Joseph Salomon

Development of an external beam nuclear microprobe on the Aglae facility of the Louvre museum

Abstract The external beam line of our facility has been recently equipped with the focusing system previously mounted on a classical nuclear microprobe. When using a 0.1 μm thick Si3N4 foil for the exit window and flowing helium on the sample under analysis, a beam spot as small as 10 μm is attainable at a distance of 3 mm from the window. Elemental micromapping is performed by mechanical scanning. An electronic device has been designed which allows XY scanning by moving the sample under the beam by steps down to 0.1 μm. Beam monitoring is carried out by means of the weak X-ray signal emitted by the exit foil and detected by a specially designed Si(Li) detector cooled by Peltier effect. The characteristics of external beams of protons and alpha particles are evaluated by means of resonance scanning and elemental mapping of a grid. An example of application is presented, dealing with elemental micro-mapping of inclusions in gemstones.

TRACE ELEMENT COMPOSITION OF ARCHAEOLOGICAL BONES AND POST-MORTEM ALTERATION IN THE BURIAL ENVIRONMENT

Abstract We have performed Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) analyses with an external proton millibeam on archaeological bones in order to determine possible alteration processes in their burial environment (dissolution, uptake and diffusion of foreign ions). The PIXE method enables us to quantify the post-mortem alteration by determining the concentration profile of several trace elements like Al, Si, S, Mn, Fe, Cu, Zn and Sr in transverse bone sections, while that of fluorine is inferred from PIGE analysis. Examples of concentration profiles of archaeological bone cross sections from the Seine river site in Paris, Bercy (4000 B.C.), are shown.

PIXE/PIGE characterisation of emeralds using an external micro-beam

Abstract A large collection of emeralds of various occurrences has been analysed by PIXE/PIGE in view to establish a compositional database. Major elements (Be, Si, Al) and trace elements (Li, F, Na, Mg, Ca, Rb, Cs and transition metals) are determined using an external 3 MeV proton micro-beam. Elemental micro-mapping permits to select the useful provenance tracers. This database was applied to infer the origin of several ancient emeralds set on historical jewels.

Alteration of lead silicate glasses due to leaching in heated acid solutions

Leaching processes were studied for lead glasses having a composition similar to that of certain archaeological materials (66 wt% PbO) to determine the mechanism of the structural evolution. The glasses were leached in two static acid media (HNO3 and CH3COOH, pH 2) at 90 °C for 35 days. Analyses were undertaken of the leaching solution (pH, inductive coupled plasma–atomic emission spectrometry) and of the bulk glass (scanning electron microscopy–energy dispersive X-ray spectrometry, Rutherford backscattering spectrometry, Raman). Results show that in both acids, up to 1 day a silicon-rich surface layer is formed via typical diffusion processes. This process continues up to 35 days in the case of acetic acid. In nitric acid, one observes a stabilisation of this layer and an increase in the metal content. In both cases, Raman data are used to interpret the structural evolutions which occur in the ‘gel’ phase.

The dedicated accelerator-based IBA facility AGLAE at the Louvre

Abstract The 6 SDH-2 2 MV tandem Pelletron accelerator of NEC has been installed at the Louvre to characterize museum artifacts by using IBA analytical techniques: PIXE and PIGME, RBS, ERD, as well as NRA. The facility is fitted with an electrostatic energy scanning system for automatically carried out resonance depth profiling. The accelerator hall has been designed to facilitate all the possible developments of AGLAE during the next decade, including a microbeam and AMS. The hall is entirely surrounded by one meter of concrete for the protection against deuteron-induced neutrons from d-RBS, NRA and DIXE-DIGME experiments. The machine is remote-controlled and will be entirely automated. Seven ports are available on the switching magnet. Two ports are already set up, one for IBA using a multipurpose vacuum chamber and the other for extracted-beam experiments. All the beam lines have been modularly designed for well controlled, halo-free beam impacts and a clean vacuum. We shall describe the facility and discuss the VME system for the automation of the experiments, the electronic equipment, and the powerful computer system used for the fast processing of the spectra, control of the experiments, and data storage.

