Roman bronze artefacts from Thamusida (Morocco): Chemical and phase analyses

Twenty-six objects (1st to the 3rd century AD) found at the archaeological site of Thamusida (Morocco), which is a military settlement between the 1st and the 3rd century AD, have been investigated by means of portable X-ray fluorescence and time of flight-neutron diffraction. The combination of element-sensitive X-ray fluorescence and structure-sensitive neutron diffraction yields, in a totally non-destructive way, the necessary information to discriminate the copper alloy from corrosion and alteration layers. Results allowed dividing the repertory into five groups: (a) unalloyed copper, (b) binary alloys made of Cu and Sn, frequently leaded; (c) unleaded binary alloys made of Cu and Zn; (d) ternary alloys made of Cu, Sn and Zn, both leaded and unleaded; (e) quaternary alloys made of Cu, Sn, Zn and As. The choice of alloy is heterogeneous, mainly depending on availability and costs of raw and/or scrap materials and on technological constraints. Interestingly, the reconstruction obtained for Thamusida could either anticipate the important change in the Roman use of copper alloys generally referred as ‘zinc decline’, or more likely, indicate that brass never conspicuously entered the local metal-working activities of this military site.     

Measurement of L X-ray fluorescence cross-sections for elements with 45 ? Z ? 50 using synchrotron radiation at 8 keV

The L shell fluorescence cross-sections of the elements in range 45 ? Z ? 50 have been determined at 8 keV using Synchrotron radiation. The individual L X-ray photons, Ll, Lα, Lβ_I, Lβ_II, Lγ_I and Lγ_II produced in the target were measured with high resolution Si(Li) detector. The experimental set-up provided a low background by using linearly polarized monoenergetic photon beam, improving the signal-to-noise ratio. The experimental cross-sections obtained in this work were compared with available experimental data from Scofield [1] and [2] Krause [3] and [4] and Scofield and Puri et al. [5] and [6].These experimental values closely agree with the theoretical values calculated using Scofield and Krause data, except for the case of Lγ, where values measured of this work are slighter higher.     

Detection and analysis of the microdistribution of uranium in the gills of freshwater Corbicula fluminea by SIMS technique

The microdistribution of uranium in the gills of freshwater bivalve Corbicula fluminea following chronic direct exposure to this radioelement has been investigated using the SIMS technique. Different exposure levels and exposure durations have been studied. The SIMS mass spectra and ²³⁸U⁺ ion images produced with a SIMS CAMECA 4F-E7 show an U accumulation with the lower aqueous U concentration (20 μg/L) and the influence of the exposure levels on the bioaccumulation capacities. Furthermore, the ionic images display a heterogeneous distribution of uranium within the gill structure whatever the exposure conditions are. This study, in keeping with the ENVIRHOM French research program, was led to the conclusion that ion microscopy is an appropriate analytical method for trace elements and can give elemental cartography in a biological tissue section.     

COOH ion implantation-modified indium tin oxide electrode for the direct electrochemistry of cytochrome c

A COOH⁺ ion implantation-modified indium tin oxide (COOH/ITO) electrode was prepared and the existence of carboxyl group on the electrode was verified by X-ray photoelectron spectroscopy analysis. The field emission-scanning electron microscope result showed that the ion implantation formed many active centers on the ITO surface. The COOH/ITO electrode was applied for cytochrome c (cyt c) immobilization and the electrochemical behaviors of cyt c were evaluated by cyclic voltammetric techniques. The results demonstrated that the immobilized cyt c retained its electrocatalytic activity to the reduction of H₂O₂. This ion implantation-modified electrode might be used in development of new biosensors and biofuel cells.     

Energy spectra measurements of X-ray emission from electron interaction in a dense plasma focus device

Electrons generated during a pinch implosion in a hollow anode Mather-like plasma focus device (PF) are considered as a possible X-ray source via the impinging of those particles on medium and high-Z targets. A usual PF device has been slightly modified to optimise the X-ray production and their measurements by means of a suitable and non-invasive spectrometer. This ensemble allows measurements of X-rays generated booth by electrons turning back to the anode and by target collision of the so-called relativistic electron beam. The spectrum of the emitted photons is evaluated by using a differential absorption based technique. The X-ray spectrometer consists of a stack of LiF dosimeters which act both as detectors and filters to give curves of attenuated intensities. Finally, the energy distribution is calculated from such attenuation curves using an iterative procedure based on spectral algebra formalism.     

