C.A. Pineda

The NAC nuclear microprobe facility

The NAC NMP facility is discussed, showing that it is a well characterised analytical tool, and some novel features are incorporated, such as on-demand beam deflection and a new lid for the sample chamber.

Biological applications of the NAC nuclear microprobe

The nuclear microprobe (NMP) is an established analytical instrument for the determination of minor and trace elements. It allows measurements with a spatial resolution of the order of 1 μm and minimum detection limits down to few ppm by weight, with excellent scanning capabilities. The nuclear microprobe of the National Accelerator Centre, South Africa, is being used in a wide number of applications in the biosciences. The complementarity of proton-induced x-ray emission and backscattering spectrometry in a wide range of biological applications is shown. The advantages and restrictions of true elemental imaging are also discussed.

Investigation of Ni hyperaccumulation by true elemental imaging

Abstract The newly implemented Dynamic Analysis method for on-line elemental imaging was used to study Ni hyperaccumulation in Senecio coronatus (Thunb.) Harv. Asteraceae, one of only nine Ni hyperaccumulating plants found in the African continent. Elemental maps were obtained from samples with thicknesses varying from 0.4 to 5 mg/cm 2 by assuming cellulose (C 6 H 10 O 5 ) as constant matrix composition for the whole scanned area. The agreement between point analyses and results inferred from maps is good for small thickness variations within scanned regions. Maps of very inhomogeneous samples require a more time-consuming approach of thickness corrections in every pixel.

Quantitative micro-PIXE comparison of elemental distribution in Ni-hyperaccumulating and non-accumulating genotypes of Senecio coronatus

The Ni hyperaccumulator, plant species Senecio coronatus (Thunb.) Harv., Asteraceae is an example of plant adaptation mechanisms to different ecological conditions. This widespread species can inter alia be found on serpentine outcrops and the genotypes growing in serpentine soils show different ways of adaptation. The populations from two distant localities take up and translocate Ni in concentrations which are normally phytotoxic, while plants growing on a different site, in the vicinity of another hyperaccumulating species, absorb amounts which are typical for most of the plants found on serpentine soils. The NAC nuclear microprobe was used to compare the distribution of Ni and other elements in selected organs and cells with simultaneous use of PIXE and proton BackScattering (BS). Quantitative maps of stems showed large differences in concentrations and distributions of major and trace elements. In hyperaccumulating genotypes Ni is present everywhere within stem tissues, but the highest concentrations were found in the epidermis, cortex and phloem. In non-accumulating plants Ni was concentrated in the phloem. In the leaf epidermis Ni was concentrated in the cell walls for both accumulating and non-accumulating plants. These results suggest that biochemical diversity is more than morphological, because investigated genotypes belong to the same taxon.

Botanical applications in nuclear microscopy

Abstract An overview of botanical applications in the field of nuclear microscopy is presented. A wide range of applications has been studied up to now and included an array of very thin to thick samples. The relevant methods of sample preparation which are critical to many botanical applications are discussed. Quantitative mapping techniques allowing simultaneous quantitative studies of major and trace elements offer exciting possibilities in various fields of application, from science to industry and agriculture. In these studies PIXE and RBS were typically used to obtain complementary information. Recent examples are presented.

A PIXE study of abnormal X-rays from binary fluorides with protons in the range 0.4–2 MeV

Previously reported abnormally high X-ray yields from the fluorides of some transition metals were confirmed. Using proton beams and beams of the molecule-ion 1H2+, at equivalent proton energies between 400 and 2000 keV the conditions for the production of abnormally high X-ray yields were studied for the effect of ion beam energy, beam current, charge, target thickness and atomic number of the target metal. The effect was probably due to buildup of potential and discharge with the production of a flux of energetic electrons, with an energy distribution peaking above 10 keV.

Ion beam analysis for the determination of cation ratios as a means of dating Southern African rock varnishes

Abstract Stone artefacts found on the surface over much of the arid areas of Southern Africa are often covered with a rock varnish, the trace element composition of which has been analyzed by particle-induced X-ray emission (PIXE) and particle-induced gamma-ray emission (PIGME). Because Ti deposited in the varnish is less soluble and mobile, substitution of alkali metals by Ti served as a basis for dating. An experimental relationship was established between the “cation ratio” and the age of artefacts dated by more conventional means. This relationship provides a cation leaching curve from which undated samples can be dated by their cation ratios.

Development of a single ion irradiation system at CENBG for applications in radiation biology

Abstract A single event facility is currently under development at CENBG for applications in radiation biology. The aim is to induce the response of living cells by hitting selected individual specimens or specific sub-cellular compartments with an exact number of light ions. In order to avoid the construction of a complete beam line, it was decided to adapt the existing microprobe system. The line has been equipped with a removable final irradiation stage constituting a versatile system working on demand either in external beam mode or classical analysis under vacuum. The beam blanking is ensured by particle detectors which have been specifically designed to control MeV proton or alpha beams in a single event mode. This paper presents the overall experimental setup and first in-air experimental tests.

Cation-ratio differences in rock patina on hornfels and chalcedony using thick target PIXE

Abstract The ratio of (K + Ca) to Ti in patina layers is time-dependent and decreases with age. Patinas on hornfels and chalcedony artefacts were irradiated by 2 MeV 4He+ ions and analysed by Rutherford backscattering and PIXE simultaneously. The patinas on hornfels and basalt showed a self-consistent variation of cation-ratio with typological age up to 128000 years B.P., but the rate of growth was apparently slower on chalcedony.

Micro-analysis of kidney stones sequentially excreted from a single patient

Abstract Eight kidney stones obtained from a single patient over a period of about eleven years were analysed in its natural form by Rutherford backscattering with 2 MeV 4 He + ions, PIXE with 3 MeV protons, and PIGE with 4.5 MeV protons using the newly installed nuclear microprobe at Faure. Since the mechanism of kidney stone nucleation and growth is still poorly understood, it was of interest to establish whether kidney stones from a single patient were constant in composition as regards trace element content and whether the type of stone is reproduced on new stones grown after the removal of existing stones. As expected, the stones were rich in Ca. The matrix was calcium oxalate. Light elements present in minor concentrations were P, S, Cl and K. Trace elements were in very low concentrations, and the presence of Fe, Ni, Cu, Zn, Se, Br, Rb, Sr and Pb were recorded. Trace element trends in the stones, analysed with micro beams were identified. A good positive correlation between Sr and Zn was observed.