Recent developments of the extemal beam facility of the Oxford Nuclear Microprobe
have led to an enhancement of the capabilities of the instrument for
analysing large or sensitive objects in air with a spatial resolution of 50 to 100
(xm. Used in conjunction with the 1 pm resolution in-vacuo facility this provides
a unique elemental analysis facility which is being applied to a number of archaeological
problems. This paper describes briefly the capabilities of the faci
lity and outlines the range of applications

Grime, G.W.

idUS. Depósito de Investigación Universidad de Sevilla

436I!; 'I ' : i| i'k/^aUPTMANM^9] Keesmann. I.. 1989, Chemischc und m • -tation eisenreicher Schiacken. In R p. nciailuntcrsucluiniien zur1987. Symposium Lihlice Í9H7. Praguc of ifO'^'Í20] Craddock,PT., 1995.£fír/v/V/ív«/A/,»,,,„ ,1211 r^i vrif n I - * " l*rn(im ti(>n. fuJinhuruh'■''i Gale, N.H., Papastamataki. A.. Stos-Gale y . " rce-and Copper Metallurgy in the Acgean Bro— ^ CoppCw Antiquity, fed. PT. Craddock and ""<1 Snwltinfi Technology81-101.^22] Levy, T., Adams, R.A. and Na|j„Hughcs). Brir. .Musi:um C)cc. 'Jordán: The Jaba! Hamrat Fidan (^krdí!TuHomepage. Arduu-nlo^y Projcc. 1999. Internet-Kólschbach,S., 1999. Expcrimcnic zur .Simni. . . . . ■y.i.-Verfahrenstechnik von Winddfcn. Priili'sK.rischer Kuprcrgcwinnung.Wissenschaften, Rhcin.-Westral. T-cchn M ""u «-''"ghau. Hiittenwesen und[241 D , "• ^'<»thschulc Aachcn.'  oachmann, H.G. and Rothcnbcrg. B.. 19x0 In^ri/cesFupfer/,n77nwa-ra/. (cds.H.G Conr von S-teheft J, Bochum, 215-236. ^ Rolhcnbcrg). Dcr Anschnitt. Be»-Hauptmann, A., Lutz, J., Pernicka. f£. yp.i v. 1 • , , -y derfriihesten Kupferverhüttung im Vordcrcn Oricnt ' í'"u ii Teclinolog»Mountains-Archaeologica Anatolica et M " ""iTn ver!ciío r o . r, / I tr '-^''poiarnica Alba Painiicn Dedicata UniverSita La Sapienza, Rom, ícd. M. Frangipane H w. \4 1 ;, 'tau - «M. Mellink^ 541-572. Hauptmann, M. I.i^crant, P. Mntlhiae &New ¡=™r' A . B^'^h-nann H.G, ttnd Maddin. R,. |yy„, c halcl.thic Cpper Smefing;AM r ?T h . Archnc.mciry (ej s. Demirci.Ozer and G.D. Summcr.s),Tubitak. Ankara 3 joHaup'^nn.A.andRoden.C.. '''««■ Archa«mciailurg¡sche Untcrsuchungcn zur Kupfcr-N.H., Bachmann, HG.. Rchenberg. B., Stns-Cútlc. Z.A. and Tylccttte R F.. 1990,ne Adventitiou.s Produclion of Iron in ihc .Smeliing al Coppcr. In Resmn hes in 'hn^abah 1959.1984. V„l. II.-The Aneen, Me,.,lu„.^, „, c- In.,-,. A,-cl,.,eo-McU,ll■ S'"'(ed. B. Rothenberg), London, 182-191 .Roilieriberg, B. and Shaw, C.T., 1990. The Discovery <,f a Oippor Mine and Sme"®''m Ihe End of Ihe Early Bronze Age (EB IV) in the Timna Vallcy. In.st. Archaeo-Me-• Studies, Newsletter 15/16, 1-8.^^"Ptmann. A., 1989, The Earlie.st Period.s of Copper Me.allurgy in Feinan/Jordan. I"« ^orld Archaeometallurgy, íed: A. Hauptmann. E Pernicka and G.A. Waener). C>er^nschn¡tt,Beiheft7 .Bochum, 119-135.[27][28][29][30][3l]p. VCU.y, I7/0, -y[32j Israel Explor. Soc., Jeru.salem.®=''-Arieh, I., 1983, Cenlral-Southem Sinai in the Early Bronze Age II and ,,, Reía^"■ran, R. (ed,), 1978, Earty Arad: The Chalc„u,hu Seniemen, and Early Bronze Age^"y- Israel Explor. Soc., Jerusale .^'•-Arie'dnship with Palestino. Levan! XV, .39-48.THE NEW EXTERNAL MICROBEAM FACILITYOF THE OXFORD NUCLEAR MICROPROBEAND ITS APPLICATION TO PROBLEMSIN ARCHAEOLOGICAL SCIENCEG.W. Grime*'^AbstractRecent developments of the extemal beam facility of the Oxford Nuclear Mi-croprobe have led to an enhancement of the capabilities of the instrument foranalysing large or sensitive objects in air with a spatial resolution of 50 to 100(xm. Used in conjunction with the 1 pm resolution in-vacuo facility this providesa unique elemental analysis facility which is being applied to a number of ar-chaeological problems. This paper describes briefly the capabilities of the facility and outlines the range of applications.1. INTRODUCTIONIon Beam Analysis (IBA) has a well-established role in the characterisation of ar-chaeological and historical objects. The combination of trace element sensitivity andquantitative accuracy offered by the techniques of Proton Induced X-ray Emission(PIXE) or Rutherford Backscattering (RBS) presents