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ELEMENTAL MICROANALYSIS IN BOTANY: NUCLEAR MICROPROBE AND COMPETING METHODS
W.J. PRZYBYLOWICZ* and J. MESJASZ-PRZYBYLOWICZ, Materials Research Group, National Accelerator Centre, P.O. Box 72, 7131 Faure, South Africa
Botany is one of the research disciplines where microanalytical analysis of minor and trace elements can substantially contribute to the existing knowledge and to the results obtained
using a more classical methods. This applies to solving problems in research areas such as plant physiology, agriculture and environmental pollution. An overview of recent applications is presented. Special emphasis is made on an update of nuclear microprobe applications, following earlier review on that subject [1]. Problems solved using other microanalytical techniques such as EDX, SIMS, LMMS, SXRFM and EELS are also reported. Quantitative capabilities of each method, including quantitative mapping, are reviewed. Proper methods of specimen preparation are described and discussed.
[1] W.J. Przybylowicz, J. Mesjasz-Przybylowicz, V.M. Prozesky and C.A. Pineda, Nucl.
Instr. Meth. B 130 (1997) 335.
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MANGANESE PROFILES IN FRESHWATER MUSSEL SHELLS
R. Siegele, D.D. Cohen, S.J. Markich and R.A. Jeffree, Australian Nuclear Science and Technology Organisation, PMB 1, Menai 2234, NSW, Australia.
The pollution of the marine environment and rivers is of growing concern, however many pollution events, particularly in remote areas, remain undetected. Bones and shells of organisms living in the aquatic environments can be used as monitors for both contemporary and historical pollution events. In order to use these records, various factors such as patterns of bioaccumulation over the life span of the animal need to be understood.
Ion microprobes offer a tool to measure metal (impurities) at very low concentrations with a high lateral resolution. This paper describes the use of the heavy ion microprobe at ANSTO to measure Mn profiles in freshwater mussel shells. The ANSTO heavy ion microprobe can focus 9 MeV He, 25 MeV C as well as 35 MeV Cl ions to spot sizes down to 5u.m. With the microprobe manganese profiles across mussel shells were taken after 10 days exposure of the shells to increased Mn concentrations in the water, in order to determine the pattern of accumulation in the shells. Additionally 2-dimensional imaging was used to investigate the accumulation of trace elements in particular areas.
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WEATHERING AND METAMICTIZATION OF ZIRCON : NEW CONSTRAINTS FROM MICRO-PROBE MEASUREMENTS.
E. Balan' P. TroceUier2, D. Neuville3, J.-P. Muller1'4 and G. Calas1
1 Laboratoire de Minéralogie-Cristallographie UMR 7590, CNRS, Universités Paris 6 et 7 and IPGP, Case 115, 4 Place Jussieu, 75252 Paris Cedex 05, France, 2 CEA - CNRS, Laboratoire Pierre Sue, Centre d'Etudes de Saclay, 91191 Gif sur Yvette Cedex, France, 3 Laboratoire de Géomatériaux IPGP, 4 Place Jussieu, 75252 Paris Cedex 05, France, 4IRD, 213 rue Lafayette, 75480 Paris cedex 10, France.
Zircon (tetragonal ZrSiO4) is the oldest mineral found at the Earth's surface. Its resistance to dissolution is exceptional compared to that of other silicate minerals. Because of this important property, zircon is widely used in tracing and dating geological processes and it is considered as potential waste matrix for the plutonium. However, zircon may loose its resistance in some environments (hydrothermal fluids, tropical soils) and the use of zirconium as an immobile element in weathering processes has been questioned. In addition, metamictization, i.e. the loss of crystal periodicity due to the accumulation of radiation induced defects, strongly modifies the properties of zircon.
Surprisingly, little attention has been paid on the role of metamictization on the weatherability of zircon in natural environments. Here, we report new results obtained on zircons sampled in the sediments and the soils of the Amazonian Basin (Brazil). These zircons originate from the Precambrian Guyana shield (0.5-3 Ga). Their actinide (U, Th) concentrations were determined between 10-7000 ppm by proton induced X-ray emission (PIXE) micro-analysis.
This range of concentration is consistent with that commonly reported for crustal zircons.
