A Review of the Applications of Synchrotron Radiation in Archaeological Sciences

The scientific research regarding investigation, characterization and protection of the archeological specimens is manifested through a notable participation of multidisciplinary subjects and experts, scientists and archeometrists. One of the main principals which are considered by archaeometrists in the study of the precious specimens is the utilizing nondestructive methods. As an example, in synchrotrons, parameters such as the high photon flux, the small source size and the low divergence attained make it a very efficient source for a range of advanced spectroscopy and imaging techniques, adapted to the heterogeneity and great complexity of the materials under study. The use of synchrotron radiation techniques to study cultural heritage and archaeological materials has undergone a steep increase over the past 10–15 years. The techniques mainly have been focused on are: X-ray fluorescence (XRF), X-ray absorption (XAS), X-ray tomography microscopy (XTM), X-ray diffraction (XRD), and Fourier transform-infrared spectroscopy (FT-IR) analyses. Among these, XRF spectroscopy is based on the detection of characteristic X-rays emitted. Impinging X-rays on an atom creates inner electron vacancy in it, where the excited atom returns to its ground state, the fluorescing photon is emitted. The energy of this photon is the difference in energy between the vacancy and the electronic state of the electron filling the vacancy. Analysis of the XRF spectra includes identification of the elements from the fluorescence spectra observed. On the other hand, XAS (or X-ray Absorption Spectroscopy) relies on the absorption of X-rays by atoms of the materials in the vicinity of the absorption edge of one of its constituting elements. This technique gives chemical information on the coordination sphere of the absorber.  In X-ray tomography, a set of radiographs are taken and used to reconstruct a 3D morphology of the studied object. With two procedure, the obtained 3D morphology corresponds to what is measured in the radiography: X-ray absorption contrast where the image formed on the detector is described assuming an straight trajectory for each photon when the density of the transversed matter modulates its intensity on the detector; where the main effect of the matter is refraction and the absorption is negligible, X-ray phase contrast plays role while the photon direction changes as it travels inside the material. Diffraction takes place whenever the wavelength of the interacting wave is comparable with a length scale of a periodic structure. Therefore, the analysis of X-ray diffraction patterns gives information about the atomic and molecular structure of matter. For amorphous systems, however, the absence of an ordered structure limits outcomes of the XRD technique. Nevertheless, it gives significant information on average interatomic or intermolecular distances. Infrared spectroscopy is based on a transition in the vibrational state of the molecules when the incident photon is absorbed. The energy of this photon is a characteristic of the nature of each vibration, involving a single bond or chemical group in the molecule. In this research, how synchrotron radiation, identified with super brilliant and parallel micro x-rays, can be applied to characterize archeological specimens is presented, and then, some results by which the advantages of using the synchrotron radiation technique over the prior ones can be stressed, noticeably, will be reasoned.hich the advantages of using the synchrotron radiation technique over the prior ones can be stressed, noticeably, will be reasoned.