a solution to many problems in-volving the study of artefacts and raw materials. Using a suitable micro-focusing sys-tem, IBA can be carried out with a spatial resolution of the order of 1 pm [1], but thisis often inappropriate for archaeological objects. This is due to the nature of the materials, which are often heterogeneous, containing particulate inclusions with diametersof less than 100 micrometres. The long penetration depth of MeV light ions averagesthe signal over the range of the ions (tens of micrometres) and so unless thin samplesare used, it is not possible to analyse small inclusions separately from the matrix andthe advantage of using micron or sub-micron beams is lost. Another practical disad-vantage of high resolution microbeam facilities for archaeological applications is therequirement to place the sample in an evacuated chamber, which for most archaeo-University of Oxford. Deparlment of Materials. Parks Road. Oxford. OXl 3PH. UK438íi i ilüf11 !'<.1^1 NG.W.logical or historical objects requires sampling, which may be highiy undesirable forprecious, delicate objects.2. THE OXFORD EXTERNAD MICROBEAM FACILITYThe long range of MeV ions in air presents the possibility of analysing large orfragüe objects in air with no sampling required. The beam diameter is degraded bycollisions with air molecule (by approximately 10 pm per mm of air path), but as dis-cussed above, this is not a major problem for archaeological samples and by carefuldesign, a spatiai resolution of less than 50 pm can be achieved. For the majority ofsample ion beam analysis in air is non-destructive; the presence of air or helium aroundthe sample disperses any localised heating cause by the beam, and so prevents anythermal damage. In organic materials, decomposition of large organic molecules canIII Congreso Nacional de Arqueometría 439x-ray detector(light elements)Beamiine \(High vacuum)Partióle detector(below) Magneticdeflector;^^SampleExit nozzleGamma raydetectorabsorberx-ra/detector(trace eie/wddtsjj  .ihe V ^^hematic plan view of the external beam analysis facüity al Oxford. The beam emerges frotnQ  "^of the beamiine through a 300 pm diameter hale in a 2mm diameter copper nozzle sealedQf^ . ^  hm) plástic foil. X-rays emitted from the sample are detected by two detectors mounted aíray /• ^he beam. One detector isfitted with an x-ray ab.sorber to kiü the intense low energyhas ensure good detection limits for the trace elements while the other detectorthe °^^t)rber and is fitted with a magnetic deflector to ensure that high energy protons do not reachfor detector for gamma rays is mounted at 90" to the beam. Below the beamiine. a detectorple'^^^^'^'tS protons records the RBS spectrum and allows the total amount of charge falling on the sarn-^^mtored. Not shown in this diagram are a video microscope which uses a mirrar to view thesamni"'!'"^^ o/rte sample during analysis and a low power alignment láser to a.ssist in po.sitioning the^ for analysis.Figure 2. A general view of the newexternal beam facility being used forthe characterisation of surface layerson an IB"" century brome statue of Bud-dha.cause discoloration, but in many cases (e.g. papers) this fades over a period of daysand in any case is confíned to the small area of the beam.An external beam system has been developed for the Oxford Scanning Proton Micro-probe facility using design concepts described first by the AGLAE group in París [2](see figures 1 and 2). The key to high performance of this type of system is to mini-mise the distance between the exit of the beam from the vacuum and the sample. Thisreduces beam scattering and also reduces the absorption of the emitted signáis, but inorder to allow a free path from the sampling point to the detector. In this design theexit nozzle consists of a hollow copper cylinder with the diameter reducing in stepsfrom 12 mm to approximately 2 mm. Copper was chosen for the nozzle material inorder to reduce the gamma ray background which might result if light elements suchas Al were used and the beam strikes the inner surface. The only signáis induced fromcopper are the Cu x-rays, which do not escape from the walls of the nozzle. The beamemerges into air through a 300 (jim diameter aperture covered with an 8 (jim Kapton440(y \y. GRME III CoNGRi-so Nacional db Arqueombtría 441$,. r|lli i n'i : í' i I :1 ,Figure 3. Viewthrough the video"ticroscope of theexterna! beamfocility, This showsthe copper exitttozzle projectingfrom the bottomthe image and the^tirface of a sampieof J 8"" centuryislamic lustreware.Fhe outline of thelustre giazeddecoration can beseen as the darkregionsof the sampie.