A PIXE mini-beam setup at the bonn cyclotron for archeometric metal analyses

The exact analysis of the elemental composition at and around a soldering joint of an antique piece of jewelry can elucidate the joining technologies and give hints of the genuineness of the object. As analytical method we use PIXE, which is nondestructive, multielemental and with fundamental parameter calculations gives absolute concentration values. To obtain the necessary spot size of the H₂⁺ beam at the Bonn cyclotron we use a piezo-controlled diaphragm, whose demagnified image is focussed on the target by two magnetic quadrupole triplets. With an electrostatic deflector the beam spot of 0.1 × 0.3 mm² size can be moved 2 mm in each direction on the target. With a laser beam, which simulates the ion beam, an irregularly shaped archeological object can be positioned. The laser is also used to obtain the alignment of the target surface to the ion beam direction and the small beam size makes it easier to find a flat part on the surface of the object; both of these are important preconditions for using the fundamental parameter method. A scan over a joint of modern gold alloys demonstrates the ability to detect soldering joints. The analysis of four pieces of Roman gold jewelry found in the area of Cologne and Bonn shows examples of brazing with a solder as well as diffusion soldering.     

Contribution from the experimental apparatus to the low energy background in Rutherford backscattering experiments

Low energy background was observed while bombarding a thin gold foil with protons. Measurements performed in different experimental arrangements and scattering calculations indicate that a large part of this background must arise from the pure energy definition of the bombarding beam. Particles of unknown origin and of lower energy than the nominal bombarding one were observed by which a separate energy spectrum of the low energy background of the Rutherford backscattering experiments was generated.     

Computer simulation of transmission sputtering of thin films and experimental measurements of recoil implantation of gold into silicon

Transmission sputtering of thin (up to 300 Å) gold films bombarded by 10 to 20 keV Ar ions is simulated by using the MARLOWE computer code. The energy spectra, angle of ejection and depth of origin distributions of ejected particles are presented. The results indicate that even for a thin film the cascading of the recoils is sufficient to produce an E^?2 energy spectrum and a cosine angular distribution. The evaluated transmission-sputtering yields for various film thicknesses are compared with the amount of gold retained in a silicon substrate in dynamic recoil mixing experiments.     

New directions in the Bartol PIXE system for studies in archaeometry

This paper describes, firstly, the physical processes of PIXE that underly its advantages as an analytical tool and the practical limitation met in the compositional patterning of ancient bronzes, irons and glasses. Controlled variation of the energy of the proton beam and the use of selective filters in the X-ray detection system allows certain background effects from the X-ray output of the dominant elements to be significantly reduced. Secondly, plans for a new beam line for the Bartol PIXE facility are described. This system will provide for a beam diameter as small as 20 μm with a laser-based optical system that will allow for the precise location of the proton beam on the artifact's surface. This system will enable one to study inhomogeneous materials, such as metal residues trapped in smelted slag, solder joints in classical jewelry and islands of metal in heavily corroded artifacts.     

Ion beam radiation effects in monazite

Monazite is a potential matrix for conditioning minor actinides arising from spent fuel reprocessing. The matrix behavior under irradiation must be investigated to ensure long-term containment performance. Monazite compounds were irradiated by gold and helium ions to simulate the consequences of alpha decay. This article describes the effects of such irradiation on the structural and macroscopic properties (density and hardness) of monazites LaPO₄ and La_0.73Ce_0.27PO₄. Irradiation by gold ions results in major changes in the material properties. At a damage level of 6.7 dpa, monazite exhibits volume expansion of about 8.1%, a 59% drop in hardness, and structure amorphization, although Raman spectroscopy analysis shows that the phosphate-oxygen bond is unaffected. Conversely, no change in the properties of these compounds was observed after He ion implantation. These results indicate that ballistic effects predominate in the studied dose range.     

Accumulation of decelerated gold ions

As part of our experiment to determine directly the mass of a gold atom in the SI unit kilogram, we have studied the interaction of decelerated gold ions with the surface of a gold coated quartz crystal. The ratio between the change of mass of the gold coated quartz crystal and the total charge of the ion current is measured as a function of the ion energy. The transition between the mass loss, mainly resulting from the sputtering effects, and the mass increase at the oscillator quartz, has been observed. At sufficiently low ion energies the measurements have shown a reasonable agreement with the expected value of the mass of a gold atom in the unit kilogram. Hence, the basic scheme for a direct determination of atomic masses in the SI unit kilogram has been successfully demonstrated.     

