M.A. Respaldiza

Cadmium localization and quantification in the plant Arabidopsis thaliana using micro-PIXE

Remediation of metal-contaminated soils and waters poses a challenging problem due to its implications in the environment and the human health. The use of metal-accumulating plants to remove toxic metals, including Cd, from soil and aqueous streams has been proposed as a possible solution to this problem. The process of using plants for environmental restoration is termed phytoremediation. Cd is a particularly favourable target metal for this technology because it is readily transported and accumulated in the shoots of several plant species. This paper investigates the sites of metal localization within Arabidopsis thaliana leaves, when plants are grown in a cadmium-rich environment, by making use of nuclear microscopy techniques. Micro-PIXE, RBS and SEM analyses were performed on the scanning proton microprobe at the CNA in Seville (Spain), showing that cadmium is sequestered within the trichomes on the leaf surface. Additionally, regular PIXE analyses were performed on samples prepared by an acid digestion method in order to assess the metal accumulation of such plants.

CNA: The first accelerator-based IBA facility in Spain

Abstract The recently created Centro Nacional de Aceleradores (National Center for Accelerators, CNA) in Seville emerges as the first ion beam analysis facility in Spain. The laboratory is based on a 3 MV tandem accelerator model 9SDH-2 of NEC and it is primarily focused on material research and modification by means of IBA techniques: PIXE, RBS, NRA, PIGME and ERDA. The ions are delivered by two ion sources: Alphatross radio-frequency source and SNICS-II sputtering source. The ion beam handling system includes equipment for beam focusing, steering and diagnosis, a 90° analyzing magnet and a seven-port switcher magnet. A system based on magnetic steerers has been installed for high-precision beam energy scanning. In this paper the main elements of the laboratory will be described, focusing on the electronic equipment, detectors and the four beamlines planned for the moment: channeling line, microbeam line, multipurpose vacuum chamber and external microbeam. Moreover, the characteristics of the system as observed until now by means of performance tests, beam energy spread measurements and energy calibration experiments will be summarized.

Influence of preoxidation and annealing treatments on the isothermal oxidation in air at 1173 K of cerium-implanted EN-1.4301 stainless steel

Improvement of the high temperature oxidation behavior of conventional EN-1.4301 (AISI type 304) stainless steel was achieved by implanting cerium ions. Implantation was performed in samples with two different surface treatments: commercial 2B mill finishing and preoxidation in synthetic air. One set of samples was annealed after implantation in order to recover the damage induced in the crystalline structure. Results show that the implantation of Ce greatly improves the oxidation resistance at 1173 K of the EN-1.4301 grade stainless steels and that the annealing treatment after the implantation is beneficial during the subsequent oxidation. Experiments confirm the presence of spinel-type compounds and Cr2O3 and Fe–Cr mixed oxides with high Cr content in the scale, and martensite being the dominating metallic phase. Chromium depletion in the near-surface layers is also described. Results are compared to previously published data on surface modification using La and Ce by pyrolysis of aerosols.

External microbeam set-up at the CNA (Sevilla) and its application to the study of Tartesic jewellery

Abstract A new external microbeam system has been installed recently at the +45° beam line of the 3 MV Pelletron accelerator at the Centro Nacional de Aceleradores (Sevilla, Spain). The facility, based on the system from Oxford Microbeams (OM), includes two sets of slits, a doublet of magnetic quadrupole focusing lenses, a Faraday cup and an accurate positioning device. In addition, a beam profile monitor (BPM) and a quartz viewer have been installed in the line to facilitate the microbeam production. The first PIXE application of the new facility was made in the field of Archaeometry, on the study of Tartesic gold artefacts (700–500 BC, SW of Spain) from Ebora and other archaeological sites. The aim of the analysis was to perform an exhaustive and systematic study about the soldering procedures that were employed by the goldsmiths along the Valley of Guadalquivir River after the Phoenician colonisation.

