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  • Author or Editor: D. Alber x
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Abstract  

Due to the essential functions of selenium-containing enzymes and the relationships between changes in the selenium status and diseases, the determination of the element and its compounds is of great interest. Radiotracer studies with 75Se have been valuable tools in selenium research. NAA and ICP-MS allow both total element and stable isotope measurements. ICP-MS in conjunction with chromatographic separation techniques and gel electrophoretic procedures coupled with scanning methods such as XRF, PIXE and laser ablation ICP-MS have been used in the determination of the selenium compounds. In this survey the application of these methods in selenium research is discussed with the help of examples on the regulation of the selenium metabolism and the detection and investigation of novel selenium-containing proteins.

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Abstract  

The effects of long-term selenium supplementation on the selenium body status were investigated in humans and rats. Selenium was determined in human muscle biopsies and monitor materials and in rat tissues by neutron activation analysis. The results showed that the body selenium load is raised by additional supply of selenomethionine or selenomethionine-containing yeast but not proportionally to the intake. The surplus selenium can serve as an endogenous source to maintain the selenoprotein levels during insufficient supply. Highly significant correlations between the muscle selenium concentrations and those in blood, blood fractions, hair and nails indicate that the selenium status can be assessed by analysis of these monitor materials.

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Abstract  

This work is about k 0-INAA using unstable neutron flux for sample irradiation. Due to slow transport, each irradiation in the channel DBVK consists of three phases: stable irradiation at the final position, and two additional irradiations during travelling by exposure to an increasing neutron flux in the delivery course and to a decreasing neutron flux in the fetch course. In this work, the neutron flux distribution along this channel was calibrated and the neutron flux variation with irradiation time was calculated, making it possible to evaluate activity growth during a complete irradiation period. The feasibility of the k 0-method was checked by analyses of four SRM-materials and three multi-element standards at three DBVK-positions. An accuracy of better than ±10% was found for nearly all determined elements in each determination.

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Abstract  

The determination of cobalt in nickel with neutron activation analysis (NAA) is hindered by an interfering nuclear reaction induced by fast neutrons. To overcome this obstacle cold neutron beam irradiation has been carried out. As a result, a cobalt concentration of 0.25±0.02 µg/g in nickel foil has been determined. This nickel foil is intended to become a reference material for neutron dosimetry.

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Abstract  

There was a confusion around the Q 0- and k 0-values for the reaction 130Ba(n,γ)131Ba. The problem was clarified in this work by re-determination of the k 0-values and critical evaluation of the Q 0-values. The new 131Ba k 0-values were found to be about 16% lower than the recommended ones compiled in 1989 and about 10% lower than those recommended in 2003. The Q 0-value was verified to be 24.3. These new values were successfully applied in k 0-INAA of Ba in various references samples. Possible error sources in Ba determination were investigated which might compensate the negative bias in Ba results from using the inaccurate k 0-values, consequently masking the problem of these old k 0-factors so far. In this context, a few cases were studied and presented.

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Abstract  

A new application of neutron transmutation doping is described. The method is useful to prepare graded zinc contents in highly pure copper materials. The research reactor BER II at the Hahn-Meitner-Institute, Berlin served as a neutron source. The zinc content produced in the samples was analyzed by determining the 65Zn-activity via gamma-spectrometry. Simultaneously irradiated flux monitors were used to determine the neutron flux density. Since cylindrical sample geometries are favorable for a reference material application in optical emission (OE) spectroscopy, the spatial distribution of the induced activity in a cylinder with a diameter of 8 mm and a length of 35 mm was investigated.

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Abstract  

Investigations have been carried out on rats to obtain information about the selenium-containing proteins present in the microsomal fraction and especially in the endoplasmatic reticulum (ER) of the kidney. For the determination of the selenium levels instrumental neutron activation analysis via 75Se was used. After labeling of rats in vivo with 75Se-selenite and separation of the proteins in the renal homogenate and cell compartments by electrophoretic methods, the 75Se-containing proteins were detected by autoradiography. In this way, six selenium-containing proteins with molecular masses of 15, 16, 20, 23-25, 40-42 and 58-60 were found in the endoplasmatic reticulum. All of those were characterized as selenocysteine-containing selenoproteins.

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Summary  

In activation analysis of traces in small samples, the non-equivalence of the activating radiation doses of sample and calibration material gives rise to sometimes tolerable systematic errors. Conversely, analysis of major components usually demands high trueness and precision. To meet this, beam geometry activation analysis (BEAMGAA) procedures have been developed for instrumental photon (IPAA) and neutron activation analysis (INAA) in which the activating neutron/photon beam exhibits broad, flat-topped characteristics. This results in a very low lateral activating flux gradient compared to known radiation facilities, however, at significantly lower flux density. The axial flux gradient can be accounted for by a monitor-sample-monitor assembly. As a first approach, major components were determined in high purity substances as well as selenium in a cattle fodder additive.

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