Entity

Time filter

Source Type

Durham, NC, United States

Mitchell G.E.,North Carolina State University | Mitchell G.E.,Triangle Universities Nuclear Laboratory | Richter A.,TU Darmstadt | Weidenmuller H.A.,Max Planck Institute for Nuclear Physics
Reviews of Modern Physics | Year: 2010

The application of random-matrix theory (RMT) to compound-nucleus (CN) reactions is reviewed. An introduction into the basic concepts of nuclear scattering theory is followed by a survey of phenomenological approaches to CN scattering. The implementation of a random-matrix approach into scattering theory leads to a statistical theory of CN reactions. Since RMT applies generically to chaotic quantum systems, that theory is, at the same time, a generic theory of quantum chaotic scattering. It uses a minimum of input parameters (average S matrix and mean level spacing of the CN). Predictions of the theory are derived with the help of field-theoretical methods adapted from condensed-matter physics and compared with those of phenomenological approaches. Thorough tests of the theory are reviewed, as are applications in nuclear physics, with special attention given to violation of symmetries (isospin and parity) and time-reversal invariance. © 2010 The American Physical Society.


Gould C.R.,North Carolina State University | Gould C.R.,Triangle Universities Nuclear Laboratory | Sharapov E.I.,Joint Institute for Nuclear Research
Physical Review C - Nuclear Physics | Year: 2012

Background: Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures T O which in turn impacts bounds on time variation of the fine structure constant α. Purpose: We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio Bg in 175Lu neutron capture at 5 and 25 keV. Method: We recalculate predictions for T O as a function of Bg using realistic models of the Oklo neutron flux. Results: We find T O=100±30 -C using a new value of Bg, in contrast to 350


Oginni B.M.,Triangle Universities Nuclear Laboratory | Iliadis C.,University of North Carolina at Chapel Hill | Champagne A.E.,University of North Carolina at Chapel Hill
Physical Review C - Nuclear Physics | Year: 2011

The reactions that destroy Al26 in massive stars have significance in a number of astrophysical contexts. We evaluate the reaction rates of Al26(n,p)26Mg and Al26(n,α)23Na using cross sections obtained from the codes empire and talys. These have been compared to the published rates obtained from the non-smoker code and to some experimental data. We show that the results obtained from empire and talys are comparable to those from non-smoker. We also show how the theoretical results vary with respect to changes in the input parameters. Finally, we present recommended rates for these reactions using the available experimental data and our new theoretical results. © 2011 American Physical Society.


Jose J.,Polytechnic University of Catalonia | Jose J.,Institute Destudis Espacials Of Catalonia Ieec | Moreno F.,Polytechnic University of Catalonia | Parikh A.,TU Munich | And 2 more authors.
Astrophysical Journal, Supplement Series | Year: 2010

Type I X-ray bursts (XRBs) are thermonuclear stellar explosions driven by charged-particle reactions. In the regime for combined H/He-ignition, the main nuclear flow is dominated by the rp-process (rapid proton-captures and β+-decays), the 3α-reaction, and the αp-process (a suite of (α, p) and (p, γ) reactions). The main flow is expected to proceed away from the valley of stability, eventually reaching the proton drip line beyond A = 38. Detailed analysis of the relevant reactions along the main path has only been scarcely addressed, mainly in the context of parameterized one-zone models. In this paper, we present a detailed study of the nucleosynthesis and nuclear processes powering type I XRBs. The reported 11 bursts have been computed by means of a spherically symmetric (one-dimensional), Lagrangian, hydrodynamic code, linked to a nuclear reaction network that contains 325 isotopes (from 1H to 107Te), and 1392 nuclear processes. These evolutionary sequences, followed from the onset of accretion up to the explosion and expansion stages, have been performed for two different metallicities to explore the dependence between the extension of the main nuclear flow and the initial metal content. We carefully analyze the dominant reactions and the products of nucleosynthesis, together with the physical parameters that determine the light curve (including recurrence times, ratios between persistent and burst luminosities, or the extent of the envelope expansion). Results are in qualitative agreement with the observed properties of some well-studied bursting sources. Leakage from the predicted SbSnTe cycle cannot be discarded in some of our models. Production of 12C (and implications for the mechanism that powers superbursts), light p-nuclei, and the amount of H left over after the bursting episodes will also be discussed. © 2010. The American Astronomical Society.


Jose J.,Polytechnic University of Catalonia | Jose J.,Institute Destudis Espacials Of Catalonia | Iliadis C.,University of North Carolina at Chapel Hill | Iliadis C.,Triangle Universities Nuclear Laboratory
Reports on Progress in Physics | Year: 2011

Half a century has passed since the foundation of nuclear astrophysics. Since then, this discipline has reached its maturity. Today, nuclear astrophysics constitutes a multidisciplinary crucible of knowledge that combines the achievements in theoretical astrophysics, observational astronomy, cosmochemistry and nuclear physics. New tools and developments have revolutionized our understanding of the origin of the elements: supercomputers have provided astrophysicists with the required computational capabilities to study the evolution of stars in a multidimensional framework; the emergence of high-energy astrophysics with space-borne observatories has opened new windows to observe the Universe, from a novel panchromatic perspective; cosmochemists have isolated tiny pieces of stardust embedded in primitive meteorites, giving clues on the processes operating in stars as well as on the way matter condenses to form solids; and nuclear physicists have measured reactions near stellar energies, through the combined efforts using stable and radioactive-ion beam facilities. This review provides comprehensive insight into the nuclear history of the Universe and related topics: starting from the Big Bang, when the ashes from the primordial explosion were transformed to hydrogen, helium and a few trace elements, to the rich variety of nucleosynthesis mechanisms and sites in the Universe. Particular attention is paid to the hydrostatic processes governing the evolution of low-mass stars, red giants and asymptotic giant-branch stars, as well as to the explosive nucleosynthesis occurring in core-collapse and thermonuclear supernovae, γ-ray bursts, classical novae, x-ray bursts, superbursts and stellar mergers. © 2011 IOP Publishing Ltd.

Discover hidden collaborations