Gold,gildings, and tumbaga from the Moche tomb of the Lady of Cao: An EDXRF test for the internal ratio method

Gold, gilded copper, gilded silver, and tumbaga artifacts from the Moche tomb of the Lady of Cao, dated around 300 A.D., were analyzed by energy-dispersive X-ray fluorescence analysis. These artifacts are multilayered structures, which can be “reconstructed” using the K or L rays ratio of the chemical elements present in the layers. For example, in the case of gilded copper, the ratios Au (Lα/Lß), Cu (Kα/Kß), and Au-Lα/Cu-Kα, altered with respect to bulk gold or copper, can be used to determine the gilding thickness. An ideal test of this method was recently offered by the study of 15 big spears on gilded copper, a necklace composed of 12 small heads on tumbaga (a poor gold-alloy subject to depletion gilding), and a nose decoration on gilded silver. All these artifacts were found in (or close to) the tomb of the Lady of Cao, discovered 10 years ago in the north of Peru, close to Trujillo. The “internal ratio” method is described and discussed.     

A Roman bronze statuette with gilded silver mask from Sardinia: an EDXRF study

A Roman bronze statuette from the 2nd Century BC was recovered from a nuragic sanctuary close to Florinas, in the north of Sardinia. The facial portion of the statuette is covered by a silver mask, partially gilded and attached to the bronze by tin-lead welding. The silver mask was carefully analyzed by portable energy-dispersive X-ray fluorescence (EDXRF), a non-destructive and non-invasive method. The aim of the analysis was to reconstruct the layered structure of the silver gilt mask, and to determine homogeneity and thickness of the gold, silver and lead–tin sheets. This is possible by using the internal ratio of the X-ray lines, i.e. starting from the surface, Au (Lα/Lβ), Ag (Kα/Kβ), Au-Lα/Ag-Kα and Pb (Lα/Lβ).The results were compared with those obtained with simulated X-ray spectra, obtained both experimentally and by using the Monte Carlo simulation technique.     

Analysis of the spectacular gold and silver from the Moche tomb ‘Señora de Cao’

On the north coast of present‐day Peru, between the Andes and the Pacific Ocean, approximately between 100 and 600 ad , the Moche civilization prospered. The Moche were very sophisticated artisans and metal smiths, so that they are considered the finest producers of jewels and artifacts of the region. Their metalworking ability was impressively demonstrated by the excavations of the tomb of the ‘Lady of Cao’ (dated around third–fourth century ad ) discovered by Regulo Franco in 2005. Impressive is the beauty of the artifacts, and also the variety of metallurgical solutions, demonstrated by not only the presence of objects composed of gold and silver alloys but also of gilded copper, gilded silver, and tumbaga, a poor gold Cu‐Au alloy subject to depletion gilding. About 100 metal artifacts from the tomb of the Lady of Cao, never before analyzed, were studied by using various portable equipments based on following non‐destructive and non‐invasive methods:

• energy‐dispersive X‐ray fluorescence with completely portable equipments;
• transmission of monenergetic X‐rays;
• radiographic techniques; and
• optical microscopy.

Gold objects and gold areas of nose decorations are characterized by approximately the same composition, that is, Au = (79.5 ± 2.5) %, Ag = (16 ± 3) %, and Cu = (4.5 ± 1.5) %, while silver objects and silver areas of the same nose decorations show completely erratic results, and a systematic high gold concentration. Many gilded copper and tumbaga artifacts were identified and analyzed. Further, soldering gold–silver was specifically studied by radiographs. Additional measurements are needed, particularly because of the suspect that depletion gilding was systematically employed also in the case of some nose decorations. Copyright © 2016 John Wiley & Sons, Ltd.     

