Application of External Ion Beam at ITN to Cultural Heritage. Applications. Victoria Corregidor, Instituto Tecnológico e Nuclear

Transcription

1 Application of External Ion Beam at ITN to Cultural Heritage. Applications Victoria Corregidor, Instituto Tecnológico e Nuclear IBER June - Coimbra 1

2 Outline The IBA techniques What is IBA? PIXE and PIGE RBS The External ion microbeam facility at ITN Why? Development Applications: Mercury Gilt Objects Glass Metals / coins Conclusions and Future IBER June - Coimbra 2

3 What is IBA? The IBA (Ion Beam Analysis) techniques is a set of analytical techniques used to study the composition/quality of samples in a non-destructive way, using a high energetic beam of accelerated particles. IBER June - Coimbra 3

4 What is IBA? Outline The accelerated beam induce in the sample the emission of secondary radiation or particles. There is a specific IBA technique to study each one: NRA (Nuclear Reaction Analysis) ERDA (Elastic Recoil Detection Analysis) RBS (Rutherford Backscattering Spectrometry) PIGE (Particle Induced Gamma Emission) PIXE (Particle Induced X-ray Emission) IBER June - Coimbra 4

5 IBA: PIXE and PIGE Outline Recording the X / gamma ray generated from the sample: - Multi-elemental - High sensitivity, even ppm - Relatively fast Contagens Fe Cu Au Ag - PIXE: Elements Z> 12, Mg - PIGE: Elements: low Z Canal Obtain element identification quantification no depth profile no information about compound Counts γ kev 23 Na(p,p'γ) 23 Na γ kev 40 K Channel IBER June - Coimbra 5

6 IBA: RBS Outline Recording the backscattered particles from the sample: - Multi-elemental - Medium sensitivity, - Elements Z> 1 (proton beam) - Relatively fast Si Obtain element identification quantification depth profile no compound information IBER June - Coimbra 6

7 IBA: RBS Outline The combination of 2 or more IBA techniques allow us to know: element identification quantification depth profile Non-destructive - low beam currents are used. Short time needed for analysis. Possibility of point or scan analysis. IBER June - Coimbra 7

8 IBA Outline PIXE RBS Detector Contagens Si S Fe As Contagens Li C O Si Beam y Map Pixel As Canal Si Max. Canal Fe x S Min C Contagens Contagens 300 C O 200 Si C 100 O 0 Si Canal Contagens 3000 Li O Si Canal Canal Dr. L. C. Alves IBER June - Coimbra 8

9 Microprobe Outline at ITN IBER June - Coimbra 9

10 Why External Beam? Outline Problems under vacuum conditions: Size of objects, sampling is needed Damage: Heating (thermal damage) Drying Charging (Breaking) Difficult sample handling/viewing IBER June - Coimbra 10

11 The External ion microbeam On behalf of the FCT project POCI/CTM/60685/2004, the existing in-vacuum microprobe set-up (1999) was modified. At this moment, the microprobe can be used either in vacuum or in atmospheric conditions. IBER June - Coimbra 11

12 The External ion microbeam Some aspects to be considered under these conditions: 1. Window 2. Air: absorption of low energy X rays and energy loss of backscattered particles. 3. Spatial resolution degradation 4. Energy straggling IBER June - Coimbra 12

13 The External ion microbeam 1. Window The exit nozzle has 2 pieces Si3N4 window in a Si frame 100 nm thick 1 mm 2 IBER June - Coimbra 13

14 The External ion microbeam 2. Air X-ray detector installed RBS detector installed Nylon chamber for He rich atmosphere IBER June - Coimbra 14

15 The External ion microbeam 3. Spatial resolution degradation 4. Energy straggling Keep distances as low as possible micro-lasers micro-camera IBER June - Coimbra 15

16 The External ion microbeam /2007 Testing X ray and gamma ray detectors 07/2008 First experiments (PIXE and PIGE) He-flow control IBER June - Coimbra 16

17 The External ion microbeam Chest CMAG X-ray detector 2.Micro-camera 3.Exit nozzle with a 100 nm thick Si3N4 4. RBS detector with He flux 5. Two lasers 3.2 mm IBER June - Coimbra 17

18 Applications Outline Vacuum - Energy: 2MeV -1 na - Resolution: 2 x 3 μm External - Energy: 1.9MeV -1 na - Resolution: 70 x 70 μm 60 x 60 μm (He) 53 μm 1 mm Cu grid: 2000 mesh Cu grid: 50 mesh IBER June - Coimbra 18

19 Applications IBER June - Coimbra 19

20 Applications Outline The external microbeam can be applied for multiple studies in Cultural Heritage. Examples: tapestries, Roman glasses, stained glasses, jewelry, ceramics, etc. IBER June - Coimbra 20

21 Applications: Gilt objects The objects belong to Casa-Museu Dr. Anastácio Gonçalves, Lisbon. Ciborium, CMAG 1180 Silver with partially gilded areas. Ostensorium, CMAG 1164 Lisbon, c Golden silver. Reliquary, CMAG 1194 Spain (?).Sec. XVI Golden silver IBER June - Coimbra 21

