Elemental analysis of mining wastes by energy dispersive X-ray fluorescence (EDXRF)

An energy dispersive X-ray fluorescence (EDXRF) tri-axial geometry experimental spectrometer has been employed to determine the concentrations of 13 different elements (K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr and Pb) in mine wastes from different depths of two mine tailings from the Cartagena-La Union (Spain) mining district. The elements were determined and quantified using the fundamental parameters method. The concentrations of Cr, Ni, Cu, Zn and Pb were compared to the values from the European and Spanish legislation to evaluate the environmental risk and to classify the wastes as inert wastes or as wastes that have to be control land-filled. The results obtained demonstrate that these wastes can be considered as inert for the considered elements, apart from the concentration levels of Zn and Pb. Whilst Zn slightly overpasses the regulatory levels, Pb mean value exceeds three to six times the value to be considered as Class I potential land-filling material.     

X-ray absorption in atomic potassium

A new high-temperature absorption cell for potassium vapor is described. X-ray absorption coefficient of atomic potassium is determined in the energy interval of 600 eV above the K edge where thresholds for simultaneous excitations of 1s and outer electrons, down to [1s2p] excitation, appear. The result represents also the atomic absorption background for XAFS (X-ray absorption fine structure) structure analysis. The K ionization energy in the potassium vapor is determined and compared with theoretical data and with the value for the metal.     

Photon emission mechanisms of different phosphors

A comparison is made between the different mechanisms involved in the electron and photon excitation processes of four different phosphors. The green luminescence peak of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphor is normally asymmetrical and tails towards the longer wavelengths. The observed peak in the longer wavelength region is associated with preferential alignment of one of the Eu²⁺ d-orbitals. Four Gaussian peaks fitted to the cathodoluminescent (CL) and photoluminescent (PL) spectra of broad band emission spectra of X₁-Y₂SiO₅:Ce phosphor may be attributed to the two different sites (A1 and A2) of the Ce³⁺ ion in the host matrix and the difference in orientation of the neighbour ions in the complex crystal structure. Co-activation of Ce³⁺ with Eu³⁺ quenches the red emission from Eu³⁺ and considerably increases the blue emission from Ce³⁺ in a SiO₂ matrix. In nanoparticulate PbS the emission data show a blue shift from the normal emission at ∼3200 nm in PbS bulk to ∼560-700 nm. The blue shifting of the emission wavelengths from 3200 to ∼560-700 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles.     

Self-radiation damage in plutonium and uranium mixed dioxide

In plutonium compounds, the lattice parameter increases due to self-radiation damage by α-decay of plutonium isotopes. The lattice parameter change and its thermal recovery in plutonium and uranium mixed dioxide (MOX) were studied. The lattice parameter for samples of MOX powders and pellets that had been left in the air for up to 32 years was measured. The lattice parameter increased and was saturated at about 0.29%. The change in lattice parameter was formulated as a function of self-radiation dose. Three stages in the thermal recovery of the damage were observed in temperature ranges of below 673 K, 673-1073 K and above 1073 K. The activation energies in each recovery stage were estimated to be 0.12, 0.73 and 1.2 eV, respectively, and the corresponding mechanism for each stage was considered to be the recovery of the anion Frenkel defect, the cation Frenkel defect and a defect connected with helium, respectively.     

Determination of bulk etch rate for CR-39 nuclear track detectors using an X-ray fluorescence method

The thickness of a CR-39 detector is determined using an energy dispersive X-ray fluorescence (EDXRF) method of analysis. The method is based on exciting a suitable target and measuring the intensity of its fluorescence X-ray lines passing through the CR-39 sample in a fixed geometry. By properly selecting the target material, the method succeeds in assessing the thickness change of CR-39 detectors etched for different time intervals. The bulk etch rate (V_b) may thus be obtained, which is an important parameter for any solid state nuclear track detector. Application of the EDXRF method yielded a value of V_b = (2.01 ± 0.04) μm h⁻¹ for etching in a 6 N NaOH solution at 75 °C. This value agrees with the bulk etch rate of (1.90 ± 0.03) μm h⁻¹, obtained by the conventional mass-change method.     

