210 research outputs found
Particle-particle random phase approximation applied to Beryllium isotopes
This work is dedicated to the study of even-even 8-14 Be isotopes using the
particle-particle Random Phase Approximation that accounts for two-body
correlations in the core nucleus. A better description of energies and
two-particle amplitudes is obtained in comparison with models assuming a
neutron closed-shell (or subshell) core. A Wood-Saxon potential corrected by a
phenomenological particle-vibration coupling term has been used for the
neutron-core interaction and the D1S Gogny force for the neutron-neutron
interaction. Calculated ground state properties as well as excited state ones
are discussed and compared to experimental data. In particular, results suggest
the same 2s_1/2-1p_1/2 shell inversion in 13Be as in 11Be.Comment: to appear in Phys. Rev.
Quaternary development of resilient reefs on the subsiding kimberley continental margin, Northwest Australia
The Kimberley region in remote northwest Australia has poorly known reef systems of two types; coastal fringing reefs and atoll-like shelf-edge reefs. As a major geomorphic feature (from 12ºS to 18ºS) situated along a subsiding continental margin, the shelf edge reefs are in a tropical realm with warm temperatures, relatively low salinity, clear low nutrient waters lacking sediment input, and Indo-West Pacific corals of moderate diversity. Seismic architecture of the Rowley Shoals reveals that differential pre-Holocene subsidence and relative elevation of the pre-Holocene substrate have controlled lagoon sediment infill and reef morphology, forming an evolutionary series reflecting differential accommodation in three otherwise similar reef systems.The Holocene core described for North Scott Reef confirms previous seismic interpretations, and provides a rare ocean-facing reef record. It demonstrates that the Indo-Pacific reef growth phase (RG111) developed during moderate rates of sea level rise of 10 mm/year from 11 to about 7-6.5 ka BP until sea level stabilization, filling the available 27 m of pre-Holocene accommodation. Despite the medium to high hydrodynamic energy imposed by the 4m tides, swell waves and cyclones the reef-building communities represent relatively low-wave energy settings due to their southeast facing and protection afforded by the proximity of the South Reef platform. This study demonstrates the resilience of reefs on the subsiding margin whilst linking Holocene reef morphology to the relative amount of pre-Holocene subsidence
Single-Proton Removal Reaction Study of 16B
The low-lying level structure of the unbound system B has been
investigated via single-proton removal from a 35 MeV/nucleon C beam. The
coincident detection of the beam velocity B fragment and neutron allowed
the relative energy of the in-flight decay of B to be reconstructed. The
resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is
argued that this feature corresponds to a very narrow (100 keV)
resonance, or an unresolved multiplet, with a dominant + configuration which decays by d-wave neutron
emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.
Resolving the ancestry of Austronesian-speaking populations
There are two very different interpretations of the prehistory of Island Southeast Asia (ISEA), with genetic evidence invoked in support of both. The “out-of-Taiwan” model proposes a major Late Holocene expansion of Neolithic Austronesian speakers from Taiwan. An alternative, proposing that Late Glacial/postglacial sea-level rises triggered largely autochthonous dispersals, accounts for some otherwise enigmatic genetic patterns, but fails to explain the Austronesian language dispersal. Combining mitochondrial DNA (mtDNA), Y-chromosome and genome-wide data, we performed the most comprehensive analysis of the region to date, obtaining highly consistent results across all three systems and allowing us to reconcile the models. We infer a primarily common ancestry for Taiwan/ISEA populations established before the Neolithic, but also detected clear signals of two minor Late Holocene migrations, probably representing Neolithic input from both Mainland Southeast Asia and South China, via Taiwan. This latter may therefore have mediated the Austronesian language dispersal, implying small-scale migration and language shift rather than large-scale expansion
Optical potentials for the rare-isotope beam era
We review recent progress and motivate the need for further developments in
nuclear optical potentials that are widely used in the theoretical analysis of
nucleon elastic scattering and reaction cross sections. In regions of the
nuclear chart away from stability, which represent a frontier in nuclear
science over the coming decade and which will be probed at new rare-isotope
beam facilities worldwide, there is a targeted need to quantify and reduce
theoretical reaction model uncertainties, especially with respect to nuclear
optical potentials. We first describe the primary physics motivations for an
