Thomas Calligaro

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.

Gold cultural heritage objects: a review of studies of provenance and manufacturing technologies

An overview of the use of the elemental composition of gold in the study of manufacturing technologies for objects as well as of the provenance of the metal is given. Depending on the objects, techniques based either on atomic physics or on nuclear physics and mass spectrometry are required to answer the questions surrounding the process of metalworking in the past. Several archaeological examples covering different periods of time and involving diverse analytical techniques are presented here. With those examples we illustrate the main research questions on precious objects and coins and show how far the elemental analysis of the objects can reveal the way they were made and provide information on the origin of the gold.

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.

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.

Combined external-beam PIXE and μ-Raman characterisation of garnets used in Merovingian jewellery

Abstract Red garnets were the dominant gemstones used for jewels in Europe during the Early Middle Ages. We have studied over 350 garnets set on 12 jewels unearthed in the royal necropolis of the Saint-Denis Basilica, close to Paris. This famous collection of “cloisonne” style artefacts dates from the Merovingian period (late fifth century AD to early seventh century AD). The archaeological issue addressed is the identification of the geographical origin of these garnets, in view to establish the gem trading routes during the Dark Ages. External beam PIXE was used to determine the major constituents (Mg, Al, Si, Ca, Mn, Fe), specifying the garnet type (composition in various mineralogical end-members, e.g. almandine, pyrope, spessartite, …), and the trace element content (Cr, Y). Three sorts of garnets were identified. Ten jewels are adorned with almandine garnets (Fe-rich). One jewel has intermediate almandine-pyrope garnets (“rhodolite”). The last and most recent jewel is inlaid with pyrope (Mg-rich) garnets. Trace element content and slight differences in major composition allowed to distinguish five different sources: two sources for pyrope garnets (with and without chromium), and two sources for almandine garnets (distinctive calcium, magnesium and yttrium contents). A preliminary comparison with literature data suggested that almandine garnets may have been mined from India while the “rhodolite” garnets may have been imported from Sri Lanka. The sources of pyrope garnets could be the Bohemian deposits (Czech republic). In addition, μ-Raman spectrometry was used to identify most of the mineral inclusions (apatite, zircon, ilmenite, monazite, calcite, quartz) present in almandine garnets. Even if two specific types of inclusions were not identified, due to the lack of corresponding reference spectra in our database, the Raman spectra collected provided an interesting inclusion fingerprint.

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.

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.