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Abstract  

An instrumental method for activation analysis based on multiparameter coincidence spectrometry is described. Practical considerations of our X- and - coincidence systems are presented. The main applications of geochemical interest are the non-destructive determinations of tin in granitic rocks and iridium in ultra-basic rocks. Some other applications to the activation analysis are proposed.

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Abstract  

One of the missions of our Institute is the promotion of basic nuclear teaching for students as well as professional teaching for workers in nuclear industry and research. For nuclear chemistry education, we present here a one day teaching course on radioactive decay and nuclear reactions, and a two or three days course based on reactor irradiation of uranium oxide, instrumental and radiochemical analysis of fission products. In the first experiment, the neutron capture is presented as an example of nuclear reaction; the neutron activation of a silver coin with a Am-Be neutron source, followed by γ-ray spectrometry, is used to identify three radionuclides of silver and to calculate their half-lives. In the second experiment, our teaching reactor is used as a neutron source with a flux about 1010 n·cm−2·s−1 at a low thermal power (10 kW). This low flux allows us to irradiate a small uranium sample which is usable for spectrometry after a short cooling time of about two hours. The first day is reserved for instrumental analysis of the fission products and a second day for the radiochemical separation of a fission radionuclides. With these experimental results, the students have to calculate the number of fissions in the irradiated sample. On optional third day for postgraduate students is devoted to the presentation of NAA and some applications as uranium determination by the fission product spectrometry.

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Abstract  

One of the basic dependent variables in the sociology of science is the rate at which scientific knowledge advances. Sociologists of science have in the past assumed that the rate of scientific advance was a function of the number of talented people entering science. This assumption was challenged by Derek Price who argued that as the number of scientists increased the number of high quality scientists would increase at a slower rate. This paper reports the results of an empirical study of changes in the size of academic physics in the U. S. between 1963 and 1975. In each year we count the number of new Assistant Professors appointed in Ph. D.-granting departments. During the early 1960s there was a sharp increase in the size of entering cohorts followed by a sharp decline. A citation analysis indicates that the proportion of each cohort publishing work which was cited at least once in the first three years after appointment was relatively constant. This leads to the conclusion that the number of scientists capable of contributing to the advance of scientific knowledge through their published research is a linear function of the total number of people entering science.

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Abstract  

The described procedure is purely instrumental. The aim is to determine efficiently the elemental composition of geological materials by neutron activation, using short-lived isotopes. Our procedure requires the use of a gamma-spectrometric system fitted with a real time correction module for the counting losses and the quasi absolute k0-method. Consequently, the two constraints inherent in the analysis of short-lived isotopes, i.e. decreasing dead time counting and relative standardization were overcome.

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Abstract  

Radio high pressure liquid chromatography (radio-HPLC) is the method of choice for quality control of radiopharmaceuticals labelled with short lived isotopes. Our preparations of “no carrier added”11C-labelled palmitic acid and L-methionine are both designed to end with a HPLC separation on either silica gel or C-18 reversed phase material. Since the crude reaction mixtures contain milligram amounts of inactive substrate materials, both separations must be carried out at preparative scale. Nevertheless they are performed in less than 10 min. The most critical factor for the separation of11C-palmitic acid from the main by-product pentadecane is the solvent composition: while the11C-L-methionine separation is especially sensitive to pH variations.

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Abstract  

A procedure is described for determining the noble metals in geological samples of varied composition (Si enriched or Cr enriched). This rapid separation procedure allows very low detection limits for all PGE (except Rh) and Ag. It uses the coprecipitation of Pd, Pt, Au, Ag and Ru with Se and Te, and the fixation of Os on an ion-exchange resin. Ir is systematically determined by epithermal NAA using multiparameter coincidence spectrometry.

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Differential scanning calorimetry (DSC) measurements have been carried out on a series of ABA poly(styrene-b-isoprene) triblock copolymers with 30% polyisoprene content and various molecular weights. The DSC data show an inward shift for the glass transition temperatures (T g) of the blocks compared to the corresponding homopolymers. As a function of the molecular weight, one to three transitions were found. The additional thirdT g gives some further evidence of the existence of an interphase between the microdomains.

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Abstract  

Our instrumental analytical method for an ultra-sensitive determination of Ir and Se in sediments and volcanic emission products is based on epithermal neutron activation analysis (ENAA) coupled with multiparameter coincidence spectrometry. An adequate setting of the energy paths and of the multiparameter coincidence spectrometry. An adequate setting of the energy paths and of the multiparameter analyzer allows a simultaneous counting of75Se and192Ir coincidences. This tool has been used to analyse different sediments sampled at the Cretaceous-Tertiary boundary (KTB) and volcanic samples in order to discuss the extra-terrestrial or volcanic origin of the Ir anomaly.

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Abstract  

The method described in a previous work to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with ammonium pyrrolidindithiocarbamate (APDC) at pH 1.5–2, has been applied to urine samples from 15 females patients suffering from cervical uterine cancer. With this type of sample the method reaches a maximum sensitivity (few ppb) with a good statistical variation (±12%). Since the highest concentration of selenium in human tissues is found in the kidney, and the elimination of this element is mainly by the urine, the method seems to be a powerful tool in the research about the human metabolism of selenium. This paper shows a possible relation of selenium concentration in human urine and the evolution time of cervical uterine cancer, in spite of limits imposed by the statistical error plus the inhomogeneity of the sample.

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European Journal of Microbiology and Immunology
Authors: Andreas Hahn, Rebecca Hinz, Thomas Meyer, Ulrike Loderstädt, Ottmar Herchenröder, Christian G. Meyer, Norbert Georg Schwarz, and Hagen Frickmann

Introduction: German sex workers have illegally established a prevention strategy, which consists of testing potential sexual partners with human immunodeficiency virus (HIV)-specific rapid diagnostic tests (RDTs) prior to engaging in unprotected sexual intercourse eventually performed in case of a negative test result. Based on a recently established modeling approach, the effectiveness of this strategy regarding the risk of HIV exposure was compared with protection provided by condom use.

Methods: Based on a literature search, the following assumptions were used for the calculations: an averaged 80% exposure risk reduction with a condom used during sexual intercourse, usage of a well-characterized 4th-generation HIV RDT, and a 10 day post-infection period without any measurable viral load in peripheral blood followed by a seroconversion period of about 3 weeks with 12.3% test sensitivity (antigen-specific) and only afterwards 97.3% (antibody-specific) test sensitivity.

Results: In most constellations, the HIV exposure risk in case of RDT-based prevention was lower than with condom use.

Conclusions: The RDT-based HIV exposure prevention as established by sex workers is effective in most situations. A notable weakness of the strategy is the RDTs' poor sensitivity in spite of a high transmission risk during the seroconversion stage.

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