Evaluation of dominant time-eigenvalues of neutron transport equation by Meyer’s sub-space iterations

The aim of this paper is to explore the use of Meyer’s sub-space iteration (SSI) method for the evaluation of dominant prompt time-eigenvalues of the neutron transport equation. The integro-differential form of the transport equation is considered. The SSI method is known to be an efficient technique to find the dominant eigenvalues of a non-symmetric matrix. It has been earlier used for eigenvalue problems in neutron diffusion theory. However, it does not seem to be tried in the transport theory case. Here, the use of SSI has been tested in transport theory for some 1-D mono-energetic homogeneous and heterogeneous benchmark problems. The space variable is discretised by finite differencing while neutron directions are discretised by discrete ordinates (S_n-) method. The SSI method needs frequent multiplication of the relevant matrix operator with vectors. As known from earlier works in this area, this can be achieved in terms of external source calculations for which a 1-D programme was developed and used. With the availability of more versatile S_n-method codes, it may perhaps be possible to extend use of SSI to more realistic cases.     

Relative intensities for Li (i = 1-3) and Mi (i = 1-5) subshell X-rays

The intensities for L_i (i = 1-3) subshell X-ray lines have been computed relative to the most intense line in each series, for elements with 30 ? Z ? 92, from published X-ray emission rates based on the Dirac-Fock (DF) model. In the case of M_i (i = 1-5) subshell X-ray lines, complete sets of emission rates based on both the Dirac-Hartree-Slater and the DF models have been generated for elements with 65 ? Z ? 92 by logarithmic interpolation of the data available for a limited number of elements. The intensities for different M X-ray lines have been computed relative to the most intense line in each series using these two sets of emission rates. The L_i (i = 1-3) and M_i (i = 1-5) subshell X-ray relative intensities computed from the DF model based emission rates have been least-squares-fitted to polynomials in the atomic number for use in software packages for quantitative elemental analysis using X-ray emission techniques and for other applications.     

An X-ray structural analysis of cesium substitution in the barium hollandite phase of synroc

The X-ray structures of polycrystalline barium hollandite with cesium partially substituting for barium (viz [Ba_xCs_y] [Al_2x+yTi_{8 ? 2x ? y}]O₁₆) have been determined using the Rietveld refinement technique. Electron microprobe results indicate that the level of cesium substitution is constrained by the condition that the total volume occupied per unit cell by the cesium and barium ions remains substantially constant. X-ray refinement revealed that the structural parameters defining the positions of the titanium, aluminium and oxygen ions are not affected greatly by cesium substitution. The only significant change occurs in the parameter z which defines the average Cs/Ba position. This increases with the level of cesium indicating that these ions tend to occupy a more central location with respect to their coordinating oxygen ions. An analysis of the (Cs/Ba)-O bond lengths suggests a limit of structural stability corresponding to 0.25 cesium ions per unit cell.     

Effect of crystallinity on the memory effect of Ge nanocrystals synthesized by atom beam sputtering

The effect of crystallinity of Ge nanocrystals on the charge storage properties of the metal oxide semiconductor (MOS) structure has been investigated. MOS structure with Ge nanocrystals embedded in the oxide has been fabricated by using atom beam sputtering technique. After annealing at 600 °C in Ar + H₂ atmosphere, capacitance-voltage (C-V) measurements show flat band voltage shift of ∼0.9 V. It which is a clear indication of the memory effect of Ge nanocrystals, while unannealed structure doesnot show any hysteresis in the C-V curve. Micro Raman spectroscopy and X-ray diffraction (XRD) analyses show that crystalline content of Ge nanoparticles in the MOS structure has increased after annealing.     

The systematics of (n,2n) reaction excitation function

Based on the constant temperature evaporation model taking the competition of (n,3n) reaction and the contribution of preequilibrium emission into account, the systematics formulae of (n,2n) reaction excitation function have been established. The systematics behaviours of (n,2n) reaction excitation function have been studied. There are two systematics parameters T and σ_n,M, and can be adjusted in the formulae. For getting the two parameters, the new evaluated data of (n,2n) reactions were adopted and fitted by means of the nonlinear least squares method. The fitted results agree fairly well with the measured data at below 30 MeV. Based on a body of new measurements, the reliability to predict (n,2n) reaction excitation function is improved. Hence more accurate systematics prediction for unmeasured nucleus or energy range may be provided.     