An external milli-beam for archaeometric applications on the AGLAE IBA facility of the Louvre museum

Abstract External beam lines have been built on numerous IBA facilities for the analysis of works of art to avoid sampling and vacuum potentially detrimental to the integrity of such precious objects. On the other hand, growing interest lies on microprobe systems which provide a high lateral resolution but which usually work under vacuum. Until recently, the AGLAE facility was equipped with separate external beam and microprobe lines. The need of a better spatial resolution in the external beam mode has led us to combine them into a single system which exhibits numerous advantages and allows the analysis of small heterogeneities like inclusions in gemstones or tiny components of composite samples. The triplet of quadrupole lenses bought from Oxford is used to focus the beam. By using a 0.75 μm thick Al foil as the exit window, blowing a helium flow around the beam spot and reducing the window-sample distance below 3 mm, a beam size of about 30 μm can be reached. The experimental setup includes two Si(Li), a HPGe and a Si surface barrier detectors for the simultaneous implementation of PIXE, NRA and RBS. The full description of this device is given as well as a few applications to highlight its capability.

Ion beam analysis with external beams: Recent set-up improvements

Accelerator-based analytical techniques using external beams are ideally fitted to the study of works of art because of their fully non-destructive character. However, accurate quantitative analysis is not straightforward, due in particular to difficult beam monitoring. Significant improvements have been progressively made on the external beam line of the IBA facility of the Louvre museum in order to increase the accuracy and to conduct combined analyses with different IBA techniques.

Synchrotron X-ray micro-beam studies of ancient Egyptian make-up

Abstract Vases full of make-up are most often present in the burial furniture of Egyptian tombs dated from the pharaonic period. The powdered cosmetics made of isolated grains are analysed to identify their trace element signature. From this signature we identify the provenance of the mineral ingredients in the make-up and we observe different impurities in products, which have been demonstrated as synthetic substances by previous works. Focused X-ray micro-beam ( 2×5 μm 2 ) is successively tuned at 11 keV, below the LIII absorption edge of Pb, and 31.8 keV for global characterisation of the metal impurities. The fluorescence signal integrated over each single grain is detected against the X-ray micro-diffraction pattern collected in transmission with a bi-dimensional detector. Furthermore, for galena grains rich in Zn, the XANES signal at the K-absorption edge of Zn shows its immediate nearest-neighbour environment.

PIXE elemental mapping on original manuscripts with an external microbeam. Application to manuscripts damaged by iron-gall ink corrosion

Abstract Proton-induced X-ray emission (PIXE) mapping and PIXE spot analysis have been performed on three original manuscripts. We observed that the precision of the spot measurements for the analysis of the ink composition is limited by the heterogeneity of the writing. PIXE mapping proved to be a complementary technique which is much more sensitive, and which makes it possible to evaluate the migration of some elements, such as sulphur, iron and calcium around inscriptions.

Micro-PIXE analysis of an ancient Egyptian papyrus: Identification of pigments used for the “Book of the Dead”

Abstract This paper reports a study of colours and inks of an ancient Egyptian papyrus using an external proton microprobe in PIXE mode. Representing the Book of the Dead, this papyrus is dated from the 19th dynasty, New Kingdom (c.1295–1186 BC). Elemental maps were obtained by moving the papyrus under a fixed focused external beam using a motorised support. The maps were compared to photographic pictures taken in visible light. Inks used in the hieroglyph text appeared to be based on carbon (black) and iron oxide (red). Coloured drawings illustrating the text showed a wider palette: hematite, ochre, orpiment, Egyptian blue, verdigris. Most intriguing was the observation in several parts of the drawing of a whitish pigment containing strontium. Deposits of strontium-rich minerals (e.g. strontianite, celestite) have been identified in Egypt. The exact nature and the archaeological implications of this pigment have still to be determined. Finally, fine powder and coarse grains of arsenic oxide were observed, probably remaining from an early preservation treatment against insect attacks after excavation.