Neutron Capture and the Production of 60-Fe in Stellar Environments

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The observation of gamma rays associated with the decay of {sup 26}Al and {sup 60}Fe can provide important information regarding ongoing nucleosynthesis in our galaxy. The half-lives of these radioisotopes (7.2 x 10{sup 5} y and 1.5 x 10{sup 6} y, respectively) are long compared to the interval between synthesis events such as supernovae, so they build up in a steady state in the interstellar medium (centered on the galactic plane, where massive stars reside), yet short enough that gamma radiation from their decay may be detected. Additionally, these half-lifes are short compared to the period of galactic revolution, so ... continued below

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PDF-file: 280 pages; size: 3.6 Mbytes

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Kelley, K August 23, 2005.

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The observation of gamma rays associated with the decay of {sup 26}Al and {sup 60}Fe can provide important information regarding ongoing nucleosynthesis in our galaxy. The half-lives of these radioisotopes (7.2 x 10{sup 5} y and 1.5 x 10{sup 6} y, respectively) are long compared to the interval between synthesis events such as supernovae, so they build up in a steady state in the interstellar medium (centered on the galactic plane, where massive stars reside), yet short enough that gamma radiation from their decay may be detected. Additionally, these half-lifes are short compared to the period of galactic revolution, so that observable abundances remain in the proximity of their production sites. Predicted abundances of {sup 26}Al and {sup 60}Fe vary widely between several calculations in the last decade. In 2004, the first observation of the gamma ray flux from {sup 60}Fe decay was reported, with a {sup 60}Fe/{sup 26}Al flux ratio in good agreement with nucleosynthesis modeling from 1995. However, recent calculations that include well motivated updates to the stellar and nuclear physics, predict a flux ratio as much as six times higher than the observed value. It is desirable to understand the discrepancy between the latest calculation, which in principle should have been more accurate, and the observation. In the present study, the uncertainties related to two key nuclear aspects of this problem, namely the neutron capture reaction rates for {sup 59,60}Fe, are investigated. New reaction rates are modeled using local systematics as opposed to the global systematics used in previous studies. Comparisons to experimental data are made whenever possible. The sensitivity of the reaction rates to various input quantities is gauged, and estimates regarding the total uncertainty in the reaction rates are made. The resulting rates and uncertainties are used in parameterized single-zone nucleosynthesis calculations using hydrodynamic conditions typical of those found in more complex stellar models. Finally, the sensitivity of the abundance of {sup 60}Fe to the reaction rates is discussed.

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PDF-file: 280 pages; size: 3.6 Mbytes

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  • Report No.: UCRL-TH-215351
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 877893
  • Archival Resource Key: ark:/67531/metadc876733

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • August 23, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • Nov. 30, 2016, 12:41 p.m.

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Kelley, K. Neutron Capture and the Production of 60-Fe in Stellar Environments, thesis or dissertation, August 23, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc876733/: accessed November 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.