Saturable absorption in gold implanted fused silica

Metal nanocluster composite glasses (MNCGs) have been the subject of both experimental and theoretical investigation because of their peculiar optical properties. In particular, the enhanced third order optical nonlinearity could be exploited in the all-optical switching device technology. In the present work, we present some results on MNCG films prepared by ion implantation. Fused silica were implanted with Au⁺ of fluences 3 × 10¹⁶ and 1 × 10¹⁷ ions/cm² using an energy of 1.5 MeV. Optical absorption spectra of these samples have revealed prominent linear absorption bands at characteristic surface plasmon resonance (SPR) wavelength at and around 490 nm. Rutherford backscattering spectrometry (RBS) measurements reveal a Gaussian spatial distribution of Au ions. Third order optical nonlinear properties were studied by the Z-scan technique using a nanosecond laser. Z-scan measurements on the metal nanoclusters glass composites have revealed saturable absorption signifying the nonlinear responses.     

Software masking for the accurate determination of elemental quantities in discrete areas of a micro-PIXE scan

A technique is described which allows X-ray energy spectra corresponding to discrete regions of a micro-PIXE scan recorded in multi-parameter mode to be generated. A software mask is created using both user-defined rectangular limits and an algorithm operating on the distribution of one of the major elements in the sample. This mask is used to select X-ray events originating in the region of interest, from which elemental concentrations can be calculated. This technique can allow accurate determination of element concentrations in irregular samples or regions of interest, enhance the signal-to-noise ratio for specimens on thick backings and also allows several areas of the sample to be analysed separately. The use of the technique is demonstrated in an experiment to quantify the total mass of barium contained in a single cell alga (Closterium tumidulum).     

X-ray scattering in X-ray fluorescence spectra with X-ray monochromatic, polarised excitation - Modelling, experiment, and Monte-Carlo simulation

A systematic series of measurements has been carried out with monochromatic X-ray excitation with synchrotron radiation in order to check a physical model on X-ray scattering. The model has recently been successfully tested for the case of polychromatic, unpolarised excitation emitted by an X-ray tube. Our main purpose is the modelling of a physical background in X-ray fluorescence spectra, so that improved quantitative results can be achieved especially for strongly scattering specimens. The model includes single Rayleigh and Compton scattering in the specimen, the effect of bound electrons, the challenging Compton broadening and the polarisation degree. Representative specimens, measurement geometries and excitation energies have been selected with synchrotron monochromatic light at BAMline/BESSY II. Monte-Carlo simulations have been also carried out in order to evaluate the quality of the results achieved with the model.     

Measurement of focal spot size in a 5.5 MeV linac

High energy X-ray beams allow to perform analysis on different materials and objects of relevant interest that cannot be investigated with conventional X-ray sources. A 5.5 MeV endpoint energy bremsstrahlung source has been characterized by evaluating the size of X-ray emitting area. In order to perform a proper characterization, an ‘ad hoc’ slit-camera has been designed and a specific technique has been adopted. Due to the characteristics of the beam, a highly attenuating slit with variable aperture has been designed using Monte Carlo simulations of the X-ray beam and set up. Since the slit camera is far from the ideal model (negligible X-ray transmission and very thin aperture), a whole set of image profiles of the slit at different width sizes have been acquired and analyzed. Imaging correction procedures and data fitting lead to satisfactory experimental results according to the theoretical model.     

Proton induced L-shell X-ray production cross-sections for Pb in the energy range 225–400 KeV

The L-shell X-ray production cross-sections in lead (Pb) by proton impact over the energy range 225–400 keV, with an interval of 25 keV, have been measured. The thick target X-ray yields have been obtained using a HPGe detector. The experimental results for σ_L1, σ_Lα, σ_Lβ and σ_Lγ have been compared with perturbed stationary state theory with relativistic (R), energy loss (E) and Coulomb (C) corrections (ECPSSR theory). The comparison of L_α, L_β and L_γ, X-ray production cross-sections shows a fairly good agreement, except at the lowest energy. The L₁ X-ray production cross-sections are higher by ≈ 20–30% than their theoretical estimates.     

