Georges Weber

Thickness Variations and Lifetimes of Carbon Foils under Nitrogen-ion Bombardment

The deposition of carbon upon carbon foils and the lifetimes of foils during bombardment by nitrogen ions have been investigated under various experimental conditions. The rate of carbon deposition depends upon the energy and current density of the bombarding ions, as well as upon the condition of vacuum. For ion energies of 0.125-1.5 MeV/atom and current densities of 0.25-13.0 μA/cm2, increases in areal density of up to 40% for 10 μg/cm2 foils have been observed under conditions typically employed in nuclear physics and beam-foil spectroscopy. The source of the deposited carbon appears to be carbon-containing molecules in the residual gas of the vacuum system. Elimination of carbon deposition has been achieved by surrounding the foil with a cooled baffle. The lifetime of the foil (time until breakage) is found to be, at a given energy per atom, the time required for a constant number of atoms to have bombarded the foil.

Use of a variable incidence angle PIXE arrangement for studying pigment multilayers

Abstract Particle induced X-ray emission (PIXE) method is used in the field of archeometry and specially to investigate pigment colored multilayers. The tilting of the sample with respect to the incident proton beam direction allows to modify the relative contribution of each layer to the fluorescence signal. The experimental results coupled to computer simulations lead to semi-quantitative information about the thickness, the position and the composition of the successive layers.

Use of PIXE-PIGE under variable incident angle for ancient glass corrosion measurements

Abstract Although glass is usually considered as a very stable archaeological material, it can undergo severe degradation. Soda-lime glass, the most common glass throughout ancient times, is particularly sensitive to this problem. The glass surface absorbs moisture from its environment and the contact with CO 2 causes Na 2 O and NaOH to convert to Na 2 CO 3 , which is extremely hygroscopic. The subsequent unstable glass layer can be leached out and causes decomposition of the glass. The non-destructive PIGE–PIXE method of investigation allows detection of this phenomenon even if no visible effect appears. The variable incident angle method is able to discern the depth of the degradation. One aim of such studies is the possible dating or at least fake detecting of archaeological materials. Furthermore, even objects of large size can be investigated with the atmospheric PIGE–PIXE set-up. Some examples of measurements on ancient glass are given.

Distribution of Metals in Human Lung: Analysis by Particle Induced X-Ray Emission

Thirty-five lung pairs obtained during autopsy from randomly selected patients were investigated by particle induced X-ray emission for overall and regional elemental content determination. In each case the interbronchial lymph node was simultaneously processed. While homogenous distribution has been consistently observed for potassium, calcium, iron, copper, zinc, and rubidium, a very different distribution was recorded for titanium, chromium, nickel, and strontium. The significance of these results is discussed with regard to pollution hazards. Regional accumulation of this second group of elements seems to be related to air pollution peculiar to Liège. Advantages and limitations of the technique and the need for further research are stressed.

Fonction d'excitation de la réaction 12C(d,p0)13C entre 400 et 1350 keV — distributions angulaires

Abstract The excitation function of the 12 C(d,p 0 ) 13 C has been measured at θ = 150° for 400 to 1350 keV deuteron energy. The angular distribution has been measured from 80° up to 160°. These measurements have been performed in order to make possible the use of this reaction for superficial carbon determination by direct observation of the emitted protons.

Metal determination and quantification in biological material using particle-induced X-ray emission

Metal monitoring is one of the major concern of biological and biomedicine research. The particle-Induced X-ray emission (PIXE) method allows a sensitive, multi-elementary and non-destructive analysis of crude samples or purified molecules. A brief description of the method is presented and is followed by a short review of biological applications. The last part emphasises the interest in PIXE for metalloprotein analysis after denaturing and non-denaturing electrophoresis.

Biomedical application of PIXE in university of liege

Three biomedical applications of charged particle induced X-ray emission spectroscopy (PIXE) are outlined. The different fields investigated include biophysics (protein study), cancer chemotherapy (cis-dichlorodiamineplatinum (II) associated to liposomes as carriers) and lung pathology (serum and broncho-alveolar lavages). The samples were irradiated with 3 MeV protons (cyclotron) in a nitrogen atmosphere.

Study of color centers induced by PIXE irradiation

The particle induced X-ray emission method is perfectly adapted to the study, by external beam, of art objects (like paintings) and allows non-destructive analysis of the atomic composition of the target. However, a strange phenomenon occurs during irradiation on some pigments: dark brownish stains appear, and this could be due to the formation of color centers. In fact, these darkening spots progressively fade out and disappear after a few weeks. Heat and UV light accelerate the decreasing process. The aim of this study is to understand the physical processes of the stain creation and to find a way to make stains disappear, avoiding any damage for the painting.

An empirical formula for L line X-ray production cross-section of elements from Ag to U for protons below 3.5 MeV

When computing element concentration from proton induced X-ray emission analysis, an important parameter is the X-ray production cross-section. There have been numerous experimental and theoretical works in this field. Nonetheless, although there is a simple analytical formula to compute K X-ray cross-sections, there is no such ones for the L lines. We present here analytical formulas for the cross-section of the three main X-ray lines Lα, Lβ and Lγ based on experimental data. So far, nearly 3000 values of cross-sections for elements from Ag to U and proton energy ranging from 0.5 to 3.5 MeV have been collected from various references. This experimental data set has been fitted for each X-ray line with an exponential function depending on the proton energy and on the element atomic number. These fitted values have then been compared to the experimental data and with theoretical values obtained by the ECPSSR theory and Coster–Kronig fluorescence yields.

The exocellular DD-carboxypeptidase of Streptomyces albus G: A metallo (Zn2+) enzyme

Early experiments [l] carried out with the exocellular, 18 000 i+fr DDcarboxypeptidase excreted by Streptomyces albus G (in short the G enzyme) had shown that the activity of this enzyme was substantially inhibited by buffers, such as phosphate, which were able to complex divalent cations, and was suppressed by 2 mM ethylenediaminetetraacetate (EDTA). Since the presence of Mg2+ (or Ca’+) seemed to be required for optimal enzyme activity and stability, the G enzyme was routinely purified and assayed in the presence of 2-5 mM MgClz [2]. Contrary to various other DD-carboxypeptidases known to be serine-enzymes [3-61, the G DD-carboxypeptidase is, most likely, a metallo (Zn’+) enzyme.