X-ray fluorescence imaging system for fast mapping of pigment distributions in cultural heritage paintings

Abstract

Conventional X-ray fluorescence imaging technique uses a focused X-ray beam to scan through the sample and an X-ray detector with high energy resolution but no spatial resolution. The spatial resolution of the image is then determined by the size of the exciting beam, which can be obtained either from a synchrotron source or from an X-ray tube with a micro-capillary lens. Such a technique based on a pixel-by-pixel measurement is very slow and not suitable for imaging large area samples. The goal of this work is to develop a system capable of simultaneous imaging of large area samples by using a wide field uniform excitation X-ray beam and a position sensitive and energy dispersive detector. The development is driven by possible application of such a system to imaging of distributions of hidden pigments containing specific elements in cultural heritage paintings, which is of great interest for the cultural heritage research. The fluorescence radiation from the area of 10 × 10 cm2 is projected through a pinhole camera on the Gas Electron Multiplier detector of the same area. The detector is equipped with two sets of orthogonal readout strips. The strips are read out by the GEMROC Application Specific Integrated Circuits (ASIC)s, which deliver time and amplitude information for each hit. This ASIC architecture combined with a Field Programmable Gate Array (FPGA) based readout system allows us to reconstruct the position and the total energy of each detected photon for high count rates up to 5 × 106 cps. Energy resolution better than 20% FWHM for the 5.9 keV line and spatial resolution of 1 mm FWHM have been achieved for the prototype system. Although the energy resolution of the Gas Electron Multiplier (GEM) detector is, by principle, not competitive with that of specialised high energy resolution semiconductor detectors, it is sufficient for a number of applications. Compared to conventional micro-XRF techniques the developed system allows shortening of the measurement time by 2-3 orders of magnitude.

Discovering the material palette of the artist: a p‐XRF stratigraphic study of the Giotto panel ‘God the Father with Angels’

“…Beyond its own history, a work of art as a painting or a fresco can reveal details regarding its historical age such as the habits or the tastes of people, and, more important for scientists and art historians, information regarding the technique, and the creative process used by the painter. Discovering how painted works of art were realized or, eventually modified, can be done by gathering data about its structure and composition and, because a great deal of information can lie tens or hundreds of microns below the surface, the possibility of study artworks layer by layer is valuable for art research In this scenario, X‐ray fluorescence (XRF) results as the most diffused and powerful technique; it gives extremely useful results, also as a consequence of the development of new devices, more and more sensitive and reliable, mainly when coupled with other spectroscopic techniques . Thanks to the fact that XRF allows a non‐destructive and non‐invasive elemental analysis also in air, XRF makes the study of the stratigraphic distribution of elements feasible also for cultural heritage objects: samples that require damage avoiding as a key feature to perform experimental studies.…”

Elemental mapping of Portuguese ceramic pieces with a full-field XRF scanner based on a 2D-THCOBRA detector

“…They are characterised by the unlimited dynamic range, high rate capability (> 1 MHz/mm 2 ), high soft X-ray detection capability (< 1 keV), and large detection areas (> 10 × 10 cm 2 ), and have been successfully implemented in different EDXRFI spectrometers [14]. An XRF imaging system for pigment distribution mapping of large area cultural heritage samples was developed by Zielińska et al [15]. It relies on a triple GEM detector operating in a gas mixture of argon and carbon dioxide flowing through the detector chamber, and a 2D-readout system.…”

Application of Factorisation Methods to Analysis of Elemental Distribution Maps Acquired with a Full-Field XRF Imaging Spectrometer

“…An alternative technique called full-field imaging has been proposed recently, and several projects are under development [ 20 , 21 , 22 ]. The full-field imaging technique requires a position-sensitive and energy-dispersive X-ray detector.…”