1,721,047 research outputs found
Characterization of first prototypes of thin targets for the NUMEN Experiment
Full text linkThe NUMEN Experiment, at INFN-LNS, aims to get information on the nuclear matrix elements of the neutrinoless double beta decay, by measuring double charge exchange reactions cross-sections. To get a good energy resolution, target thickness must be minimized. To allow heat dissipation (intense beams will be used), around 400nm of target isotope will be deposited on a 2 μm thick highly oriented pyrolytic graphite substrate, that has high in-plane thermal conductivity. First NUMEN target prototypes of tin and tellurium have been produced. Thickness and uniformity analysis performed by alpha-particle transmission and Rutherford backscattering spectroscopy will be reported, together with the evaluation of the energy resolution with a Monte Carlo code
Thickness and uniformity characterization of thin targets for intense ion beam experiments
Full text linkThe NUMEN Experiment aims to get information on the Nuclear Matrix Elements of the Neutrinoless Double Beta Decay, by measuring heavyion induced Double Charge Exchange (DCE) reactions cross sections. A good energy resolution is needed to clearly distinguish energy states of DCE products. To measure the energy of reaction products with the required resolution, the target must be thin and uniform to minimise dispersion and straggling effects on the ejectile energy. Few hundreds of nanometers of the target isotope are deposited on a Highly Oriented Pyrolytic Graphite substrate a few micrometers thick. The results of the characterisation of the first target prototypes of tin and tellurium are presented. The Scanning Electron Microscopy was used to qualitatively analyse the samples surface. A setup to study Alpha Particle Transmission has been assembled to measure thickness and uniformity of the targets; the thickness results have been verified by the Rutherford Backscattering measurements. To evaluate the effects of the thickness on the resolution of the DCE products energy, a Monte Carlo code has been implemented, using the measured thickness and uniformity as input data for the simulation
Tests of a cooling system for thin targets submitted to intense ion beams for the numen experiment
Full text linkThe NUMEN experiment, hosted at LNS (Catania, Italy), aims to determine the Nuclear Matrix Elements (NMEs) involved in 0β β decay via heavy-ion induced Double Charge Exchange (DCE) reactions. High intensity beams of about 50 μA and of energies ranging from 15 to 60 MeV/u are necessary, due to the low DCE cross sections and the use of very thin targets (several hundreds of nm) needed to reach the required energy resolution. These intense beams produce a considerable amount of heat inside the target, which can be dissipated by depositing the targets on a highly thermally conductive substrate, HOPG (Highly Oriented Pyrolytic Graphite), and coupling it with a suitable designed target-cooler system. The heat transfer from the beam spot to the cold region has been studied by solving numerically the heat equation to determine the evolution in space and time of the temperature inside the target. According to calculations, the temperatures of most of the target isotopes remain under the melting points. Experimental tests with a laser were initiated to validate the whole cooling system and the calculations
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
Target Manipulation in Nuclear Physics Experiment with Ion Beams
Full text linkThe NUMEN project at Laboratori Nazionali del Sud of INFN studies the nuclear matrix elements of Double Charge Exchange reactions between some particular nuclei. This information will be helpful in studying the Neutrinoless Double Beta decay. Because of the very low cross-sections of such reactions, high statistics must be acquired using very intense ion beams coupled with thin targets in order to get a good resolution in energy measurements. Since the target is irradiated with low energy and intense ion beams the crucial problems are the large amount of released heat and the activation of the material. To cope with the first problem isotopes are evaporated on a graphite substrate with high thermal conductivity that will be cooled down using a cryocooler. The second issue demands for an automatic system for the target handling during the data taking of the experiment. Positioning of the target-holder with appropriate precision and contact force is a special requirement, while all materials have to be selected to suit both the large temperature range and the foreseen radiation level. This work focuses on the automatic system for target manipulation, describing its design characteristics to cope with such particular working condition and to be integrated in the experiment
Evaluation of target non-uniformity and dispersion effects on energy measurement resolution in NUMEN experiment
Full text linkIn the NUMEN Experiment, Double Charge Exchange (DCE) reactions will be studied to get very precise measurements of their cross sections and final state levels. The interest for these reactions lies in the possibility for some nuclides to have DCE with initial and final states identical to those of the Neutrinoless Double β-Decay. To reach a good precision in the energy measurements, high statistics is needed and severe constraints about the target thickness must be satisfied. A 50 μA intense ion beam will provide the desired statistics, while posing the problem of dissipating the massive heat generated in the target. It is therefore necessary to design a suitable cooling system, which must affect the particles' energy as little as possible. Said energy is already influenced by the current setup. The Superconducting Cyclotron (SC) and the MAGNEX Spectrometer introduce an error on the particles' energy by 1/1000th (FWHM value) of its average energy. In the target, the main sources of error are straggling of projectiles and reaction products, and the dispersion effect. Both closely depend on the target thickness, which must be of the order of few hundred nanometres. In addition, the two effects are worsened if the target thickness is not uniform. The solution to these problems has been found by backing the target isotope with relatively thin substrate of Highly Oriented Pyrolytic Graphite (HOPG). Its thermodynamic properties fit the cooling requirements and can be as thin as 450 μg cm-2. The further straggling suffered by the ejectiles is tolerable, falling within the resolution requirements. Samples are deposited by using Electron Beam Evaporation: results obtained for Sn and Te are checked by Scanning Electron Microscopy (SEM). A quantitative evaluation of the samples' thickness has been performed by Alpha-Particle Transmission (APT) and Rutherford Backscattering Spectrometry (RBS) measurements. A Monte Carlo code has been implemented to estimate the ejectiles energy distribution using the experimental measurements as input. Results from characterization and simulations help in optimizing the target thickness and the energy resolution of reaction products
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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