Higher order mode analyses in Feynman-α method

Using a generalized formula for the space and energy dependent Feynman-α method, which was originally derived by Endo et al. and Muñoz-Cobo et al., the effect of higher order modes of the α-mode eigenvalue problem on the Feynman Y function has been investigated. To deal with a large number of higher order modes, the diffusion approximation is adopted instead of the transport theory for a one-dimensional homogeneous infinite slab. By making a transport correction to low order mode eigenvalues and eigenfunctions, the formula can accurately reproduce the Monte Carlo simulation results of the Feynman-α method. By virtue of these efforts, an accurate numerical application of the generalized formula, which has not been performed due to the difficulty in solving the higher order α-mode eigenvalue problem, has been made possible. Sample numerical examples for a near-critical system and a deeply-subcritical system quantitatively demonstrate how the Feynman Y functions are decomposed into the higher order mode components. While the higher order mode components in the Feynman Y function can be negligible in a near-critical system, the Feynman Y function in a deeply-subcritical system is found to be severely contaminated by the higher order modes.     

PIXE and RBS analysis of Tl-1223 superconducting phase substituted by scandium

Ion beam analysis techniques (IBA) were performed to determine the elemental stoichiometry of superconducting samples of type TlBa₂Ca_2−xSc_xCu₃O_9−δ, with 0 ? x ? 0.6, prepared via solid-state reaction technique. By combining particle induced X-ray emission (PIXE) with Rutherford backscattering spectrometry (RBS), the stoichiometry of the samples is determined. However, the oxygen content is obtained by using non-Rutherford backscattering cross-section at 3 MeV proton beam. Furthermore, the prepared samples were also characterized using X-ray powder diffraction (XRD) and electrical resistivity measurements. The X-ray data indicate that the partial substitution of Ca²⁺ by Sc³⁺ ions does not affect the tetragonal structure of Tl-1223 superconducting phase. The superconducting transition temperatures T_c, determined from electrical resistivity measurements, was found to be highly correlated to the Sc-content.     

Study of the long term effect of high gamma doses in the crystalline phase of P(VdF-TrFE) copolymers

Differential Scanning Calorimetry (DSC) and X-ray diffraction (XRD) of gamma irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer [P(VdF-TrFE)] have been studied in connection with the use of material in industrial high gamma dose measurement. Interaction between radiation and P(VdF-TrFE) results in a decrease of its crystallinity together with the simultaneous formation of CC conjugated bonds. It has been found that the melting latent heat (L_Melt) of the crystallites is unambiguously related to the value of absorbed dose. The DSC technique can be used to evaluate high gamma doses ranging from 1.0 kGy to 1.0 MGy. The relation between L_Melt and gamma doses can be fitted by an exponential function for measurements taken until 3 months after irradiation. After this time, the relation can be fitted by a linear function for periods at least of one year. X-ray diffraction revealed an expansion of the β-phase unit cell of 5% in the b direction for gamma doses between 250 and 500 kGy. The results presented highly increases the possibility of using the melting latent heat of P(VdF-TrFE) copolymer in high dose dosimetry.     

Analysis method of Charpy V-notch impact data before and after electron beam welding reconstitution

The specimen reconstitution technique is one of the most promising techniques to improve the surveillance program of the reactor pressure vessel (RPV). In this study, unirradiated 30Mn2V low-alloy steels were chosen as the test materials, and the broken halves of Charpy V-notch impact (CVN) specimens were reconstituted to be new CVN specimens by the electron beam welding (EBW) as a pilot study in China. Taking the 20 insert reconstituted specimens as an example, Boltzmann function was used to fit the CVN data, the ductile-brittle transition temperature (DBTT) and its uncertainty were evaluated, and the equality of DBTT between the reconstituted specimens and original specimens was checked by t/t′-test. There is a great consistency between CVN data of EBW reconstituted specimens and that of original specimens.     

Electronic stopping dependence of ion beam induced modifications in GaN

We report here Swift heavy ion induced effects in GaN samples grown by metal organic chemical vapor deposition (MOCVD) technique. These samples were irradiated with 80 MeV Ni and 100 MeV Ag ions at a fixed fluence of 1 × 10¹³ ions/cm². Ion species and energies are chosen such that the difference in their electronic energy loss (S_e) would be 8 keV/nm. Effects of Ag on structural and optical properties over Ni ions have been discussed extensively. We employed different characterization techniques like High Resolution X-ray Diffraction (HRXRD) and Raman Spectroscopy for defect density calculations and for vibrational modes, respectively. Defect densities are calculated and compared using Williamson-Hall method from HRXRD. Change of strain and vibrational modes with S_e has been discussed.