B. Raith

Determination of lateral trace element distributions with the bochum proton microprobe

Abstract For a spatially resolved analysis of element distributions in inhomogeneous samples by means of PIXE, we equipped our microprobe with a scanning and data-handling system based on a PDP 11/44 computer with CAMAC interface. This system is capable of program-controlled beam movement on the target surface, in order to follow the optimum scan path required for the analysis of a certain type of sample. X-ray events are processed with respect to the actual beam position. Element distributions can be determined on-line by selecting software single channels, or — in order not to lose any of the information supplied by the experiment — all X-ray events together with the actual beam position can be stored in list mode on magnetic tape. This enables us to perform off-line analysis of the data with more sophisticated programs. The most significant features of our scanning and data-handling system will be described; its advantages will be demonstrated by measurements on biological samples.

Trace element detection sensitivity in PIXE analysis by means of an external proton beam

A systematic investigation of the detection sensitivities achievable for PIXE analysis by means of an external proton beam is described. Six different metal foils were used as exit windows. The X-ray background spectra were measured for the bombardment of thin carbon foils with protons of four different energies. From these measurements we calculated the minimum detection limits using experimentally determined ionization cross sections. Simultaneously γ-ray spectra were used to elucidate the higher-energy background in the X-ray spectra. Two examples of application are given to demonstrate our results regarding detection sensitivity.

Trace element analysis by ion induced X-ray emission spectroscopy☆

Abstract K and L X-ray emission rates for 37 elements and continuous background radiation from a thin carbon matrix produced by bombardment with protons of 1.5, 2, 3, and 4 MeV have been investigated. K-shell ionization cross sections for 25 elements for 2 MeV proton bombardment, minimum detection limits through the periodic system in the ppm range and optimum proton energies for highest sensitivity for a given element have been extracted from these measurements. 16O-ions turn out to be much less sensitive than protons of the same velocity. Two examples of applications to mineralogical and environmental problems are given.

PIXE analysis by means of an external proton beam

Abstract To optimize PIXE analysis by means of an external proton beam we determined the minimum detection limits for 14 different exit foils. Influences of geometrical parameters were investigated. One important result of our measurements is that the continuous background yields are nearly independent of the matrix thickness. On that account analysis of thick samples is indispensable for obtaining highest relative detection sensitivity. To evaluate actual concentrations from measured X-ray spectra of thick samples we imagine the samples to consist of thin layers so that the X-ray yields can be computed numerically. The ionization cross-section data used in these calculations are theoretically as well as experimentally determined values. Examples of the application of this technique to the analysis of metals and to the analysis of water, making use of appropriate preconcentration methods are shown.

PIXE analysis of environmental and biological samples using a proton microprobe

Abstract For the investigation of environmental and biological samples a proton microprobe has been built up at the Bochum Dynamitron Tandem Laboratory. By several improvements of the apparatus, e.g. optimization of the focal lengths and fine adjustment of the quadrupole lenses according to the results of a detailed beam transport calculation the beam diameter has been reduced to 6 μm fwhm. This device is used to measure lateral distributions of trace elements with Z > 15 in thin samples by means of PIXE. This technique has been applied to environmental and biological samples. An impactor sample has been investigated in order to test PIXE trace element measurements performed with a standard accelerator beam. In the field of biological samples our investigations concern the level of cooperative cellular colonies. Proceeding from a microphoto of a thin sample of human skin the element content in the region of interest has been determined by scanning.

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.

Measurements of mineralization process in the femur growth plate and rib cartilage of the mouse using pixe in combination with a proton microprobe

SummaryThe femoral bone from the 18-day pregnancy embryo and an rib cartilage of mature mice have been investigated using PIXE (proton induced X-ray emission) in combination with a proton microprobe on snap frozen cryosectioned material. The localization and the results of quantitative measurement of P, S, Cl, K, Ca, Fe and Zn have been correlated with the histochemical localization of inorganic deposits. It has been found that in calcifying and degenerating cartilage of the growth plate there is substantial loss of S; this element being indicative for sulphate groups of glycosaminoglycans. This change seems to be an important factor conditioning the process of mineralization. Zn is found in higher concentration in mineralized tissues, both in embryonal and mature cartilage as well as in the bone, and this suggests that Zn is also involved in the mineralization process. The mineralization of rib cartilage exceeds that of embryonal bone, and the Ca/P ratio is higher in the former than in the hydroxyapatite of the latter. The method described is a useful analytical tool especially for such types of studies in which elements are not easily redistributed by freezing, cutting and drying; e.g. in investigations of mineral deposits.

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%).