Quality assessment system for curved crystal X-ray optics

Doubly curved crystal X-ray optics provide intense focused monochromatic beams from laboratory X-ray tube sources. These optics are employed in crystallography and X-ray fluorescence systems and may find application to imaging. It is increasingly important to understand how optic defects impact performance for these systems. A simulation model was developed to assess the effects of misalignment and optic defects on system parameters such as intensity, beam size and resolution. Simulation results were compared to optics measurements. Rapid reproducible measurements of optics quality are important both for performing systematic studies of optics defects and for assessing individual optics. A simple operator-independent alignment technique was developed that was also beneficial in ensuring optimal beam intensity in analysis systems. The measurements and simulations were in good agreement and provided insight into essential optics parameters.     

Chemical shift measurements of chlorine K X-ray spectra using a high-resolution PIXE system

A high-efficiency high-resolution wavelength-dispersive spectrograph with a von-Hamos configuration was developed for chemical state identification of elements in environmental samples using PIXE analysis. To evaluate the performance of this system, chlorine K X-ray spectra for NaCl, NH₄Cl and polyvinylchloride (PVC) targets were measured and compared. Also, to study the applicability to environmental mixed samples, mixtures of NaCl and NH₄Cl with different mixing ratios were measured. Through observation of Cl Kα₁ X-ray from NaCl, the energy resolution of the system was determined to be 1.1 eV. For the NaCl sample, a Kβ_x line was observed at an energy, which is higher than that of the Kβ main peak by 2 eV, whereas no Kβ_x emission was observed for the NH₄Cl sample. The chemical shift of the Kβ main peak for PVC relative to that for NaCl was about 1.2 eV. For NaCl-NH₄Cl mixture targets, the relative intensity of Kβ_x satellite to the Kβ main line provided an indication of mixing ratio. Energies and relative intensity of Cl Kβ X-ray satellites for NaCl and NH₄Cl samples calculated by a simple molecular-orbital method agreed only qualitatively with the experimental results.     

An energy dispersive micro X-ray diffractometer based on a combined system of polycapillary optics

An energy dispersive micro X-ray diffractometer based on a combined system of two polycapillary X-ray lenses is designed. The polycapillary X-ray lens in the excitation channel is either a polycapillary parallel X-ray lens (PPXRL) or a slightly focusing polycapillary X-ray lens (SFPXRL). The polycapillary X-ray lens in the detection channel is a PPXRL. At 6.4 keV and 2θ = 141.5°, the total resolution of the diffractometer based on a SFPXRL in the excitation channel and a PPXRL in the detection channel in Δd/d is 4.8%.     

Autoionization of N (q = 1-3) Rydberg states produced in high-energy collisions with He

Energy spectra of electrons ejected through autoionization decay of high-Rydberg states in high-energy collisions of N^q+ (q = 1-3) with He have been measured with high-resolution by using zero-degree electron spectroscopy. Several series of autoionizing lines were observed, corresponding to decays from N³⁺ 1s²2p(²P)nl Rydberg states produced in N³⁺ + He collisions, from N²⁺ 1s²2s2p(³P)nl Rydberg states produced in N²⁺ + He and from N⁺ 1s²2s2p²(⁴P)nl Rydberg states produced in N⁺ + He, respectively. Angular momentum distributions for the first or second peak of three series of Coster-Kronig electron transitions for N^q+ (q = 1-3) projectiles are also discussed, where the highly excited states are formed by electron excitation.     

