Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session B3: Invited Session: New Developments in Understanding the R-Process |
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Sponsoring Units: DNP DAP Chair: Rebecca Surman, University of Notre Dame Room: Holiday 2 |
Saturday, April 11, 2015 10:45AM - 11:21AM |
B3.00001: Nuclear data sensitivities and the rapid neutron capture process Invited Speaker: Matthew Mumpower Simulations of the rapid neutron capture or $r$ process of nucleosynthesis require the input of thousands of pieces of nuclear data for which no experimental information is available. These uncertain nuclear quantities are coupled, for instance, nuclear masses effect $r$-process abundances by entering into calculations of Q-values, neutron capture rates, photo-dissociation rates, $\beta$-decay rates and the probability to emit neutrons. We report on our recent studies of nuclear data sensitivities in the $r$ process. These studies take into account the propagation of uncertainties to properly identify individual nuclei that influence $r$-process abundances over a range of nuclear models and astrophysical conditions. We additionally explore the impact of uncertainties in nuclear data on the $r$ process by performing global Monte Carlo simulations. We conclude that the reduction of nuclear data uncertainties either by new measurements or by improved nuclear models will allow for more robust $r$-process predictions. [Preview Abstract] |
Saturday, April 11, 2015 11:21AM - 11:57AM |
B3.00002: Inferring neutron capture rates of short-lived isotopes Invited Speaker: Sean Liddick Neutron capture reactions on short-lived nuclei play an important role in astrophysical processes such as the rapid neutron capture process. However, these cross sections are difficult to measure in the laboratory. The so-called beta-Oslo technique has been developed for constraining the neutron capture cross sections of short-lived nuclei by combining beta-delayed gamma-ray spectroscopy and the Oslo method to extract nuclear level densities and gamma-ray strength functions. The two quantities are used within the framework of a Hauser-Feshbach model to constrain the neutron capture cross section. The technique will be described and the inferred neutron capture cross sections for a preliminary set of nuclei presented. The experimental reach of the technique at current facilities and eventually at the upcoming Facility for Radioactive Ion Beams (FRIB) as well as the overlap with astrophysical processes will be discussed. [Preview Abstract] |
Saturday, April 11, 2015 11:57AM - 12:33PM |
B3.00003: New developments in understanding the r-process from observations of metal-poor stars Invited Speaker: Anna Frebel In their atmospheres, old metal-poor Galactic stars retain detailed information about the chemical composition of the interstellar medium at the time of their birth. Extracting such stellar abundances enables us to reconstruct the beginning of the chemical evolution shortly after the Big Bang. About 5\% of metal-poor stars with $\mbox{[Fe/H]}<-2.5$ display in their spectrum a strong enhancement of neutron-capture elements associated with the rapid (r-) nucleosynthesis process that is responsible for the production of the heaviest elements in the Universe. This fortuity provides a unique opportunity of bringing together astrophysics and nuclear physics because these objects act as ``cosmic lab'' for both fields of study. The so-called r-process stars are thought to have formed from material enriched in heavy neutron-capture elements that were created during an r-process event in a previous generation supernova. It appears that the few stars known with this rare chemical signature all follow the scaled solar r-process pattern (for the heaviest elements with 56 $\le$ Z $\le$ 90 that is). This suggests that the r-process is universal -- a surprising empirical finding and a solid result that can not be obtained from any laboratory on earth. While much research has been devoted to establishing this pattern, little attention has been given to the overall level of enhancement. New results will be presented on the full extent of r-process element enrichment as observed in metal-poor stars. The challenge lies in determining how the r-process material in the earliest gas clouds was mixed and diluted. Assuming individual r-process events to have contributed the observed r-process elements. We provide empirical estimates on the amount of r-process material produced. This should become a crucial constraint for theoretical nuclear physics models of heavy element nucleosynthesis. [Preview Abstract] |
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