22 The gilding process Diderot and d Alembert Gild process: application of a gold coating onto the surface of a lower quality alloy to make an object look like cast gold, improving the corrosion resistance of the objects. Widely used since ancient times. In the twelfth century, the fire-gilding (also known as mercury-gilding) became widespread used. IBER June - Coimbra 22

23 The gilding process Diderot and d Alembert A mixture of 1 part of Au to 8 part of Hg is added into a crucible and then heated. - The metals form a silvery amalgam that is poured into a vessel of water. After that, it is squeezed through a fabric to remove the Hg excess. - The surface to be gilt is prepared with an acid solution (number 1) IBER June - Coimbra 23

24 The gilding process Diderot and d Alembert The amalgam is applied to the surface with a hard brush (number 2) and then put onto a hot charcoal fire (number 3). Time (few minutes) and temperature ( ºC) were crucial and usually judged by the goldsmith experience when the amalgam changes colour from grey to dull yellow. IBER June - Coimbra 24

25 The gilding process Diderot and d Alembert At this stage around 2/3 of mercury is volatized. - The object is burnished (number 4) to compress the porous structure until create a smooth and brilliant surface. IBER June - Coimbra 25

26 Applications: Gilt objects A representative X-ray spectrum Cu - Kα Cu - Kβ Hg - Lα Hg - Lβ Ag-Kα Different ratios Au-Hg can be observed for each object Intensity (a.u.) Ag-L Fe - Kα Zn - Kα Au - Lα Au - Lβ Au - Lγ Hg - Lγ Channel Ag (%) Au (%) Hg (%) Impurities Reliquary Cu, Ca, Fe, Pb, Zn Ostentorium Cu, Ca, Fe, Pb, Zn Ciborium Cu, Ca, Fe, Pb, Zn IBER June - Coimbra 26

27 Applications: Gilt objects The ostensorium comprises three parts attached by screws: The base and the stem have an average composition of 12% of Hg. The monstrance is made of Ag-Cu, with concentration of 92 % and 6.5% of Cu. The rays have a dull yellow appearance, made of an Ag-Au-Cu alloy with concentration of 87 %, 7% and 6%. IBER June - Coimbra 27

28 Applications: Gilt objects The Ciborium is made of silver with some gilt decorative motives. The silver parts have an average composition of 93.3 % of silver. Traces of Hg (0.1 2%) and Au ( %) can be found. IBER June - Coimbra 28

29 Applications: Gilt objects General Scan Ca Fe Cu Zn Ag Au Hg Pb wt% Point Analysis wt% thick. Ca Fe Cu Zn Ag Au Hg Pb ~ 1 μm ~1.5 μm IBER June - Coimbra 29

30 Applications: Glass There is a strong collaboration with Dr. Márcia Vilarigues, from the VICARTE department. - Stained glasses - Corrosion studies Convento de Cristo, Tomar, Portugal Mosteiro da Batalha, Portugal IBER June - Coimbra 30

31 Applications: Glass objects Christ Saint Michael Hand-made glass object from a private collection. ~25 cm Date? Original? - Iconography study (paints, coins comparison) Dra. M. Vilarigues, Universidade Nova de Lisboa (Private object) - Internal and external structure Radiography Ultraviolet light - Composition X ray Fluorescence Spectroscopy PIXE/PIGE IBER June - Coimbra 31

32 Applications: Glass objects - Glass composition main compounds: Silica (SiO2) Sodium oxide (Na2O) Calcium oxide (CaO) lower: Potassium oxide (K2O) Magnesium oxide (MgO) soda-lime-silicate glass Despite different colours of the glass, the composition is almost the same. Composition of the glass and the iconographic characteristics may point to a byzantine object produced during the 10th or 11th century. IBER June - Coimbra 32

33 Applications: Coins / Medals Current work at ITN: Medals and coins from Composition: - Ag and Cu as main components - From the trace elements: Intensity (a.u.) Ag-L Cl Fe - K Cu - Kα Cu - Kβ Zn - K Pb - Lα Au - Lβ Pb - Lβ Au - Lγ Pb - Lγ Zr - detector Ag-Kα Ag-Kβ provenance, date of manufacture deduced In 1850, thanks to the Parker process it was possible to separate from silver elements such as: Zn, Sn, Sb, Au, Pb, Bi Channel IBER June - Coimbra 33

34 Applications: Coins / Medals Current work at ITN: The surrounding environment changes the surface composition: AgCl Ag2S CuO etc XRD rupia_1903 Silver Copper Sulfide Chlorargyrite Digenite Copper Oxide Ag-K Cl Fe S angle PIXE scan IBER June - Coimbra 34

35 Final remarks - Future Outline Thanks to the external microprobe set-up, several kinds of objects can be characterized in a non-destructive way. It has been successfully applied to: tapestries, pigment identification, roman and stained glasses, metals In the future: Design an accurate way to obtain a constant He flow Development of a charge measurement IBER June - Coimbra 35

36 Researchers involved Outline Dr. L. C. Alves Dr. R.C. da Silva Ph-D P.A. Rodrigues Dr. N. Franco Dr. V. Corregidor Dr. M. Vilarigues Special thanks to: Dr. M.T. Marques Dr. J.A. Ribeiro IBER June - Coimbra 36

37 Obrigada Gracias Thanks IBER June - Coimbra 37