External-beam PIXE characterization of volcanic material used in ancient Roman mortars

Volcanic deposits from two volcanic districts, Monti Sabatini (MSVD) and Colli Albani (CAVD), NW and SE of Rome, were analyzed using the particle-induced X-ray emission (PIXE) technique, in order to obtain chemical fingerprints that can be used for provenance studies of filler materials in ancient Roman mortars. The rock samples were mounted on an X-Y stage enabling scanning over the sample surface and irradiated in air with a collimated 3 MeV proton beam. The samples were either analyzed by scanning the beam over a polished surface or they were crushed, ground and homogenized prior to the irradiation. However, scanning over polished sample surfaces avoiding heterogeneities gave quite similar results as scanning over pellet surfaces, especially for the minor and trace elements. This study shows that the deposits of MSVD and CAVD can be distinguished from each other. Several elements or elemental ratios can be used to characterize the districts. Even the individual volcanic deposits of CAVD can be identified.     

Analysis of elemental maps from glaze to body of ancient Chinese Jun and Ru porcelain by micro-X-ray fluorescence

The reasons how the middle layer of Ru and Jun porcelain between the glaze and body came into being are still not completely understood. Here, elemental maps from the glaze to the body of pieces of ancient Chinese Ru and Jun porcelain were analyzed by micro-X-ray fluorescence. The results show the middle layer was probably formed by the chemical composition of the glaze turning into glassy states and undergoing complex physical-chemical reactions with the body. However, the middle layer of Jun porcelain was formed by the chemical composition of the glaze turning into glassy states and then infiltrating the body at high temperatures during the firing process.     

Characterization and applications of a new tabletop confocal micro X-ray fluorescence setup

A tabletop confocal three-dimensional micro X-ray fluorescence (3D micro-XRF) setup was designed, based on polycapillary X-ray optics and a micro-focus X-ray source. This confocal setup consists of a polycapillary full lens to focus the incident beam and a polycapillary half lens to collect the X-ray fluorescence. The confocal volume was proved to be ellipsoidal. The full-width at half maximum (FWHM) of the confocal volume in three directions were measured with a “knife edge” scan method to obtain the spatial resolution of the confocal setup. The structure of multilayer samples was studied using the depth scan technique.     

Multianalytical characterization of a blue pigment used in art-crafts from Central Mexico

We report a preliminary characterization of a blue pigment because its color has been associated to objects found from Aztec and Precolumbian times. The pigment was examined before and after its purification by a variety of techniques: Particle Induced X-ray emission (PIXE), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy coupled to energy dispersion spectroscopy (SEM-EDS). The relationship of the chemical composition, the spectroscopic signals and the color are discussed.     

Determination of the effective atomic numbers and electron densities for YBaCuO superconductor in the range 59.5-136 keV

The effective atomic numbers and electron densities of YBa₂Cu₃O_7−δ superconductor at 59.5, 65.2, 77.1, 94.6, 122 and 136 keV were calculated by using the measured mass attenuation coefficients. Measurements were made by performing transmission experiments in a well-collimated narrow beam geometry set-up by employing Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. These values are found to be in good agreement with theoretical values calculated based on XCOM data. The observed crystal structure of YBa₂Cu₃O_7−δ superconductor is close to the theoretical structure. Z_eff and N_el experimental values showed good agreement with the theoretical values for calcined and sintered YBa₂Cu₃O_7−δ.     

Effects of the behaviour of the proton-induced isotopes production on the analysis of ancient alloys

The present work concerns non-destructive ion beam analysis carried out by means of proton-beam-induced nuclear reactions in the 10-30 MeV energy range. We focused our attention on the yield distribution of the isotopes produced in the internal region of a metal alloy. This distribution, which defines the analytical region, displays, at incident energy of about 20 MeV in a bronze based alloy, a bell-shaped curve centred at about 600 μm with an average width of about 400 μm. By changing the incident proton energy it is possible to displace the above region in the interior of the metal body. It should be pointed out that if we neglect to take into account the correct behaviour of the isotope yield distribution in samples with surface inhomogeneities we can obtain erroneous analytical results. We describe some experiments based on proton activation analysis (PAA) carried out at the INFN-Laboratori Nazionali del Sud (LNS) in Catania where we verified the bell-shape of the radioactive isotope distribution. The resulting formulas are given for quantitative analysis.It is straightforward that, by choosing the appropriate incident proton energy, it is possible to confine the whole analytical region to the interior of the body, thus eliminating any influence of surface effects. We have called this particular approach deep proton activation analysis (DPAA). Examples of its use on archaeological artefacts are given.     