Thin thickness gilding determined by x-rays ratios from EDXRF-spectra

A by-product of energy-dispersive X-ray fluorescence (EDXRF)-analysis consists of using the ratios of selected X-ray peaks to determine the thickness of multilayered objects. Three different methods were developed in the past, all because the two main K or L X-lines from an EDXRF spectrum emitted by a chemical element have a distinct energy and are differently attenuated by an overlying layer. This specific subject has many papers dedicated, but only a few considerations were devoted to the limits of these methods, that is, the range, for example, of gold thickness that can be usefully determined by each method. This paper defines these limits in the specific case of thin gilding (with d < 1 μm). Three typical situations were considered, and the following artefacts were studied: two artefacts on gilded lead, where the gold leaf is superimposed to a white lead pigment, both in the painting “La Fornarina” of Raphael, dated 1520 AD, and in the imperial carriage of Dom Pedro II emperor of Brazil. In this last case, the white lead pigment was painted over the wood structure of the carriage; four artefacts on gilded copper, three crowns and a pendant, from the tomb of the Lady of Cao, from the Moche civilization of the North of Peru, dated around 350 AD; finally, an artefact on gilded silver, a vase from the Chavín civilization of the North of Peru, dated around 1000-200 BC.     

Total attenuation cross-sections of fluorescent X-rays of Zr,Sn, Ba,Au, Pb,Th and U in elements 6⩽Z⩽82

The total attenuation cross-sections in elements 6?Z?82 forK _α andK _β groups of lines of elements Zr, Sn and Ba andL _l ,L _α,L _β andL _γ groups of lines of the elements Au, Pb, Th and U have been measured. The experimentally measured attenuation cross-sections have been found in good agreement with the theoretical estimates.     

X-ray production by 1.5–11 MeV protons

K-shell ionization andL x-ray production cross-sections by proton impact have been determined from measurements ofK x-ray yields from thin targets of Ti, Fe, Co, Cu, Ni and Ag and ofL x-ray yields from Au and Pb. The proton energies varied from 1.5 to 11 MeV. A Si(Li) semiconductor detector recorded the x-rays. The total error in the measured cross-sections is mostly less than 5%.K _β /K _α ratios andL _l,β,γ /L _α ratios have been determined. Ionization cross-sections have been compared with predictions of the plane-wave Born approximation (PWBA) and the binary-encounter approximation (BEA). Both theories describe the ionization quite well: PWBA is, however, better for higher proton energies whereas BEA is superior for lower energies. An empirical formula for ionization cross-sections is derived.     

Alloying effects on Kβ/Kα intensity ratios and electrical properties in Cd1−xZnxS semi-conductor alloys

The alloying effect on K_β/K_α intensity ratio in Cd_1−xZn_xS semi-conductor alloys and on structural, electrical and optical properties of these alloys were investigated. The sample was excited by gamma rays with energy 59.5 keV photons from an Am-241 radioisotope source. K X-rays emitted by the sample were counted with a Si(Li) detector. We found that the K_β/K_α intensity ratio is changed by the alloying effect in Cd_1−xZn_xS semi-conductor alloys for different compositions x. We compared our results with the theoretical values.     

X-ray spectroscopic studies of electronic structure of the A15 compounds in the system Nb3(Sn-Al)

The present paper is concerned with the X-ray spectrum study of binary niobium A15 compounds and of solid solution based on these compounds. In the case of Nb₃Al the additional maximum of intensity in the long-wave length part of spectrum was observed. The results of the Al Kα-line shift and NbLβ₂-lines study lead to the conclusion that the valence electron Al to Nb₃Al, the decrease being still greater in the Nb₃(Al-Sn) alloys. The valence electrons of tin are largely localized on the “parent” atom.     

Study of the electronic structure of M(CO)5Cl complexes (M = Mn, Re) using X-ray spectroscopy and density-functional theory

The electronic structure of M(CO)₅Cl metal complexes (M = Mn, Re) has been investigated by X-ray emission spectroscopy. The obtained X-ray emission C Kα, OKα, Cl Kβ₁, MnLα, and MnKβ₅ spectra for Mn(CO)₅Cl and ReLβ₅ spectra for Re(CO)₅Cl have been interpreted on the basis of the quantum-mechanical calculations by the method of density-functional theory, using the Gaussian-98 program. The investigation of Mn(CO)₅Cl and Re(CO)₅Cl showed similarity of the electronic structure of both complexes. Only small differences have been revealed in the energy structure and orbital occupancies of the atomic orbitals of the corresponding molecular orbitals; these differences are caused by the difference of the type of metal ions and the molecule geometry. On the basis of the performed quantum-mechanical calculations, theoretical X-ray emission spectra have been constructed, which reproduce well the characteristic features of the corresponding experimental spectra of M(CO)₅Cl metal complexes (M = Mn, Re).     

