1,721,066 research outputs found
Gamma measurements with the 4pi BaF2 detector for the FRANZ facility
No full textThe current performance of a 4π barium fluoride gamma detector consisting of 41 modules is evaluated. It will be used to measure neutron capture events in different samples that are exposed to a neutron beam that is expected to contain up to 10^7 neutrons/(cm^2 sec). The capture cross-sections acquired in this experiment will be relevant to a multitude of different areas, for example to s-process studies, or accelerator-driven systems. The detector array was re-mounted after having been moved from Karlsruhe to Frankfurt and in the course of this process, the detector modules have been checked for their current detection properties. Every module consists of a BaF2 crystal, a photomultiplier tube connected to the crystal by sillicon oil and a voltage divider to drive the PMT, so each of them is already an individual gamma detector. Using Cobalt-60 and Caesium-137 test sources the energy resolution and - more importantly - the time resolution of every module has been determined; the results are presented in this work and compared to previous data taken at the time the detector was built initially in the mid-1980s.Für astrophysikalische Experiment soll ein aus 41 Modulen zusammengesetzter 4pi-Barium-Fluorid Gamma-Detektor Verwendung finden, dessen messtechnische Eigenschaften im Rahmen dieser Arbeit ermittelt wurden. Für verschiedene Isotope, die einem Strahl mit bis zu 10^7 Neutronen/(cm^2 sec) ausgesetzt werden, sollen Neutroneneinfangsquerschnitte gemessen werden. Die so ermittelten Querschnitte sind für zahlreiche Forschungsschwerpunkte interessant, darunter Verbesserungen der Modelle für den s-Prozess oder sog. Accelerator-driven Systems, bei denen durch einen Beschleuniger ein unterkritischer Reaktor auf kritischem Niveau gehalten wird. Das Detektor-Array wurde neu zusammengesetzt, nachdem es in Einzelteilen von Karlsruhe nach Frankfurt gebracht wurde. Während dieses Umzuges wurden die einzelnen Module, die jeweils aus einem BaF2-Kristall, einem Photomultiplier und einem die PMT versorgenden Spannungsteiler bestehen, auf ihre momentanen Eigenschaften überprüft. Um die Energie- und, wichtiger noch, die Zeitauflösung zu ermitteln, wurden Cobalt-60- und Caesium-137-Quellen benutzt; in dieser Arbeit werden die Ergebnisse vorgestellt und mit Daten verglichen, die bereits in den 1980er Jahren für diesen Detektor in Karlsruhe ermittelt wurden
Contributions of the n_TOF Collaboration to the 11th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, Pruhonice near Prague, September 2-6, 2002
No full textThe present note consists of two contributions presented by the n_TOF Collaboration, coordinated by CERN, Geneva, at the 11th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, Pruhonice (Prague), September 2-6, 2002. The two papers give an overview of techniques of measurement of neutron capture cross sections and some preliminary results of interest to ADS applications
Neutron Capture on the s-Process Branching Point Tm-171 via Time-of-Flight and Activation
Full text linkThe neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable Tm-171 (t1/2 = 1.92 yr) is part of the branching around mass A ??? 170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of Tm-171 at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A???170 branching, namely, the Yb-171 abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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