Compositional studies on Transylvanian gold nuggets: Advantages and limitations of PIXE-PIGE analysis

Minute fragments from nine gold nuggets from Transylvania - two belonging to placer deposits and seven to primary deposits - were analyzed by PIXE and PIGE at the AGLAE tandem accelerator of the Centre de Recherche et de Restauration des Musées de France (C2RMF) with a 3 MeV proton beam extracted into air. This study was triggered by some archaeological provenance issues for which the elemental characterization of the Transylvanian gold source, exploited from the Antiquity, was required. All analyzed Transylvanian gold nuggets are characterized by a consistently high amount of Ag (18% on average). Au and Ag add up to roughly 99%, the other elements - Cu, Fe, Te, Pb - being detected only at a trace level. The obtained results are in good agreement with the previous analyses of Transylvanian gold.     

Analysis of trace elements in gold alloys by SR-XRF at high energy at the BAMline

Measuring in a non-destructive way the characteristic trace elements of the metal allows following the circulation of gold in the past. The aim of this work is to probe the possibilities of X-ray fluorescence with high energy synchrotron radiation (SR-XRF) at the BAMline at BESSY II to determine the concentration of Pt in ancient gold alloys. A HP-Ge detector was used to measure the Pt K-lines excited with an incident energy of 79.5 keV. Data processing was done by subtraction of a Pt free gold standard spectrum from the spectrum of the sample. Depending on the sample composition, the MDL ranges between 40 and 90 ppm. The first results obtained for a small set of gold alloys of different thickness, size and composition showed that high energy SR-XRF is a significant method for the non-destructive determination of Pt in gold.     

Desorption of gold nanoclusters (2–150 nm) by 1 GeV Pb ions

Nanodispersed targets of gold (grains sized at 2–150 nm) were irradiated with 956 MeV ions of Pb⁵⁴⁺ ((dE/dx)_e in gold 87 keV/nm). Ejected gold was gathered on collectors. Desorbed nanoclusters of gold were detected by means of TEM while the total matter transfer was measured by neutron activation analysis. For all the targets a part of ejected gold presents nanoclusters in the same size range as that of the grains on the corresponding targets. Desorption of nanoclusters with the size up to 90 nm was observed for the first time for atomic primary ions in the electronic stopping regime. The yield of the desorbed nanoclusters decreases from 22 to 1.4 cluster/ion with increasing the mean grain size from 6 to 30 nm. The total matter transfer measured for the target with the grain size 6–10 nm has a great value – 5 × 10⁵ at./ion. Results are discussed.     

Seed Mediated Growth of Gold Nanoparticles Based on Liquid Arc Discharge

We report studies on the growth of gold nanoparticles by a seed-mediated approach in solution. The synthetic method is adapted from one we published earlier (Ashkarran et al. Appl. Phys. A 2009, 96, 423). The synthesized gold nanoparticles were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), UV-Vis spectroscopy, optical imaging and atomic force microscopy (AFM). Optical absorption spectroscopy of the prepared samples at 15 A arc current in HAuCl 4 solution shows a surface plasmon resonance around 520 nm. It is found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. The intensity of the plasmonic peak of the prepared gold nanoparticles for 1 minute arc duration gradually increases due to seed mediation for up to 6 hours. The formation time of gold nanoparticles at higher seed concentrations is less than that at lower seed concentrations.     

反应堆中子活化-多元素亚化学计量分离法测定生物和半导体材料中的Cu,Na,Au

近年来,由于Ge(Li)γ谱仪的普遍使用,亚化学计量分离法朝着多元素组分离的方向发展,亦可同时测定多种元素。 Elek和Kukala等人作了多元素亚化学计量组分离的理论研究,提出了关于MA_n类型的金属螯合物的多元素亚化学计量分离的关系式。如果指定:定量萃取(≥99％)金属离子M_i,同时保证亚化学计量(50％)萃取金属离子M_s,而金属离子M_1不被萃取,留在水相(≥99％);当等体积萃取时,有下述关系式:     

痕量金标样的超热中子活化分析

金矿是我国急需矿种。在以往找矿工作中,都是通过与金的伴生元素来找矿的,工作量大而收效低,近年来由于痕量金分析技术的进展,直接以痕量金异常来找矿,得到可喜的成绩。     

Synchrotron radiation X-ray fluorescence analysis on altered mineral muscovite in gold deposit

Synchrotron radiation X-ray fluorescence (SRXRF) microprobe was used to ananlyse altered mineral muscovite and its surrounding feldspar in Yuerya gold deposit. The major, minor and trace elements of the two minerals were detected and analyzed. SRXRF analysis showed that the Yuerya muscovite had a complex chemical composition. containing K, Fe, Ca, Ti, Cr, Mn, Co, Cu, Zn and many trace or ultra-trace elements. Since muscovite resulted from the alteration of hydrothermal ore fluid acting on feldspar (plagioclase), the difference of chemical composition between the two minerals shows the components of ore fluid, which are characterized by the enrichment of alkaline and alkaline-earth metal elements K, Ca and ore-associated elements Fe, Cu, Zn. And gold. silver and platinum, invisible under microscope, were detected in some areas of muscovite but not found in feldspar. Especially platinum, a mantle material is rarely seen in the earth crust but now found in the gold deposit of magmatic sources; its appearance approves the idea of mantle flux participating in the gold mineralization, which suggests that the tectonic event controlling gold mineralization in the Yuerya district is a mantle phenomenon.     