A systematic study on MOS type radiation sensors

Radiation sensors based on metal oxide semiconductor (MOS) structure are useful because of their superior sensitivity as well as excellent compatibility with the existing microelectronic technology. In this paper, a systematic study of MOS capacitors built on p- and n-type Si substrates with different SiO₂ thicknesses (10 nm, 50 nm, 100 nm and 240 nm) is presented. MOS device response to gamma radiation up to 256 Gray have been studied from the sensor application point of view. Variation of the radiation induced device response with oxide thickness, substrate type, applied bias and post annealing have been measured and discussed. Radiation induced charge in MOS devices is shown to be a strong function of the oxide thickness as expected. Application of a positive bias to the gate is found to enhance the device sensitivity for both n- and p-type devices. This is explained in terms of the involvement of the interface states in the sensing process. Devices have also been studied after repeated cycles of irradiation and annealing treatment under hydrogen atmosphere. Each cycle consists of gamma irradiation with 60 Gray dose and an anneal at 200 °C for 30 min. The charging-discharging mechanism during these cycles is discussed.     

Differential and scanning-mode external PIXE for the analysis of the painting “Ritratto Trivulzio” by Antonello da Messina

Extensive PIXE investigations have been performed at the LABEC accelerator laboratory in Florence on the painting “Ritratto Trivulzio” by Antonello da Messina, one of the great Italian masters of XV Century and a pioneer in modern oil painting.It is well known that a complete and unambiguous characterisation of materials in paintings is often difficult, owing to their complex structure. For the “Ritratto Trivulzio”, the combination of advanced variants of PIXE, such as differential and scanning-mode analysis, provided a relevant contribution to the characterisation of paint layers, in terms of composition and structure, in a totally non-invasive and non-destructive way.Single-spot mode PIXE with external proton beams of about half millimetre diameter was first used for a general characterisation of different areas of the painting. Differential PIXE performed in many spots led to reconstruct the sequence of paints employed by the artist and to estimate in some cases the local paint layer thickness.A second run carried out with the external scanning microbeam facility, using a 3 MeV proton beam of about 80 μm size, was then crucial to clarify some issues raised by the first analysis. In particular, elemental maps from selected areas helped to understand the way some colour shades had been obtained on the red mantle of the portrayed gentleman, using different pigments irregularly distributed on the surface.     

Angular distributions of diffracted X-ray radiation from channeled electrons in Si and LiF Crystals: Influence of energy levels band structure

It is shown that the band structure of the energy levels of planar channeled electrons qualitatively changes the angular distributions of X-rays emitted at Bragg angles.     

Determination of K shell absorption jump factors and jump ratios in the elements between Tm(Z = 69) and Os(Z = 76) by measuring K shell fluorescence parameters

The K shell absorption jump factors and jump ratios have been measured in the elements between Tm (Z = 69) and Os(Z = 76) without having any mass attenuation coefficient at the upper and lower energy branch of the K absorption edge. The jump factors and jump ratios for these elements have been determined by measuring K shell fluorescence parameters such as the total atomic absorption cross-sections, the K_α X-ray production cross-sections, the intensity ratio of the K_β and K_α X-rays and the K shell fluorescence yields. We have performed the measurements for the calculations of these values in attenuation and direct excitation experimental geometry. The K X-ray photons are excited in the target using 123.6 keV gamma-rays from a strong ⁵⁷Co source, and detected with an Ultra-LEGe solid state detector with a resolution 0.15 keV at 5.9 keV. The measured values have been compared with theoretical and others’ experimental values. The results have been plotted versus atomic number.