Beitrag zur Prparation von Spurenkonzentrat-Targets fr die PIXE-Multielementanalyse@@@Contribution to the preparation of trace concentrate targets for PIXE multi element analysis: Teil I. Grundlagen

SummaryA procedure is described for the preparation of trace concentrate targets for a multi-element determination by proton induced X-ray emission spectroscopy (PIXE). Traces such as Ag, Bi, Cd, Co, Cu, Fe, Hg, In, Mn, Ni, Pb, Pd, Tl and Zn are preconcentrated as diethyldithiocarbamidate chelates by use of a collector precipitation. The target in this procedure is a membrane filter with the separated collector layer which is fixed to an acrylic glass support. The target materials were selected with regard to extremely low blanks. As collector element molybdenum is used, whose X-ray signals cause no measurable disturbances on the trace determination and which simultaneously serves as an internal standard to correct irregularities in the thickness of the collector layer. The recoveries of most of the investigated elements are > 95%; the relative standard deviation of the complete analytical procedure is smaller than 10%. Depending on the element, the limit of detection (3 σ) was found to vary between 0.05 and 1 μg regarded to the whole target. The accuracy of the method was verified by independent determination methods using models of water samples.ZusammenfassungEs wird ein Verfahren zur Präparation von Spurenkonzentrat-Targets für die Multi-Elementbestimmung durch protoneninduzierte Röntgenemissions-Spektrometrie (PIXE) beschrieben. Dazu werden die Spuren Ag, Bi, Cd, Co, Cu, Fe, Hg, In, Mn, Ni, Pb, Pd, Tl und Zn als Diethyldithiocarbamidat-Chelate mit Hilfe einer Kollektor-Fällung angereichert. Target ist ein auf einer Plexiglas-Unterlage fixiertes Membranfilter mit der abfiltrierten Kollektorschicht. Die Targetmaterialien wurden im Hinblick auf eine möglichst geringe Blindwertbelastung ausgesucht. Als Kollektorelement wird Molybdän verwendet, dessen Röntgenlinien die Bestimmung der Spuren nicht stören und das zugleich als innerer Standard zur Korrektur von Ungleichmäßigkeiten in der Dicke der Kollektorschicht dient. Die Anreicherungsausbeuten der Mehrzahl der eingesetzten Elemente ist > 95%; die relative Standardabweichung des vollständigen Verbundverfahrens liegt unter 10 %. Es wurden Nachweisgrenzen (3 σ) ermittelt, die — je nach Element — zwischen 0,05 und 1 μg pro Target liegen. Die Richtigkeit des Verfahrens wurde an wäßrigen Modell-Analysenproben mit Hilfe unabhängiger Verfahren sichergestellt.SummaryUsing drinking water, optical glass and blood as sample materials the applicability of the earlier described method [2] for the preparation of trace concentrate targets was proved. The accuracy of the analytical results obtained by PIXE was verified by AAS.ZusammenfassungAnhand einiger Beispiele (Trinkwasser, optisches Glas, Blut) wird die Anwendbarkeit der früher beschriebenen Methode [2] zur Präparation von Spurenkonzentrat-Targets nachgewiesen. Die Richtigkeit der durch PIXE gewonnenen Analysendaten wurde durch AAS überprüft.

The analysis of mineral deposits and proteoglycans content in the cartilage of mouse trachea using PIXE in combination with proton microprobe

The tracheal cartilage of mature mice have been investigated using PIXE (proton induced X-ray emission) in combination with a proton microprobe on snap frozen cryosectioned material. The localization and quantitative measurements of P, S, Cl, K, Ca, Fe, and Zn concentrations as well as direct and indirect assessment of glycosaminoglycans by measurement of S content and measurement of bound colloidal iron at pH = 1.8 has been performed. Adjacent sections were stained with the Hale method in Müller modifications and the v. Koss method for sulphated mucins and inorganic deposits respectively. It has been found that hyaline cartilage in trachea contains mineral deposits and that P + Ca amounts up to 22% of cartilage dry mass. The Ca/P ratio approaches 2 what indicates hydroxyapatite type crystals. The cartilage contains substantial amounts of S reflecting the presence of sulphate groups. It was found that the cartilage binds also colloidal iron at low pH. There is a good correlation between places with high amount of bound colloidal iron assessed by PIXE and places showing strong Prussian Blue staining. The Fe/S ratio was, however, much lower in the cartilage than in other tissues what indicates that the colloidal iron method does not give quantitative results. There were no regions showing substantial decrease in Fe/S ratio which we found previously as typical for degenerating and calcifying growth plate cartilage. This may be connected with a relatively low degree of calcification degree of the tracheal cartilage.