Dynamic secondary ion mass spectrometry (SIMS) has been utilised to study the post-mortem distribution of aluminium in air-dried frozen sections from unfixed, unstained human brain in order to minimise contamination of the tissue and avoid redistribution and extraction of endogenous tissue aluminium. Substrates, sputter-coated with silver, were found to be free of focal aluminum surface contamination and thus minimised substrate induced artefacts in the tissue aluminium ion image. SIMS imaging of aluminium secondary ions at a mass resolution that eliminated the major molecular interferences, combined with a photomontage technique provided a unique strategy for studying aluminium distribution in tissue unrivalled by other spatially resolved microanalytical techniques such as laser microprobe mass spectrometry or X-ray microanalysis. Using this strategy, high densities of focal aluminium accumulations have been demonstrated in the cerebral cortex of the majority of chronic renal dialysis patients studied. In contrast, such aluminium accumulations were absent in control patients. SIMS imaging of aluminium appeared to provide much better discrimination between the dialysis patient group and the control group than one of the most widely used techniques for measuring aluminium in bulk samples, graphite furnace atomic absorption spectrometry. Preliminary studies have shown the feasibility of quantifying focal aluminium SIMS images obtained from brain tissue using aluminium-loaded brain homogenates as reference standards.
The use of advanced surface-analytical techniques t o study the sorption of the actinides uranium and plutonium on to rocks and their consistuent minerals, in the context of radioactive waste disposal, is described. Nuclear microprobe analysis was used t o quantify the extent of sorption of actinides via Rutherford back-scattering (RBS); data on the minerals o n which sorption had occurred were provided by particleinduced X-ray emission. Both surface and su b-surface concentrations of actinides were measurable. Secondary-ion mass spectrometry (SIMS) was used to measure qualitatively the distribution of sorbed actinides and their penetration rates into minerals. The equipment used at Harwell is described. Complementary use of both techniques in parallel is highly advantageous; RBS is used to quantify actinide surface loadings, w i t h limited lateral and depth resolution, but, allied to SIMS, which has excellent spatial resolution, samples can be analysed both quantitatively and with high spatial resolution. Concentrations of uranium and plutonium sorbed o n t o minerals can be routinely determined w i t h sensitivities d o w n to 1 ng cm-*. The data obtained are used to identify the minerals in a rock that are important for actinide sorption.
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