Influence of the target and working gas on the composition of silicon nitride thin films prepared by reactive RF-sputtering

Abstract Silicon nitride thin films have been prepared at room temperature by RF reactive and non-reactive sputtering over several substrates. Pure silicon and high-density ceramic β-Si3N4 have been selected as two different target materials in order to study the properties of the obtained thin films. Additionally, different working sputtering gases have been selected to study their influence on the composition and properties of the obtained thin films. The relative composition and the absolute amount of nitrogen of the films have been determined by Rutherford backscattering spectroscopy and nuclear reaction analysis, respectively.

PIXE and SEM studies of Tartesic gold artefacts

Abstract Gold jewellery artefacts of Tartesic origin (700-500 B.C.) have been studied using external beams for quantitative PIXE. Collimators along the incident proton beam (2.7 MeV) allowed the artefacts to be irradiated in narrow regions down to 350 μm in diameter. Special attention has been paid to the procedure of soldering in various narrow regions of the bindings of filigrees, twisted wires, narrow strips and granulations on finely decorated items. By using reference materials and thick target PIXE programs including all matrix effects (X-ray cross sections, attenuation coefficients, secondary fluorescence), relative concentrations of Au, Ag and Cu in various regions have been determined. The results seem to indicate that solderings were made by local fusion and brazing. No procedure of solid state diffusion bonding like in Etruscan jewellery has been identified. Qualitative results using imaging and EDX induced by a very narrow electron beam (SEM) give complementary information to the quantitative determinations obtained from the PIXE measurements.

Thermal and photochemical methods for the preparation of thin films of cermet materials

The synthesis of thin films of Ag-SiO2, Ag-TiO2 and Ag-TiO2-SiO2 cermet materials is described. The preparation method consists in a sol-gel process based in the dip-coating technique to obtain thin films of a composite material containing the oxidized metal and the corresponding ceramic material (TiO2 and/or SiO2). The films, prepared on quartz, were finally heated or irradiated to induce the reduction of the metal and the formation of the cermet materials. An exhaustive characterization of the samples has been carried out by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Rutherford backscattering. The optical properties of the prepared thin films were determined by UV-VIS absorption spectroscopy and related to the microstructural characteristics of the cermet. Conclusions have been postulated to relate the experimental conditions of the synthesis (thermal or photochemical) to the microstructure and properties of the resulting materials.

Environmental impact of fertilizer industries evaluated by PIXE

In this paper the environmental impact of several phosphogypsum piles sited in the southwest of Spain is studied using multielemental analysis by PIXE of 12 salt marsh and soil samples collected in their surroundings. The piles are used to store the main by-product formed in the production of phosphoric acid and phosphate fertilizers. The samples collected were bombarded with 2.5 MeV protons from the 3 MV Van de Graaff accelerator in the ITN at Sacavem (Portugal), and 20 elements from Al to Pb were detected. The results obtained reinforce previous radioanalytical determinations concerning the significant radioactive contamination pathways (leaching or/and dissolution of elements by water from the piles) and the negligible pathways (atmospheric and direct aquatic transport).

TTPIXE analysis of Guadiamar river sediments collected before the environmental disaster of 1998

Abstract Thirteen sediment samples were collected along the Guadiamar riverbed (SW of Spain) in the spring of 1996 for the determination of their composition by thick target proton induced X-ray emission (TTPIXE), using the accelerator of the ITN (Portugal). Our results indicate a S, Cu, Zn, As and Pb contamination along the riverbed due to the mining activity developed around the beginning of the Guadiamar river. The obtained results will serve, in first place, as reference levels to show the situation of the riverbed before the environmental disaster of mining origin occurred in April 1998, and in second place, to evaluate properly in the future the works carried out for the cleaning and restoration of the affected areas.

The response of a chromium doped alumina screen to keV and MeV ions

We have characterised the response of a chromium-doped alumina screen ‘Chromox’ to light ions (H+ and He+) accelerated to keV and MeV energies. In particular, we have determined the absolute luminosity in terms of the number of photons emitted per incident ion from the front and back faces of such a screen. This work has been motivated by the application of this material to a diagnostic for measuring fast ion losses, close to the plasma edge, from the hot plasmas in fusion devices, where its radiation hardness, compared to that of standard phosphors, makes it very attractive. We also discuss the persistent afterglow observed after removal of the ion beam in terms of its cause and possible repercussions for this diagnostic.