^indow. Two quadrupole lenses focus the beam through the no/.zlc, so that the amountbeam striking the aperture is minimised. Note that this aiso means that the spatial'"esolution is not determined by the size of the aperture holc. The sampie is mounted3pproximately 4 mm from the window, allowing a rcsolution of 40-50 pm to be^chieved on the sampie. Detectors for x-rays, recoiling protons and gamma rays allow®"3lysis using PIXE, RBS and also Proton índuced Gamma-ray Emission (PIGE) analy-for the detection of light elements such as Li and F. This allows virtually the en-Periodic tabie to be covered in a single measurement. A video microscope and aPower láser are used to align the desired región of the sampie in the beam (seagure 3). pyjj technical details of the new extemal beamiinc will be presentad alsa-where [3].^ separata development, the external beam facility has been fitted with a high^®^^sed pulsad láser to enable the surface of the sampie to be ablatad at axactlyspe ^Pot as the analysis is taking place (4). This exciting development is aimedrem^' corrosión layers on ancient metáis, but the ability todia ^"^3ce films in a well controlled manner over an area of less than 100 pmhave implications for many aspect of the analysis ot ancient materials,^  desirable to characterise separately both the corrosión film or patina and•^nderlying bulk material.3.^PPLICATIONS OF THE OXFORD EXTERNAL BEAM FACILITYTheteriai/- applications of the Oxford external beam to archaeological ma-summarised below:Panel t (fun) Hg%Top 5,08 11,30Top 5,08 11,60Centre 5,06 15,00Bottom 6,16 14,50Mean 5,35 13,10s.d. 0,54 1,923.1. CORROSION FILMS, SURFACE LAYERSAND BULK COMPOSITION OF METALSIn addition to using PIXE to characterise the composition of bulk metáis, thin(< 10 pm) surface layers can be characte-rised accurately and non-destructively usingRBS. This provides information comple-mentary to that which can be obtained forthick layers using the láser ablation facility. The Oxford extemal beam has been used to investígate a wide range of metal types,and alloys based on copper, silver, gold and iron have been investigated. In a study ofa medieval altar cross [3], the thickness and composition of the gilding layers was determined from the relative intensities of the gold, mercury and copper x-rays inducedby the beam. The ratio of the gold and mercury L-lines provided the Au:Hg ratio inthe amalgam gilded film, and since the copper x-rays from the substrate are absorbedby the overlying gilding layer, the ratio of the copper K-line to the gold L-line provides a very accurate measurement of the thickness of the film, as shown in table 1,in which presents the thickness and percentage of mercury recorded on the three backpanels.Another example, shown in figure 2, involved the investigation of a I?"* centuryBuddha from Thailand. Although this object was bronze, the black surface had an un-usual appearance. Using RBS, it was possible to determine that the surface was coatedwith a thin layer of organic material rich in carbón and oxygen which was diffusinginto the copper. One explanation for this could be the interaction of the metal with thesmoke of devotional lamps and candles over a long period.3.2. POTTERV AND GLAZESA major advantage of the extemal beam facility in the study of pottery is the ability to analyse the whole object without sampling, which can be difficult and undesiredon rare fragile objects. A range of analyses have been carried out both on whole ob-jects (e.g. the characterisation of blue and white glazes on Chínese porcelain) and onfragments (e.g. the analysis of IS"* century Islamic lustre glazes). In the case of thelustre