Thus, the studied series can be regarded as representative. Their metamictization degree, expressed as a radiation dose and determined by Raman micro-probe, is between 5.1014 --3.1015 alpha-decay/mg. The maximum degree of metamictization coincides with the degree for which radiation damages become predominant. It is also significantly lower than that expected for the more actinide enriched zircons. This strongly suggests that more damaged zircon disappeared during weathering processes. Otherwise, for the observed metamictization range, the soil formation does not appear to affect the zircon population. Since Rutherford backscattering (RBS) measurements shows that no protective Zr-enriched layer forms at the surface of these zircons, their resistance to weathering can be attributed to the zircon crystal structure.Consequently, our results suggest that metamictization has a major control on zircon weathering at the Earth's surface.
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NUCLEAR MICROPROBE ANALYSIS OF LICHEN SURFACES
Brett M. CLARK. Nolan F. MANGELSON, Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.
Larry L. ST. CLAIR, Department of Botany and Range Science, Brigham Young University, Provo, UT, 84602, USA.
Lawrence B. REES, Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602, USA
Patrick G. GRANT, and G. S. BENCH, Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
Elemental analysis of upper and lower cortical surfaces of the lichen Xanthoparmelia chlorochroa have been performed using microbeam proton induced x-ray emission (PDCE).
The analyses demonstrate that element distribution patterns on lichen surfaces are heterogeneous and complex. The unique characteristics of lichens present some interesting analytical challenges that will be addressed. The abundance of inorganic particles and diversity in particle size and composition confirm the long-standing hypothesis that paniculate entrapment and decomposition is a primary mechanism for nutrient accumulation employed by lichens. The implications of this paniculate study to the role of lichens as biomonitors of air pollution will also be discussed.
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CHARACTERISATION OF ZINC IN A DREDGED SEDIMENT DEPOSIT AND IN THE SUBSOIL BY COUPLING jiPIXE, jiRBS, AND jiEXAFS
MP Isaure1-2. A Laboudigue1, A Manceau2, C Tiffreau1, P Trocellier3
1- Centre National de Recherche sur les Sites et Sols Pollués, BP 537, 59505 Douai Cedex France,
2- Environmental Geochemistry Group, LGIT-IRIGM, University of Grenoble, BP53, 38041 Grenoble, Cedex 9, France
3- CEA-CNRS, Laboratoire Pierre Sue, CE Saclay, 91191 Gif sur Yvette, Cedex, France
In flat lands, sediments deposited in ship-canals are periodically dredged for maintenance and are generally disposed on agricultural soils along banks. In industrial areas, the canal sediments are often polluted by heavy metals and these practices are hazardous because toxic metals can migrate to the underlying soil and groundwater. The chemical risk depends on the mobility and bioavailability of metals, which themselves depend on their speciation.
The aim of this study is (i) to identify the speciation of zinc in a contaminated dredged sediment (6000 ppm of zinc) collected in a highly polluted area in the North of France, (ii) to determine which particular Zn-containing mineral species are able to release zinc from the sediment to the non polluted subsoil, and (iii) to identify the mechanisms of Zn immobilisation in the subsoil. Owing to the highly heterogeneous nature of sediment and soil, bulk analyses should be completed by investigations at the micron scale. nPIXE and yRBS are well adapted to our study because (i) uPIXE gives information on the spatial distribution of elements with Z>12, (ii) uRBS allows to obtain the distribution of the elements with depth of the sample, with a good selectivity for thin heavy element layers deposited on light matrix (iii) both techniques present multielemental analytical capabilities and high sensitivity.
uEXAFS allows to obtain structural information on micron-scale particles.
Coarse particles of the sediment (500-2000 |iin) contain high amount of zinc (-1.5%) and were studied by uPIXE and uRBS. uRBS results showed that Zn, Fe and S are concentrated at the surface of the grains and uPIXE elemental maps allowed to identify an association between Zn and S, irregularly distributed on the particles. Sometimes, Fe is associated with S and Zn. Sphalerite (ZnS) was identified by uEXAFS as the major Zn-bearing phase.
After 18 months of deposit, the zinc concentration in the subsoil increased from originally -70 ppm to ~ 300 ppm. This enrichment at least partly results from a direct transfer of particles from the sediment to the soil, but a migration of dissolved Zn, released by the weathering of ZnS, followed by its immobilisation in neoformed phases can not be excluded. uPIXE, uRBS and pEXAFS experiments are in progress to distinguish the transferred particles from the neoformed phases.