New <sup>88</sup>Sr(n,<font face="symbol">g</font>)Astrophysical Reaction Rate from Resonance Analysis of New High-Resolution Neutron Capture and Transmission Data Page: 1 of 8
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New 88Sr(n,7) Astrophysical Reaction
Rate from Resonance Analysis of New
High-Resolution Neutron Capture and
Transmission Data
P. E. Koehler
Physics Division, Oak Ridge National Laboratory
Abstract. Because of its small cross section, the 85Sr(n,y) reaction is an important
bottleneck during s-process nucleosynthesis. Hence, an accurate determination of this
rate is needed to better constrain the neutron exposure in s-process models and to
more fully exploit the recently discovered isotopic anomalies in certain meteorites. We
have completed the resonance analysis of our new and improved measurements of the
neutron capture and total cross sections for 85Sr made at the Oak Ridge Electron
Linear Accelerator (ORELA). We describe our experimental procedures and resonance
analysis, compare our results to previous data, and discuss their astrophysical impact.
I INTRODUCTION
The 8Sr(n, y) cross section is important to nuclear astrophysics for at least three
reasons. (i) Because this cross section is very small, "Sr acts as a bottleneck in
s-process nucleosynthesis [1]. The A t 100 region is complicated, with several
different nucleosynthesis processes contributing to the abundances of nuclides in
this region. Because of its bottleneck character, it is crucial to know accurately
the cross section for the 8Sr(n, y) reaction so that the relative contributions of
various processes to the solar system abundances can be disentangled. (ii) It has
been shown that a measurement of the Rb/Sr ratio in stars can be used to extract
the neutron density during the s process. Current results [2] indicate that the neu-
tron density derived from these data is consistent only with the s process occurring
during the interpulse phase in low mass asymptotic giant branch (AGB) stars. Be-
cause the cross sections were not measured to low enough energies to determine
the low-temperature reaction rates needed in the models, this conclusion is based
mainly on extrapolations of previous neutron capture measurements. Strontium is
the normalization point for these data and strontium is mostly 'Sr. Therefore,
new measurements of the MSr(n, 7) cross section are needed at lower neutron en-
ergies to provide a more robust test of stellar models. (iii) Non-solar ratios for
isotopes of strontium and other elements have been observed in SiC grains in cer-
Tire submitted manuscript ag been
authored by a contractor ot the U. S.
Government under contract No. DE-
A005-seoR24e. Accordingly, the U. S.
.ovemment retains a noriexluslve.
royalty-tree license to publish or reproduce
the published torm of this contribution, or
allow others to do so, for U.S. Government
purposes."
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Koehler, P. E. New <sup>88</sup>Sr(n,<font face="symbol">g</font>)Astrophysical Reaction Rate from Resonance Analysis of New High-Resolution Neutron Capture and Transmission Data, article, August 30, 1999; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc628444/m1/1/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.