1,721,295 research outputs found
Excitation of isospin and spin-isospin modes in the beta(+) direction
No full textThe excitation of isospin and spin-isospin modes has been a topic of much interest in the last two decades because of their importance to various astrophysical phenomena next to the intrinsic interest in their microscopic structure. (p, n) and other (p,n)-type reactions, such as (He-3,t), at intermediate energies have been used to map spin-isospin-flip strength in the beta(-) direction. For the beta(+) direction the spin-isospin-flip strength can, in principle, be mapped with the (n,p) reaction at intermediate energies. However, the resolution that can be obtained with secondary neutron beams is hardly useful to map accurately this strength. Better reactions could be (d, He-2) and (t,He-3) reactions at intermediate energies. Recently, at KVI a primary triton beam has been accelerated to energies of about 45 MeV/u. It is planned to use this beam to study isospin excitations in 'neutron-rich' nuclei. Furthermore, an unprecedented high resolution of 150 keV has been achieved with the (d,2He) reaction, which is a reaction of essentially pure spin- and isospin-flip character. This allows to map the spin-isospin strength and study its microscopic and multipole structure. Recent experimental results axe discussed.</p
On the excitation of isoscalar dipole strength in the giant resonance region by inelastic electron and hadron scattering
Full text linkThe possible excitation of isoscalar dinole strength in the region of the giant resonances is investigated. The presence of 20% of the isoscalar dipole energy-weighted sum rule (EWSR) in the region of the giant quadrupole resonance (GQR) would have an appreciable cross section as compared to the total cross section attributed to GQR excitation, and would readily account for the forward-backward asymmetries observed in α0-decay of the GQR in light nuclei
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
A REVIEW OF THE FISSION DECAY OF THE GIANT-RESONANCES IN THE ACTINIDE REGION
No full textLa décroissance par fission des résonances géantes dans la région des actinides est passée en revue. Les résultats invariablement contradictoires de diverses expériences sont discutés. Celles-ci comprennent des réactions inclusives de fission induite par électron ou positron, et des expériences où les fragments de fission sont détectés en coïncidence avec les électrons ou hadrons diffusés inélastiquement. Nous nous concentrons sur une expérience (α,α'f) récente où l'on étudie la décroissance par fission de la résonance géante monopolaire en détectant les fragments de fission en coïncidence avec les α inélastiques autour de, et à 0°.The fission decay of giant resonances in the actinide region is reviewed. Results from various experiments which are invariably conflicting are discussed. These include inclusive electron and positron induced fission, as well as experiments in which fission fragments were detected in coincidence with inelastically scattered electrons or hadrons. Attention is focussed on a recent (α,α'f) experiment in which the fission decay of the giant monopole resonance was investigated by measuring fission fragments in coincidence with inelastically scattered α-particles at and around 0°
GDR excitation by isoscalar probes: a means to determine the neutron-skin thickness
No full textInelastic scattering of a-particles can excite the isovector giant dipole resonance (GDR) via the Coulomb interaction. In spite of their isoscalar nature alpha-particles carl also excite the GDR via the nuclear interaction due to the difference in the radii of the neutron and proton density distributions. The absolute cross section to excite the GDR in inelastic alpha-scattering is therefore a measure of this radial difference, the so-called neutron-skin thickness. Furthermore, since the GDR strength distribution has a centroid energy which depends on the nuclear radius, these studies, when performed in deformed nuclei, can measure the neutron-skin thickness along both the short and the long axes independently. Results of an experiment performed at KVI at E-alpha = 120 MeV and small scattering angles, including 0 degrees, to determine the neutron-skin thickness in Pb-208, Sn-116, Sn-124, and the deformed Nd-150 are discussed and compared to earlier measurements and theoretical predictions. Future improvements in the experimental set-up are also 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
Hadronic excitation of the octupole bands in deformed nuclei: Necessity of the isoscalar dipole degree of freedom?
Full text linkCoupled channel analysis indicates that an octupole vibration coupled to the quadrupole static deformation is sufficient to explain the inelastic excitation by proton scattering of the K ~r = 0- octupole band in lS2Sm. The isoscalar dipole degree of freedom is found not to be necessary, at least for this mass region, to explain the excitation of the 1- state of the octupole band
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