C.A. Pineda-Vargas

Characterisation of natural and enriched oxygen targets in lithium carbonate foils

A method for making oxygen targets in a form of lithium carbonate compound is described. Targets were prepared for nuclear physics experiments which required oxygen with a mass greater than 60xa0%. Both natural and isotopic enriched targets of 18O with thicknesses of less than 1xa0mg/cm2 were produced and characterised by elastic recoil detection analysis and elastic backscattering techniques. The results obtained showed that enriched foils had limited isotopic exchange when exposed to air and good stability with time compared to foils with natural oxygen.

Characterisation of thin solid Xe targets

A series of frozen xenon targets of thicknesses ranging between 1 and 15xa0mg/cm2 were characterised by elastic backscattering technique using a 3xa0MeV proton beam. Xenon was kept solid on a gold substrate having a thickness of 1xa0g/cm2 which was mounted on a cold copper finger. The temperature of targets during the experiment was maintained at 55xa0K by a compact solid nitrogen sublimation system under pressure of 10−5 mbar. Targets were used in series of experiments for populating samarium and gadolinium isotopes in the 136Xe (18O, Xn) and 136Xe (22Ne, Xn) nuclear reactions.

Application of particle-induced X-ray emission, backscattering spectrometry and scanning electron microscopy in the evaluation of orthodontic materials

The focus of this investigation was on orthodontic materials used in the manufacture of dental brackets. The properties of these dental materials are subjected to various physical parameters such as elongation, yield strength and elasticity that justify their application. In turn, these parameters depend on the quantitative elemental concentration distribution (QECD) in the materials used in the manufacture. For compositional analysis, proton-induced X-ray emission (PIXE), backscatter spectrometry (BS) and scanning electron microscopy (SEM) were applied. QECD analysis was performed to correlate the physical parameters with the composition and to quantify imperfections in the materials. PIXE and BS analyses were performed simultaneously with a 3xa0MeV proton beam while electrons accelerated at 25xa0keV were used for the SEM analysis. From the QECDs it was observed that: (1) the major elements Cr, Fe and Ni were homogeneously distributed in the orthodontic plate; (2) the distribution of Mo and O correlated with one another; (3) there was a spread of Cr around regions of high C concentration; and, (4) areas of high concentrations of Mo and O corresponded to a decrease in C concentrations. Elemental concentration correlations are shown to indicate the similarities and differences in the ease of formation of phases, based on the tangent of linearity.

Micro-PIXE Analysis Of Bioconductive Hydroxyapatite Coatings On Titanium Alloy

Bioconductive materials and in particular implants using Ti alloy (Ti6–Al4–V) coated with hydroxyapatite (HAp) have proved to be a suitable surgical procedure. However, experience has shown that these implants not always have the required reliability to guarantee their expected life-span of approximate 15xa0years. In this research, experimental Ti alloy-implants coated with HAp and incubated in a simulated body fluid (r-SBF) under controlled physiological conditions were studied by nuclear microprobe (NMP). Selected HAp coatings, were analysed by micro-PIXE using protons of 1.5xa0MeV at the iThemba LABS NMP facility. Major elements (Ti, Al, V, Ca and P) as well as trace elements (Si, K, Fe, Zn and Sr) were determined. The effect of longer incubation time was of particular interest. Results confirmed that secondary Ca-deficient defect hydroxyapatite precipitated from the simulated body solution onto the HAp coating surface after prolonged incubation. This newly formed layer is thought to be of vital importance for bonding of implants with living bone tissue.