glazes, the composition of the metal surface layer can be determined using PIXEand the thickness of the metal layer can also be determined using RBS. Figure 3 showsthe surface of a lustre giazed sherd viewed through the video microscope of the extemal beam facility. The copper beam exit nozzle can be seen at the bottom of thepicture and the decoration of the sampie can be seen. The dark regions are lustre giazed.Figure 4(a) shows the RBS spectmm acquired from the lustre giazed región using aprimary beam energy of 3 MeV. The small high energy peak in the spectmm indicatesthe metal lie copper layer resulting from the lustre glaze. The total area of this peak isa measure of the amount of copper present in the film, while the shape gives an in-dication of the depth distribution. In this case, although the statistics were not con-442 Q.W. Griue III Congreso Nacional de Arqueometría 443ÍH5 195 205 2i5 225 2^^ 2-3** 2^^ 275Kca.ojÍ^MeVr "f instreware ^ lazc rernrdcd in air nm/ií; proton.s \\ ir/¡ an iniíUil en^^'SyiiXCfl TÍ/fZ*^/ I í* (*/t y I li f u y/ í* y/y 1 f v yi»9y/ (/«•■• /■'>•.. «7... *í/ / S'/ //// i Iíi t ¡ í/// //V / // t? ^ ^'neasured data is shown as dots and thc thin ¡hu- is a thc(fretínprofiig , "'"•^"rea aai^ndthe appeurs as the snudl peak in thc hiith eners^'v re pión of thetrun¡ ig J Ofrom the glaze appear as steps at lower enerpy. The ¡arpe peak in the centre ofa bg recoils from nitropen and nxypen nuelei in the air. The dala nv/.v reeorded in 90^Pectr^ of JOOpA. (h): The iheoretiea! sample depth distrihution used to ealeidate the"^figure 4 (a).^lusfeasibility study, there is a strong indication of a diffusion profilein the glaze, as shown by the simuiated curves, resulting in the profile shown"gure 4(b).the3.3. *3lass and enamelbeajp ^ considerations of sampling aiso appiy to glass objects and the externalh3s also been applied to the characterisation not only of ancientjectjy í^rge fragments but also miniature mediaeval enamelled panels. Thc ob-such analyses has largely been to determine the nature of added constituents^olorants.Jewp,.■^LLERY and gemstonesThProvepa^ increasing interest in the analysis of ancient gemstones as an aidstudies [5 and 6]. Many gemstone minerals do not have a fixed comp^si-tion, and may comprise a mixture of end-members in varying concentrations. Exam-ples of these include gamets which have three end members and tourmalines with asmany as twelve. Determining the end-member fraction allows the comparison of stones(e.g. to determine whether all stones in an object were from the same source), whilethe trace element content may be characteristic of the mineral deposit, although thereis still a only a limited amount of comparison data available for this type of applica-tion. The extemal beam facility is ideal for the characterisation of mounted gemstones,since they do not have to be removed from the object in which they are mounted andthe technique is non-destructive. The Oxford facility has been used in a number offeasibility studies, including the characterisation for the fírst time of the tourmaline in-taglio of Alexander the Great from the Ashmolean Museum [7].4. CONCLUSION AND ACKNOWLEDGEMENTSThis brief description of the Oxford extemal beam facility has demonstrated the ca-pabilities of in-air micro-analysis using focused beams of MeV ions. This technique of-fers unique advantages to the archaeological scientist for the characterisation of ancientmaterials and artefacts, and a brief summary of applications has been presented. Thiswork has naturally involved the collaboration of co-workers from many different institu-tions, and the author especially wishes to acknowledge the contributions of the follow-ing people: Ms M.H. Abraham and Dr J.P Northover of the University of Oxford Depart-ment of Materials, Dr R. Camber of Sotheby's, London, Dr M. Vickers of the AshmoleanMuseum, Oxford, Prof. M. Tite of the Research Laboratory for Archaeology and theHistory of Art, Oxford and Dr L. Thoreson of the Getty Museum, Los Angeles.5. REFERENCES[11 Grime, G.W., Dawson, M., Marsh, M., McArthur, I.C. and Watt, F., 1991, The Oxfordsub-micron nuclear microscopy facility. Nucí. Instr. and Meths. B54, 52-63.