Search Results

You are looking at 1 - 10 of 12 items for

  • Author or Editor: G. Weber x
  • All content x
Clear All Modify Search

Abstract  

Although Neutron Activation Analysis is usually not very common in aerosol physics, there are fields of application which seem to be rather successful. In general it is shown which properties activable aerosols should have, how they can be produced and how aerosol samples might be drawn. By use of special aerosol separators not only the mass-concentration but also the size-distribution of the aerosol can be determinated. Based on two studies, the utility of activable aerosols is demonstrated: Calibration and test of a simple discontinously working aerosol monitor for the off-gass system of isotope hoods; dynamic o radioactive ionized aerosols in a sealed room. Finally a general survey of further applications of activable aerosols is given.

Restricted access

Abstract  

The different important stages of the development of proton induced X-ray emission (PIXE) spectrometry utilised with success since 1976 at Liège University are outlined. The methodological efforts (irradiation, target preparation, calibration, matrix effect corrections) to improve quantitative trace element analysis are emphasized. Examples of applications in geological, biomedical and environmental sciences are selected in order to illustrate the potential of the technique in these fields.

Restricted access

Abstract  

After a brief account of the general principles of the method, a description is given of some aspects of the problems which have been investigated in detail: behaviour of targets under ion-bombardment, determination of oxygen, carbon and nitrogen at the surface of metallic targets, and determination of carbon and nitrogen in tantalum layers metallized on glass.

Restricted access

Abstract  

A fast and precise method of determining fluorine in geological matrices is proposed. The 0.20 MeV photopeak of19O, induced by the19F(n, p)19O reaction, was used for this assay. Neutron flux monitoring was achieved by adding an internal standard monitor (20 mg Ce) to each sample and counting the activity due to the 0.74 MeV photopeak of139mCe, produced in the140Ce(n, 2n)139mCe reaction. This activity was considered to be proportional to the neutron flux during the sample irradiation. This method of fluorine determination was checked on two fluorine geological standards, mica and apatite, containing 1.50 and 2.90% fluorine, respectively. The sensitivity of the method, obviously depending upon the matrix composition, was 1.46 mg for the mica standard.

Restricted access

Abstract  

The use of 2.8 MeV neutrons produced by the D(d, n)3He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·106 n·cm−2·sec−1 on the sample.

Restricted access

Abstract  

The physisorption of trichloroethylene and tetrachloroethylene on ZSM-5 (Si/Al = 339) zeolite was investigated at 298 K using thermogravimetry, differential microcalorimetry and X-ray diffraction. The zeolite always undergoes a monoclinic-orthorhombic structural change during the adsorption of the first molecules. An alignment of the polar trichloroethylene molecules inside all the channels of the zeolite is proposed to account for the experimental results. A phase transition of the non-polar tetrachloroethylene is suggested to produce the stepped isotherm, the steep rise in the heat curve and the high increase in the mobility of the molecules for the loading of 4 molecules per unit cell.

Restricted access

Résumé  

Dans un programme de recherche visant à étudier les différentes méthodes de dosage de l'oxygène dans les métaux non ferreux, nous avons été amenés à examiner l'influence de l'oxygène de surface sur la détermination de l'oxygène dans la masse. Cette analyse de la surface a été réalisée en utilisant les réactions nucléaires induites par des particules chargées de faible énergie obtenues à l'aide d'un accélérateur Van de Graaff de 2 Mev.

Restricted access

Inclusion by a fluorenyl diol host with substituted pyridines

Structures, selectivity and kinetics of desorption

Journal of Thermal Analysis and Calorimetry
Authors: L. Nassimbeni, G. Ramon, and E. Weber

Abstract  

The structures of the inclusion compounds formed by the host 9,9’-(ethyne-1,2-diyl)bis(fluoren-9-01) with pyridine and picolines are similar and display tubular topology. The host discriminates poorly between these guests. The kinetics of desorption of the pyridine compound is governed by the Avrami-Erofe’ev equation A2, with an activation energy of 111(7) kJ mol−1.

Restricted access

Abstract  

More than 200 specimens from different occurrences of the Rogaland igneous complex and surrounding granulite facies metamorphic rocks (S. W. Norway) have been analysed by a direct non-destructive proton induced gamma-ray emission (PIGE) technique. The fluorine contents vary from <25 ppm to 3500 ppm. There is a good correlation between the concentration of fluorine and that of phosphorus for igneous rocks, suggesting a control of apatite on the F content. In metamorphic rocks, amphibole and biotite besides apatite are the principal cencentrators of fluorine indicating that fluorine in the system is controlled by granulite facies metamorphism conditions.

Restricted access

Abstract  

Surface treatment on non-ferrous metals are proposed in order to minimize or determine quantitatively the interference of gaseous contamination. These proposals result from a large number of determinations of superficial contamination on several materials using microanalysis by nuclear reactions. This work is included in a larger program which aims the certification of standard materials in their oxygen, nitrogen and carbon contents.

Restricted access