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Title: Expectations for {sup 12}C and {sup 16}O induced fusion cross sections at energies of astrophysical interest

Abstract

The extrapolations of cross sections for fusion reactions involving {sup 12}C and {sup 16}O nuclei down to energies relevant for explosive stellar burning have been reexamined. Based on a systematic study of fusion in heavier systems, it is expected that a suppression of the fusion process will also be present in these light heavy-ion systems at extreme sub-barrier energies due to the saturation properties of nuclear matter. Previous phenomenological extrapolations of the S factor for light heavy-ion fusion based on optical model calculations may therefore have overestimated the corresponding reaction rates. A new ''recipe'' is proposed to extrapolate S factors for light heavy-ion reactions to low energies taking the hindrance behavior into account. It is based on a fit to the logarithmic derivative of the experimental cross section which is much less sensitive to overall normalization discrepancies between different data sets than other approaches. This method, therefore, represents a significant improvement over other extrapolations. The impact on the astrophysical reaction rates is discussed.

Authors:
; ; ;  [1]
  1. Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
Publication Date:
OSTI Identifier:
20990980
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevC.75.015803; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CARBON 12; CROSS SECTIONS; EXPLOSIVES; EXTRAPOLATION; HEAVY ION REACTIONS; HEAVY IONS; NUCLEAR MATTER; OPTICAL MODELS; OXYGEN 16; REACTION KINETICS; STAR BURNING; VISIBLE RADIATION

Citation Formats

Jiang, C. L., Rehm, K. E., Back, B. B., and Janssens, R. V. F. Expectations for {sup 12}C and {sup 16}O induced fusion cross sections at energies of astrophysical interest. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.015803.
Jiang, C. L., Rehm, K. E., Back, B. B., & Janssens, R. V. F. Expectations for {sup 12}C and {sup 16}O induced fusion cross sections at energies of astrophysical interest. United States. doi:10.1103/PHYSREVC.75.015803.
Jiang, C. L., Rehm, K. E., Back, B. B., and Janssens, R. V. F. Mon . "Expectations for {sup 12}C and {sup 16}O induced fusion cross sections at energies of astrophysical interest". United States. doi:10.1103/PHYSREVC.75.015803.
@article{osti_20990980,
title = {Expectations for {sup 12}C and {sup 16}O induced fusion cross sections at energies of astrophysical interest},
author = {Jiang, C. L. and Rehm, K. E. and Back, B. B. and Janssens, R. V. F.},
abstractNote = {The extrapolations of cross sections for fusion reactions involving {sup 12}C and {sup 16}O nuclei down to energies relevant for explosive stellar burning have been reexamined. Based on a systematic study of fusion in heavier systems, it is expected that a suppression of the fusion process will also be present in these light heavy-ion systems at extreme sub-barrier energies due to the saturation properties of nuclear matter. Previous phenomenological extrapolations of the S factor for light heavy-ion fusion based on optical model calculations may therefore have overestimated the corresponding reaction rates. A new ''recipe'' is proposed to extrapolate S factors for light heavy-ion reactions to low energies taking the hindrance behavior into account. It is based on a fit to the logarithmic derivative of the experimental cross section which is much less sensitive to overall normalization discrepancies between different data sets than other approaches. This method, therefore, represents a significant improvement over other extrapolations. The impact on the astrophysical reaction rates is discussed.},
doi = {10.1103/PHYSREVC.75.015803},
journal = {Physical Review. C, Nuclear Physics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • The extrapolations of cross sections for fusion reactions involving {sup 12}C and {sup 16}O nuclei down to energies relevant for explosive stellar burning have been reexamined. Based on a systematic study of fusion in heavier systems, it is expected that a suppression of the fusion process will also be present in these light heavy-ion systems at extreme sub-barrier energies due to the saturation properties of nuclear matter. Previous phenomenological extrapolations of the S factor for light heavy-ion fusion based on optical model calculations may therefore have overestimated the corresponding reaction rates. A new 'recipe' is proposed to extrapolate S factorsmore » for light heavy-ion reactions to low energies taking the hindrance behavior into account. It is based on a fit to the logarithmic derivative of the experimental cross section which is much less sensitive to overall normalization discrepancies between different data sets than other approaches. This method, therefore, represents a significant improvement over other extrapolations. The impact on the astrophysical reaction rates is discussed.« less
  • The {sup 12}C(α,γ){sup 16}O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for S{sub E1}(300) and 7 to 120more » keVb for S{sub E2}(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi- elastic α scattering on {sup 12}C, α-transfer reactions to {sup 16}O, and {sup 16}N decay are usually included in the analysis. Here the β-delayed α decay of {sup 16}N is used to infer information on the {sup 12}C(α,γ){sup 16}O reaction and a new experimental technique is suggested.« less
  • Fusion cross sections are calculated in the time-dependent Hartree-Fock approximation, for the systems /sup 18/O + /sup 12/C and /sup 16/O + /sup 12/C. Although the experimentally observed fluctuations in the /sup 16/O + /sup 12/C fusion cross section are not reproduced in the calculations, the results are otherwise in good agreement with experiment, except at the highest energies studied.