489 research outputs found
Studies of radioactive nuclei and their role in the cosmos
Producing and accelerating radioactive nuclei in the laboratory provides a unique tool for the study of nuclear reactions involving these isotopes in the energy regime of interest for astrophysics. We briefly review some recent developments with accelerated radioactive ion beams and their impact for astrophysics. © Copyright owned by the author(s)
What do (and don\u27t) we understand about explosive nucleosynthesis?
Isotopic abundances reflect both nuclear structure and environmental history. Observations are providing new evidence that is helping us to understand astrophysical phenomena, the chemical history of the Galaxy, and the origins of the diverse isotopic abundances found on earth. What we infer from observations, however, depends upon a robust understanding of the underlying nuclear physics. The difficulties involved in producing and studying short-lived isotopes are particularly problematic for understanding stellar explosions. While new facilities and experimental techniques have recently spurred significant progress in our understanding of the light, proton-rich nuclei that are important for understanding novae, studies of heavier exotic nuclei that are crucial for understanding more energetic explosions and the origins of the heavy elements are still quite challenging. We briefly survey recent progress in experimental nuclear physics that is important for understanding explosive nucleosynthesis and outline some of the major outstanding questions and the prospects for future advances
Neutron capture on \u3csup\u3e130\u3c/sup\u3eSn during r-process freeze-out
We examine the role of neutron capture on 130Sn during r-process freeze-out in the neutrino-driven wind environment of the core-collapse supernova. We find that the global r-process abundance pattern is sensitive to the magnitude of the neutron capture cross section of 130Sn. The changes to the abundance pattern include not only a relative decrease in the abundance of 130Sn and an increase in the abundance of 131Sn, but also a shift in the distribution of material in the rare earth and third peak regions. © 2009 IOP Publishing Ltd
Unbound states of 32Cl and the 31S(p,\gamma)32Cl reaction rate
The 31S(p,\gamma)32Cl reaction is expected to provide the dominant break-out
path from the SiP cycle in novae and is important for understanding enrichments
of sulfur observed in some nova ejecta. We studied the 32S(3He,t)32Cl
charge-exchange reaction to determine properties of proton-unbound levels in
32Cl that have previously contributed significant uncertainties to the
31S(p,\gamma)32Cl reaction rate. Measured triton magnetic rigidities were used
to determine excitation energies in 32Cl. Proton-branching ratios were obtained
by detecting decay protons from unbound 32Cl states in coincidence with
tritons. An improved 31S(p,\gamma)32Cl reaction rate was calculated including
robust statistical and systematic uncertainties
The Single-Particle Structure of Neutron-Rich Nuclei of Astrophysical Interest at the Ornl Hribf
The rapid nuetron-capture process (r process) produces roughly half of the
elements heavier than iron. The path and abundances produced are uncertain,
however, because of the lack of nuclear strucure information on important
neutron-rich nuclei. We are studying nuclei on or near the r-process path via
single-nucleon transfer reactions on neutron-rich radioactive beams at ORNL's
Holifield Radioactive Ion Beam Facility (HRIBF). Owing to the difficulties in
studying these reactions in inverse kinematics, a variety of experimental
approaches are being developed. We present the experimental methods and initial
results.Comment: Proceedings of the Third International Conference on Fission and
Properties of Neutron-Rich Nucle
Building a Model of Collaboration Between Historically Black and Historically White Universities
Despite increases over the last two decades in the number of degrees awarded to students from underrepresented groups in science, technology, engineering, and mathematics (STEM) disciplines, enhancing diversity in these disciplines remains a challenge. This article describes a strategic approach to this challenge—the development of a collaborative partnership between two universities: the historically Black Elizabeth City State University and the historically White University of New Hampshire. The partnership, a type of learning organization built on three mutually agreed upon principles, strives to enhance opportunities for underrepresented students to pursue careers in the STEM disciplines. This article further describes six promising practices that framed the partnership, which resulted in the submission of nine proposals to federal agencies and the funding of four grants that led to the implementation, research, learning, and evaluation that followed
Direct reaction measurements with a 132Sn radioactive ion beam
The (d,p) neutron transfer and (d,d) elastic scattering reactions were
measured in inverse kinematics using a radioactive ion beam of 132Sn at 630
MeV. The elastic scattering data were taken in a region where Rutherford
scattering dominated the reaction, and nuclear effects account for less than 8%
of the cross section. The magnitude of the nuclear effects was found to be
independent of the optical potential used, allowing the transfer data to be
normalized in a reliable manner. The neutron-transfer reaction populated a
previously unmeasured state at 1363 keV, which is most likely the
single-particle 3p1/2 state expected above the N=82 shell closure. The data
were analyzed using finite range adiabatic wave calculations and the results
compared with the previous analysis using the distorted wave Born
approximation. Angular distributions for the ground and first excited states
are consistent with the previous tentative spin and parity assignments.
Spectroscopic factors extracted from the differential cross sections are
similar to those found for the one neutron states beyond the benchmark
doubly-magic nucleus 208Pb.Comment: 22 pages, 7 figure
New Features in the Computational Infrastructure for Nuclear Astrophysics
A Computational Infrastructure for Nuclear Astrophysics has been developed to streamline the inclusion of the latest nuclear physics data in astrophysics simulations. The infrastructure consists of a platform-independent suite of computer codes that are freely available online at http://nucastrodata.org. The newest features of, and future plans for, this software suite are given. © Copyright owned by the author(s)
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