J. Takacs

The Oxford 1 μm proton microprobe

Abstract The coupled triplet configuration of the Oxford microprobe system in which spatial resolutions of 1 μm have been achieved is described together with the hardware, data collection and operation of the probe. Using the microprobe in conjunction with the technique of PIXE, two-dimensional elemental maps of mouse macrophages have been constructed and elemental concentrations down to 2×10 −17 g/μm 2 have been measured. Measurement of the iron content of the mouse cells indicates that the proton probe is capable of detecting an increase in iron within the cell after the cytoskeleton has been labelled by immunocytochemical means. Limitations in the technique of microprobe PIXE with respect to cellular biology are briefly discussed.

Distribution of elements in the Lily pollen tube tip, determined with the Oxford scanning proton microprobe

SummaryPollen tubes ofLilium longiflorum were fixed with glutaraldehyde and investigated unsectioned with the Oxford scanning proton microprobe (SPM). Two-dimensional maps which show the distribution and concentration of phosphorus, sulphur, chlorine, potassium, calcium, iron, copper, zinc and arsenic are presented. The maps show that, within the pollen tube tip region, calcium and zinc exhibit relatively steep longitudinal concentration gradients compared to the more flat distributions of phosphorus and sulphur. Chlorine, potassium, iron and copper appear equally distributed along the tube. All elements with the expception of arsenic show the highest concentration within the cell protoplasm and not in the cell wall. Additional signals of arsenic, chlorine and potassium originate from the remaining fixative dried around the tube, containing also the free ions of the cell. The arsenic signals originate exclusively from the buffer used during fixation. The different maps are compared and discussed in relation to their significance to the pollen tubes.

A scanning proton microprobe study of macrohairs from the lemma of the grass Phalaris canariensis L

Proton-induced X-ray emission combined with a scanning proton microprobe has been used to investigate the distribution of inorganic elements in silicifying macrohairs from the lemma of the grass Phalaris canariensis L. Results, presented in the form of X-ray spectra and two-dimensional elemental maps, showed that the inorganic elements Si, K, P, S and Cl were spatially organized within the macrohairs during the different stages of silicification. Much lower quantities of all elements except silicon were found in the mature macrohairs. It is suggested that these changes in the inorganic content of the macrohairs are related to a silicification process that is associated with cellular activity.

REAL AND PARASITIC ABERRATIONS OF QUADRUPOLE PROBE-FORMING SYSTEMS

Abstract The aberrations which affect the performance of magnetic quadrupole probe-forming systems are discussed. The methods of calculating these are reviewed and calculations using the Oxford computer program (OXRAY) are compared with experiment. Finally the real (chromatic and spherical) and parasitic (rotational misalignment etc.) aberrations of some existing microprobes are calculated and their relative effects examined.

HEPATIC COPPER DISTRIBUTION IN PRIMARY BILIARY-CIRRHOSIS SHOWN BY THE SCANNING PROTON MICROPROBE

A number of conditions are associated with abnormalities of trace metal handling by the liver. We report the application of the Oxford scanning proton microprobe to the analysis of hepatic copper in one such condition, primary biliary cirrhosis. The scanning proton microprobe analyses conventional tissue sections (5-10 micron thickness) and produces simultaneous elemental distribution maps of biologically relevant elements with a spatial resolution of 1 micron and a detection limit better than 1 ppm. We have confirmed the localisation of excess copper to periportal areas and suggest that such accumulation is confined to a proportion of periportal hepatocytes. We have also shown a close spatial correlation between regions of copper accumulation and areas of high sulphur concentration. The copper to sulphur ratio in these areas is consistent with their identity as aggregates of copper loaded metallothionein, and the scanning proton microprobe was further able to show that the aggregates contain less than 30 ppm zinc.

A wide area scanning system for the oxford proton microprobe

Abstract In order to fully exploit the analytical capabilities of the proton microprobe, it is desirable to be able to raster the focused beam over large areas of the target without loss of resolution. This paper describes the Oxford microprobe scanning system, which has some novel and interesting features. The beam spot is rastered over the sample using a fast vertical scan and a slow horizontal scan. The fast deflection is produced by two coils situated before the lens system, orientated so that the deflection occurs in the plane of minimum aberration. The slow deflection is achieved by unbalancing the currents in the coils of the last quadrupole in the focusing system. This has the effect of inducing a dipole field inside the lens, which causes the beam to be deflected with little increase in aberration. This system enables the beam to be rastered over areas from 20 μm × 20 μm to 4 mm × 4 mm. Calculations and experimental evidence indicate that for undeflected beam spot sizes of 1 μm × l μm, even for the 4 mm × 4 mm scans, the broadening at the extremities of the scan is no more than 10 μm.

THE OXFORD SCANNING PROTON MICROPROBE - A MEDICAL DIAGNOSTIC APPLICATION

Primary biliary cirrhosis (PBC) is a disease characterised by progressive destruction of small intrahepatic bile ducts, cholestasis, and high levels of copper within the liver. The Oxford 1 μm scanning proton microprobe (SPM) has been used to construct elemental maps of a 7 μm section of diseased liver at several different magnifications. The results of these investigations have shown that the copper is distributed in small deposits ( < 5 μm) at specific locations in the liver. Further there appears to be a 1:1 atomic correlation between copper and sulphur, indicating the presence of an inorganic salt or a protein with approximately equal numbers of copper and sulphur atoms.

Elemental mapping of human nervous tissue using the scanning proton microprobe

The scanning proton microprobe (SPM) is a powerful multi-elemental analytical instrument capable of elemental mapping at the parts per million level of sensitivity. In this report we demonstrate that the SPM is sufficiently sensitive and versatile to distinguish different regions of the human central nervous system on the basis of differences in their normal endogenous elemental composition.

Studies of 1s2s 3S-1s2p 3P transitions in helium-like Ne8+ recoil ions using photographic spectroscopy

This work describes the application of the technique of photographic VUV spectroscopy to accurate measurement of the wavelength of the theoretically interesting 1s2s 3S1-1s2p 3P2 transition in helium-like Ne8+ in a recoil ion source. Good resolution is obtained, and a preliminary value of 124.815±0.002 nm is found for the wavelength.

Modelling of Multiple Electrode Van de Graaff Generators with up-Charge and down-Charge Processes

Van de Graaff generators with multiple electrodes came about as a result of the demand for ever increasing voltages in various fields of science. The transient behaviour of these generators is mostly determined by their internal electrode arrangements. In the analysis given here these effects are divided into two categories; the effect of the column electrode structure and that caused by the large intermediate shields. The modelling shown here takes into consideration both effects and shows the way of analysing these high voltage generators with up to n internal electrodes. The results show the striking difference in behaviour of these generators with up-charge and down-charge processes. The numerical example given was based on one of the existing Vand de Graaff generators in Oxford.