[2] Calligaro, T, Macarthur, J.D., and Salomen, J., 1996, An improved experimental setupfor the simultaneous PIXE analysis of heavy-elements and light-elements with a 3 MeVproton extemal-beam. Nucí. Instr. and Meths. B109, 125-128.[3] Grime, G.W., Abraham, M.H., and Northover, J.P., The new extemal microbeam for theOxford Nuclear Microscopy facility, to be presented at the 7"' Intemational Conferenceon Nuclear Microbeam Technology and Applications, Bordeaux, September 2000, andpublished in Nucí. Instr. and Meths B, 2001.[41 Abraham, M.H., Grime, G.W., and Northover, J.P., The combination of extemal ion beamanalysis with controlled láser ablation for the study of thick corrosión films on ancientmetáis, to be presented at the 7"' Intemational Conference on Nuclear Microbeam Technology and Applications, Bordeaux, September 2000, and published in Nucí. Instr. andMeths B, 2001.[51 Querre, G., Bouquillon, A., Calligaro, T., Dubus, M., and Salomón, J., 1996, PIXE analysis of jewels from an Achaemenid tomb (4"'-century-BC), Nucí. Instr. and Meths. B109,686-689.444 G.W. Gk/aíe[6] Calligaro, T., Mossmann, A., Poirot, J.P., and Querré. G., 1998, Provenance study of rubíes from a Parthian statuette by PIXE analysis. Nucí. Instr. ami Mah.s . B138, 846-850.[6] Grime, G.W., and Thoresen. L.. Ion Beam Analysis of Gemstones - Investigation of aTourmalíne Intaglio of Alexander the Great in the Ashmolcan Museum. in Archaeogeni-mology, (ed. L. Thoresen), Getty Museum Publications. Los Angeles, (in prcss).THE DEVELOPMENT OF SPANISH METALLURGYAND COPPER CIRCULATIONIN PREHISTORIC SOUTHERN SPAINSophie Stos-Gale'"1. INTRODUCTIONThere is no doubt that in the Spanish Copper Age the earliest technological deve-lopments of copper smelting, and the extraction of silver and tin, were based on themineral resources of the Iberian Península. Much work has been conducted recentlyin Spain by scientists trying to link the trace elemental composition of prehistoric metalartefacts with the known ore sources, in particular a large amount of data on copperbased metáis and silver artefacts from all districts of Spain have been published recently by Rovira Llorens [1]. However, the archaeometallurgical survey of mineral resources, that needs to accompany such research, is largely limited to southem Spain,in particular the south west [2].In the eastem Mediterranean in the last twenty years there were several projectscombining archaeometallurgical surveys and chemical and lead isotope analyses of oresand Bronze Age artefacts [3 and 4]. The lead isotope compositions of ores and artefacts are used as their characteristic 'fmgerprints' [5], The analytical method used cur-rently for lead isotope characterisation of archaeological materials and ore minerals isThermal lonisation Mass Spectrometry (TIMS). This technique provides highly accu-rate data for lead isotope (LI) compositions of lead present in ancient metáis, glasses,glazes and pigments, even if lead is present only at the level of a few parts per mil-lion [6]. The LI provenance studies are based on the diversity of proportions of leadisotope atoms in ore minerals related to their geological history. This feature allowsto characterise geographical sources of minerals according to the pattem of the leadisotope ratios measured in them. The lead isotope characteristics of ores do not changeduring their smelting, carrying the LI fingerprint of the ore into the metal.The methodology of lead isotope provenance research is based on accumulatingisotopic, geochemical and archaeometallurgical information about known ore depositsoxIsotrace Laboratory of the Research Laboratory for Archaeology. University of Oxford. Keble Rd..^RH.

The new external microbeam facility of the Oxford nuclear microprobe and its application to problems in archaeological science

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The new external microbeam facility of the Oxford nuclear microprobe and its application to problems in archaeological science

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idUS. Depósito de Investigación Universidad de Sevilla