S. Divoux

Comparison of different excitation methods for X-ray spectral analysis

ZusammenfassungDie verschiedenen Anregungsmethoden der Röntgenspektralanalyse mit Protonen, Photonen und Elektronen (PIXE, XRFA bzw. EPMA) werden hinsichtlich ihres Nachweisvermögens, ihrer Präzision und Genauigkeit verglichen. Die Beurteilung der jeweils optimierten Anregungsmethoden basiert auf praktischen Problemen der Spurenanalyse: auf der Analyse von Aluminium, von Blei und von Spurenkonzentraten aus Wasser und Glas. Für dicke homogene Proben erwies sich die XRFA wegen der sehr guten Stabilität der heutigen Geräte als überlegen. PIXE ist vorteilhaft anzuwenden, wenn dünne Proben vorliegen oder wenn eine Probenvorbereitung, wie z.B. eine chemische Voranreicherung, erforderlich ist, die zu einer zusätzlichen Streuung von ⩾ 1% führt, so daβ die hohe Stabilität der XRFA-Geräte nicht mehr zum Tragen kommt. EPMA ist sowohl PIXE als auch XRFA unterlegen, solange nicht die lokale Verteilung von Elementen zu ermitteln ist.SummaryThe different excitation methods of X-ray spectral analysis with protons, photons and electrons (PIXE, XRFA and EPMA, respectively) are compared with regard to detection power, precision and accuracy. The evaluation of the independently optimized excitation methods is based on practical problems of trace-analysis: on the analysis of aluminium, lead and trace-concentrate targets of water and glass. For thick homogeneous samples XRFA turned out to be the best method, because of the very high stability of modern instruments. PIXE is advantageous for thin samples and if some kind of sample preparation like chemical preconcentration is necessary which introduces an additional scatter of ⩾ 1%, so that the high stability of XRFA instruments is no longer effective. EPMA is inferior to both, PIXE and XRFA, in all cases, where information on the lateral distribution of the elements is of no interest.

K-shell ionisation of heavy target elements (42 ⩽ ZT ⩽ 62) bombarded with protons in the energy range 0.5 MeV–6 MeV

Abstract Total K-shell ionisation cross sections were measured for the irradiation of thin solid targets ( μg cm 2 ) of 92 Mo, 104 Pd, 120 Sn, 138 Ba, 140 Ce, 1142 Nd and 144 Sm with protons of 0.5 MeV u ⩽ E Lab M Proj ⩽ 6.0 MeV u . Only isotopes were chosen as targets for which internal conversion of de-exciting transitions of nuclear excited states does not contribute to K-shell ionisation. The measured cross sections are compared with theoretical calculations within the framework of the perturbed-stationary state theory and with calculations based on the semiclassical approximation. Only for very low proton energies ( ξ ⩽ 0.25) are there systematic differences between the experimental data and the theoretical calculations; for ξ > 0.25 most of the measured ionisation cross sections agree with both calculations within the experimental errors (9–15%).

Calcification of the aortic wall in hypercalcemic rabbits.

The mineralization process was investigated in the aortic wall of hypercalcemic rabbits. The elevated calcium level in serum was induced by intramuscular injection of vitamin D3. The animals were killed at different times of the experiment (max. 246 d). The freeze-dried tissue homogenates were used for elemental composition studies by means of proton induced X-ray emission (PIXE) and atomic absorption spectroscopy. The structural information was obtained from infrared (IR) and X-ray diffraction (XRD) spectra. Moreover, the ascending part of the aortic arch was separated and used for micro-PIXE (PIXE in combination with proton microprobe) and histochemical examinations. It was found that hypercalcemia (blood serum Ca content elevated by about 20%) induced calcification of the aortic wall. The mineral phase within the aortic wall consisted of Ca-P salts. The Ca/P ratio continuously increased during the experiment and approached 2 after 246 d of the vitamin D3 treatment. The IR and XRD studies made possible the identification of the complex phase composition of the samples. The hydroxyapatite crystals were detected after 196 days, however, in earlier phases of the experiment, amorphous calcium phosphate, dicalcium phosphate dihydrate and octacalcium phosphate were also observed. On the basis of the data obtained, the mechanism of the precipitation and growth of inorganic deposits in the tunica media of the aortic wall was discussed.

Intramembranaceous ossification analyses by a proton microprobe.