用X射线荧光探矿法在文裕金矿找金的研究

X射线荧光探矿技术是金矿资源勘查工作中的一种新的手段。选定砷、镍、铁作指示元素对文裕金矿岩样进行X射线荧光测定,测定结果表明:可以通过对金的最优指示元素受激后所产生的特征X射线荧光强度的测定来实现间接找金的目的;同时还可为地质填图、矿床成因与构造活动的研究提供资料。     

Formation of Au nanoparticles in sapphire by using Ar ion implantation and thermal annealing

In this paper, we present results of the synthesis of gold nanoclusters in sapphire, using Ar ion implantation and annealing in air. Unlike the conventional method of Au implantation followed by thermal annealing, Au was deposited on the surface of m- and a- cut sapphire single crystal samples including those pre-implanted with Ar ions. Au atoms were brought into the substrate by subsequent implantation of Ar ions to form Au nanoparticles. Samples were finally annealed stepwisely in air at temperatures ranging from 400 to 800 °C and then studied using UV-vis absorption spectrometry, transmission electron microscopy and Rutherford backscattered spectrometry. Evidence of the formation Au nanoparticles in the sapphire can be obtained from the characteristic surface plasmon resonance (SPR) absorption band in the optical absorption spectra or directly from the transmission electron microscopy. The results of optical absorption spectra indicate that the specimen orientations and pre-implantation also influence the size and the volume fraction of Au nanoparticles formed. Theoretical calculations using Maxwell-Garnett effective medium theory supply a good interpretation of the optical absorption results.     

Fingerprinting ancient gold with proton beams of different energies

The analytical techniques used in the field of cultural heritage are as far as possible non or almost non-invasive. Among them those based on proton beams show for gold fingerprinting, a good compromise between detection limits and destructiveness. The main characteristics of PIXE, PIGE, PIXE-XRF and proton activation analysis (PAA) are given for the study of gold alloys. Their main advantages and disadvantages are cited and their use in the field of archaeological sciences is illustrated by two historical examples. One example concerns the identification of the origin of the gold used in the decoration of the coffins from a Xiongnu necropolis (3rd c. BC to 2nd c. AD) found in present Mongolia. The other example establishes whether the coins attributed to the first king of Portugal, Alfonso I, were struck in the 12th century or in modern time.     

Desorption of gold nanoclusters (2-30 nm) under low excitation of their electronic subsystem by Ar ions (14 keV/nm)

Gold nanodispersed targets with islands-grains sized 2-30 nm were irradiated by Ar⁷⁺ ions with the energy of 45.5 MeV and (dE/dx)_e = 14.2 keV/nm in gold. The desorbed gold nanoclusters were studied by TEM method. For all the targets desorption of intact gold nanoclusters is observed. However, for inelastic stopping of monatomic Ar ions in gold of 14.2 keV/nm desorption of nanoclusters is observed only up to ∼25 nm. The yield of the desorbed nanoclusters considerably decreases from 3 to 0.02 cluster/ion with the increase of the mean size of the desorbed nanoclusters from 3 to 14.2 nm. The results are discussed.     

用于中子单色器镶嵌分布测量的γ衍射源设计

用γ衍射法测量中子单色器镶嵌角分布,要求γ入射束具有强度大、单能性好、发散度小等特点。为了满足上述要求,须对γ射线源(金材料)的形状和尺寸进行设计。本工作通过分析束流强度、束流发散度与束斑形状的关系,给出了金材料的矩形设计方案;通过蒙特卡罗计算,分析γ自吸收和γ康普顿散射在不同厚度下分别对束流密度和单能性的影响,给出矩形金材料在x、y、z3个方向的尺寸分别为0.6、6和10mm。用所设计的金材料制成γ源,成功实现了用γ衍射法对Ge单晶中子单色器镶嵌分布的测量。     

The secondary-electron yield measured for 5–24 MeV protons on aluminum-oxide and gold targets

The yield of first-surface secondary electrons from H⁺ impact on aluminum and gold targets is measured. Data are obtained for proton energies of 5 ≤ E ≤ 24 MeV on aluminum and 5 ≤ E ≤ 18 MeV on gold, and these data are compared with theoretical expectations and with previous data for lower proton energies. An empirical curve for the yield from aluminum-oxide is obtained from a theoretical curve for pure aluminum by using earlier measurements of primary-electron-produced yields from both aluminum and aluminum-oxide.