRF spectrometer with X-ray tube excitation.
3D Micro X-ray fluorescence analysis was used for the investigation of reverse-glass paintings. The material-specific combination used in reverse-glass paintings leads to damage phenomena reinforced by glass corrosion. To elucidate the mechanism of corrosion processes taking place in the glass object depth profiles of mobile elements are of interest. In order to obtain elemental depth profiles of such kind of fragile objects the method of choice should be non-destructive. Our first results demonstrate the usefulness of the 3D Micro-XRF measurements for this kind of investigations. The assumption that certain binding media may initiate corrosion processes beginning at the interface glass/binding material could be confirmed.
The Dead Sea Scrolls belong to the most important cultural assets of mankind. Their long term preservation and study is a challenge that demands an interdisciplinary approach. As early as the 1950s natural scientists assisted the scholars in studying the scrolls. It was at this time that the first extensive study of the scroll material took place. It was found that most fragments were written not on leather but on parchment. In addition, a method for determining the age of the parchment was developed which is still of value today. In the 1990s the AMS-C14 method confirmed the palaeographic determination of the age of the manuscripts. The use of carbon ink throughout the scrolls is also consistent with the known scribal practices of that time. There are, however, manuscripts, and among them the famous Genesis Apocryphon Scroll, which exhibit ink corrosion, normally associated with iron-gall inks.
Today, 60 years after their discovery, a community of scientists from the Jewish National and University Library (JNUL), the Technical University of Berlin (TU Berlin), the Federal Institute for Materials Research and Testing (BAM) and Fritz-Haber-Institute of the MPG (FHI) set out to scientifically investigate the finds of Qumran using the most modern methods. The results of the study will be used to determine the provenance of the texts as well as to contribute to their long-term preservation. A considerable part of the non-destructive investigation is taking place in the Berlin State Library and at the Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung , BESSY II.
Preliminary investigations, performed at the BAM on some fragments, were used to evaluate the extent to which X-ray analytical methods can provide information regarding the geographical origin of the fragments and match the individual pieces. The interpretation of the measurement results is made more difficult by age and storage of the objects. It is believed that ageing processes as well as conservation methods have altered the samples in addition to the changes caused by environmental influences.
In collaboration with the TU Berlin, the samples from the parchments found in the caves near Qumran were tested by means of three-dimensional synchrotron based X-ray fluorescence analysis (3D-SyXRF). The aim of this non-destructive investigation was the identification of the inorganic material used in the manufacture of the parchments.
The XRF experiments are supported by the non-destructive analysis by means of synchrotron based infrared spectroscopy (SyFTIR) in collaboration with BESSY II as well as optical and electron microscopy in collaboration with Fritz-Haber-Institute (FHI).