Correlation between impurity binding energies and heat of formation of alloys

We survey recent hyperfine-interaction measurements of the binding energies E_B between two different impurities in dilute ternary alloys of iron, copper, silver and gold. The binding energies are related to the heat of formation of the corresponding alloys. A significant correlation between these two quantities is found.     

High-resolution X-ray emission Lα1 and Lβ2 Spectra of Hf, Ta, W, Re, and Os

The shape and relative intensities S _α=I(α_1s )/I(α_1s ), S _β=I(β_1s )/I(β₂) of the short-wavelength X-ray Lα₁ and Lβ₂ satellites arising from the radiative decay of the states corresponding to L ₃ M _4,5 configurations were investigated experimentally for Hf, Ta, W, Re, and Os. It was established that, in the case of W, the values S _α=2.5%, S _β=4.2% are five to seven times larger than those for Hf and Ta, and by (30–60)% smaller than those for Re and Os. On the basis of the obtained values of S _α,S _β, as well as the observed two-component structure of the Lα₁ and Lβ₂ satellites, it is concluded that the Coster-Kronig L ₁-L ₃ M ₅ transitions (CK) are allowed by the energy conservation law even for tungsten, and, starting with this element, they represent a major channel of generation of the states of LL ₃ M ₅ configuration. Possible features of such a process for the W atom are discussed in comparison with those for Re and Os.     

Determination of gold and silver in dross using EDXRF technique

Gold and silver in dross were determined by energy‐dispersive X‐ray fluorescence technique. Sample was prepared by pressed pellet method using microcrystalline cellulose powder as binder, and a method of standard additions was used for quantification. L_β X‐ray of gold (11.4 keV) and K_β X‐ray of silver (24.9 keV) were used for analysis. The measured concentrations of gold and silver were 132 ± 8 and 1181 ± 84 mg kg^?1, respectively. The results were validated by instrumental neutron activation analysis technique. The t‐test indicated that there was no significant difference between results obtained by the two techniques. Energy‐dispersive X‐ray fluorescence is a simple, precise and accurate technique for the determination of gold and silver in dross. Copyright © 2014 John Wiley & Sons, Ltd.     

Temperature dependence of the interband absorption edge of copper

The optical absorption spectra of bulk copper measured by Pells and Shiga have been fitted by means of a model calculation in the interband edge region. The optical gap and the dipole matrix element of the L₃-L'₂(E_F) transition have been determined as a function of the temperature and a comparison with similar results obtained for silver and gold is presented.     

Oxygen inducedK-shell ionization of selected elements from sulphur to bromine

K-shell X-ray production cross sections for oxygen ions on thin solid targets of 13 selected elements with atomic numbers between 16 and 35 were measured by a Si(Li) detector at incident ion energies from 7 to 24 MeV. Ionization cross sections are compared with calculations assuming Coulomb-ionization. Best agreement is found with theoretical cross sections that include corrections for binding energy and Coulomb deflection effects. Energy shifts ofK _α andK _β X-rays andK _α /K _β intensity ratios were also measured and are used to deduce information about outer shell ionization.     