SummaryThe proton induced X-ray emission method in combination with a proton microprobe was applied to study the intramembranaceous ossification. As material sections of mouse embryo skulls from the 17th and 19th day of gestation were used. The morphology of the sample was examined by routine histochemical procedure performed on the sections adjacent to that irradiated by the proton microprobe. The measurements were made in line scan and raster scan mode. The concentrations of P, S, Cl, K, Ca, Fe and Zn were determined at each irradiated point. The average element concentrations were calculated for four parts of each section (bone, cartilage, mesenchymal tissue close to the bone and mesenchymal tissue in other places). The distributions of Ca and P (less markedly than Ca) concentrations almost exclusively correlate with localization of the bone while S, Cl and K concentrations show preference to the cartilage. The amount of inorganic material in flat bones of the 17-day embryo amounts to 14% of the dry mass. The material is characterized by a Ca/P ratio of bout 1.6 In the embryo 2 days older the amount of the inorganic phase is practically the same (15%) while the Ca/P ratio approaches 2. This suggests the presence of the precursor phase in the flat bone calcification. It is possible that octacalcium phosphate (Ca/P ratio equals to 1.72) is formed at the onset of the flat bone mineralization which transforms rapidly (in 2 days) to a more stable mineral (defective hydroxyapatite).

STUDY OF ELEMENT PROFILES IN ARTIFICIALLY WEATHERED STONE SAMPLES BY PROTON-MICROPROBE ANALYSIS

Summary A proton microprobe was applied to the determination of chemical alterations in artificially exposed stone samples. Proton Induced X-ray Emission (PIXE) spectrometry as a multielement technique enabled high spatial resolution measurements of the distribution of Si, S, K, Ca, Ti and Fe in the examined stone materials, which were sandstones, sandy limestones and limestones. Analyses were performed on the cross sections of SO 2 -exposed samples using an apparatus arrangement which allowed the measurement of the proton-beam current during sample irradiation. As a result, the absolute values of the X-ray intensities could be determined and a calibration with standards became possible

Micro-PIXE quantification of histochemical reactions

Abstract The proton induced X-ray emission in combination with a proton microprobe (micro-PIXE) was used for the quantitative determination of a locally bound histochemical reaction end-product. The determination of proteoglycans (PG) content in the cartilage is described in detail. The cartilage from the femur and the skull of 17–19 days old embryos and from ribs of mature CBA strain mice was investigated. The 8 μm cryomicrotome sections, placed on a formvar backing, were incubated in colloidal iron or in alcian blue (dye molecule contains Cu) solutions. The determination of PG contents was made indirectly by assessment of the Fe or Cu concentrations. Differences in the PG contents were observed within all investigated cartilage types. The embryonal cartilage contains more PG than that obtained from mature animals. For the cartilage from the femur the highest content of PG was found in the mineralization front while fully formed bone trabeculae exhibited a PG level 10 times lower. In the case of intramembranaceous ossification the content of PG was also higher in the skull cartilage than in the loose connective tissue. On the basis of the performed studies some methodological conclusions can be drawn. For PG determination, the alcian blue method is more reliable than the colloidal iron technique. The review of the histochemical procedures which may be combined with the micro-PIXE method is also given.

Trace preconcentration for PIXE multi-element analysis

Abstract A procedure for the preparation of trace concentrate targets for a multi-element determination by PIXE spectrometry is described. Collector precipitations with chelating reagents and subsequent membrane filtration were used for the preconcentration of the trace elements, leading to a sample target which can directly be analysed by PIXE spectrometry with an external proton beam. Different collector elements and chelating reagents were tested to optimise the preconcentration procedure for the analysis of water and optical glass.

Proton microprobe studies of the mineralization process in selected organic matrices

Abstract The application of the proton-induced X-ray emission method in combination with a proton microprobe (micro-PIXE) to studies of the mineralization process in selected organic matrices is presented. The flat-bone mineralization of the skull of 17–19 days pregnancy mouse embryos is described in detail. The section thickness as well as concentrations of P, S, Cl, K, Ca, Zn and Br were determined using the raster- or line-scan irradiation mode. On the basis of Ca and P contents the amount of inorganic phase was determined for each sample under investigation, while the Ca/P ratio was used for the identification of the chemical compounds within inorganic material. In the embryonal bones we observed almost stoichiometric hydroxyapatite; however, in the intramembranaceous ossification of the young (17 day) animals, octacalcium phosphate was identified. At the given age of the embryo the amount of minerals is much higher in the femur bone than in flat bone. The micro-PIXE method furthermore turned out to be sensitive enough to study the mineralization accompanying malignant tumors. We have also observed the involvement of some trace elements in the development of the mineralization process. The last two observations are unattainable by histological staining.