improved description of nuclear reactions involving short-lived isotopes,
focusing on its benefits for fundamental science discoveries and applications
to medicine, energy, and security. We then outline the various methods in use
today to build optical potentials starting from phenomenological, microscopic,
and ab initio methods, highlighting in particular the strengths and weaknesses
of each approach. We then discuss publicly-available tools and resources
facilitating the propagation of recent progresses in the field to
practitioners. Finally, we provide a set of open challenges and recommendations
for the field to advance the fundamental science goals of nuclear reaction
studies in the rare-isotope beam era.Comment: This paper is the outcome of the Facility for Rare Isotope Beams
Theory Alliance (FRIB - TA) topical program "Optical Potentials in Nuclear
Physics" held in March 2022 at FRIB. Its content is non-exhaustive, was
chosen by the participants and reflects their efforts related to optical
potential
Non local microscopic potentials for calculation of scattering observables of nucleons on deformed nuclei
Comprehensive investigation of fission yields by using spallation- and (p,2p)-induced fission reactions in inverse kinematics
In the last decades, measurements of spallation, fragmentation and Coulex
induced fission reactions in inverse kinematics have provided valuable data to
accurately investigate the fission dynamics and nuclear structure at large
deformations of a large variety of stable and non-stable heavy nuclei. To go a
step further, we propose now to induce fission by the use of quasi-free (p,2p)
scattering reactions in inverse kinematics, which allows us to reconstruct the
excitation energy of the compound fissioning system by using the four-momenta
of the two outgoing protons. Therefore, this new approach might permit to
correlate the excitation energy with the charge and mass distributions of the
fission fragments and with the fission probabilities, given for the first time
direct access to the simultaneous measurement of the fission yield dependence
on temperature and fission barrier heights of exotic heavy nuclei,
respectively. The first experiment based on this methodology was realized
recently at the GSI/FAIR facility and a detailed description of the
experimental setup is given here.Comment: 4 pages, 15th International Conference on Nuclear Data for Science
and Technology (ND2022
Caribbean-wide decline in carbonate production threatens coral reef growth
This a post-print, author-produced version of an article accepted for publication in Nature Communications. Copyright © 2013 Nature Publishing Group . The definitive version is available at http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2409.htmlGlobal-scale deteriorations in coral reef health have caused major shifts in species composition. One projected consequence is a lowering of reef carbonate production rates, potentially impairing reef growth, compromising ecosystem functionality and ultimately leading to net reef erosion. Here, using measures of gross and net carbonate production and erosion from 19 Caribbean reefs, we show that contemporary carbonate production rates are now substantially below historical (mid- to late-Holocene) values. On average, current production rates are reduced by at least 50%, and 37% of surveyed sites were net erosional. Calculated accretion rates (mm year(-1)) for shallow fore-reef habitats are also close to an order of magnitude lower than Holocene averages. A live coral cover threshold of ~10% appears critical to maintaining positive production states. Below this ecological threshold carbonate budgets typically become net negative and threaten reef accretion. Collectively, these data suggest that recent ecological declines are now suppressing Caribbean reef growth potential
Quasi-free (p,2p) reactions in inverse kinematics for studying the fission yield dependence on temperature
Despite the recent experimental and theoretical progress in the investigation of the nuclear fission process, a complete description still represents a challenge in nuclear physics because it is a very complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. To improve on the existing data on nuclear fission,we produce fission reactions of heavy nuclei in inverse kinematics by using quasi-free (p,2p) scattering, which induce fission through particle-hole excitations that can range from few to ten\u27s of MeV. The measurement of the four-momenta of the two outgoing protons allows to reconstruct the excitation energy of the fissioning nucleus and therefore to study the evolution of the fission yields with temperature. The realization of this kind of experiment requires a complex experimental setup, providing full isotopic identification of both fission fragments and an accurate measurement of the momenta of the two outgoing protons. This was realized recently at the GSI/FAIR facility and here some preliminary results are presented
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