Atacamite as a natural pigment in a South American colonial polychrome sculpture from the late XVI century

The image of Our Lady of Copacabana is a gilded polychrome sculpture manufactured in maguey wood at the end of the 16th century. It is a highly devotional image in the Andean region and her sanctuary lays at the shores of the Titicaca Lake in Bolivia. In this study, a green sample taken from the Virgin's veil has been analyzed with the aim to identify the green pigment and the gilding technique. The green pigment layer covered completely the shiny color of the gilded area. First, the cross section of the sample was examined by optical microscopy revealing the presence of green crystals on a white layer; beneath it, a gold leaf on a red bole was observed. Scanning electron microscopy‐energy dispersive spectroscopy analysis allowed the identification and quantification of copper and chloride in the green pigment layer. Analysis by micro‐Raman spectroscopy indicated the presence of atacamite (Cu₃Cl₂(OH)₃) as the green pigment. Although this compound has been identified as a degradation product of copper pigments or of metallic objects containing copper, in this polychrome sculpture, atacamite was used as the green pigment and is identified for the first time as a mineral pigment in a colonial sculpture made in the Viceroyalty of Peru. Copyright © 2012 John Wiley & Sons, Ltd.     

Relativistic calculation of atomic X-ray transition rates

The fully relativistic transition probabilities in atomic X-ray emission are calculated for a wide range of selected elements of the periodic table, fromZ=21 toZ=93. The treatment includes the effect of the retardation of the radiation field. The atomic model used is the self-consistent relativistic Hartree-Fock, with the Slater approximation for the exchange term. The formulas for EL and ML multipole transition rates are derived, and transition rates are calculated for all transitions to theK-shell,L-subshells, andM-subshells. The contributions of all multipoles, as determined by the angular momentum and parity selection rules, are included in the present work. The calculated values of (Kα ₂/Kα ₁), (Kβ ₁/Kα ₁), (Kβ ₃/Kβ ₁) and (Kβ ₂ Kβ ₁) transition rates are in good agreement with the available experimental data. Rates for the forbidden (M1) 2s _1/2→1s _1/2 transitions are also presented.     

Chemical shift of the Ga and As Kα1,2 and Kβ1,3 X-ray emission lines

By means of a double crystal spectrometer and a computer the chemical shifts of the Ga Kα_1,2, As Kα_1,2 and Kβ_1,3 lines were determined with high accuracy. An interpretation of the results obtained with a free ion model and a calculation according to the Hartree method shows agreement of the values calculated for the effective atomic charges with those based on chemical experience, and also the presence of a charge transfer from the A atom to the B atom in A^IIIB^V compounds. The existence of binding charges is one of the reasons for the fact that |q_A| ≠ |q_B|. The interpretation of the Kβ_1,3 and Lα shifts shows the limitations of the free ion model.     

The investigation of K‐shell fluorescence parameters of Zn–Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X‐ray fluorescence parameters (K_β/K_α, σ_Kα and σ_Kβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured K_α and K_βX‐ray production cross sections, and the K_β/K_αX‐ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in K_βX‐ray production cross‐section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.     

Shifts of X-ray characteristic L lines of free atoms of rare-earth metals

Results of the study of X-ray characteristic spectra of free atoms of a number of rare-earth metals from Ce to Ho are reported. L _α1 and L _β1 lines were studied, and the shifts of the peaks of emission lines of free atoms relative to their positions in the case of emission by the solid aggregate state were measured. The data obtained enable one to use the corresponding X-ray characteristic lines as references with the accuracy Δλ/λ≈10^?5. The Z-dependences of shifts are plotted.     

Zur Tiefenverteilung der durch Elektronenstoß angeregten charakteristischen Röntgenstrahlung von Bor,Kohlenstoff, Aluminium und Silber

The peak intensity of the X-ray emission bands of boron (BK; 67 Å), carbon (CK; 44 Å), aluminium (AlL _2,3; 171 Å), and silver (AgMζ; 40 Å) excited by electron bombardment of evaporated targets has been measured as a function of the thickness of the target and at several accelerating voltages in the range 1 to 4 kV. The electron beam was inclined at an angle of 50° to the surface of the target; the take-off angle for the radiation was about 20°. From these measurements one obtaines the thickness of layers effective in producing X-rays. The influence of surface contamination and oxide layers on the intensity distribution of emission bands is discussed. It is then shown that the effect of anode self-absorption can be evaluated, if the absorption coefficientμ(λ) is available. As an example theL ₃/L ₂ intensity ratio of aluminium, and an averaged depth of X-ray production are calculated; moreover data for the electron range are given and compared with earlier results. Finally the BK-emission band of evaporated boron is presented.