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Analysis of the total 12C(α,γ)16O cross section based on available angular distributions and other primary data

Buchmann, L. and Azuma, R. E. and Barnes, C. A. and Humblet, J. and Langanke, K. (1996) Analysis of the total 12C(α,γ)16O cross section based on available angular distributions and other primary data. Physical Review C, 54 (1). pp. 393-410. ISSN 0556-2813. doi:10.1103/PhysRevC.54.393.

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Because a knowledge of the 12C/16O ratio is crucial to the understanding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data from radiative α capture and elastic α scattering on 12C. Estimates of the total 12C(α,γ)16O rate at stellar energies are reported. In contrast with previous work, the analyses generally involve R- and K-matrix fits directly to the primary data, i.e., the energy- and angle-dependent differential yields, with all relevant partial waves fitted simultaneously (referred to here as surface fits). It is shown that, while the E1 part of the reaction is well constrained by a recent experiment on the β-delayed α-particle decay of 16N, only upper limits can be placed on the E2 ground state cross section factor which we take conservatively as SE2(300)<140 keV b. Simulations were then carried out to explore what kind of new data could lead to better restrictions on SE2(300). We find that improved elastic scattering data may be the best short-term candidate for such restrictions while significantly improving S(300) with new radiative capture data may require a longer-term effort. Theoretical models and estimates from α-transfer reactions for the E2 part of 12C(α,γ)16O are then discussed for comparison with the R- and K-matrix fits of the present work.

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Additional Information:©1996 The American Physical Society. Received 7 March 1996. The authors are grateful to the Queen’s University group, in particular Prof. H. Evans, for making their primary data available before publication. The authors also wish to thank Dr. U. Giesen and Dr. C. Iliadis for their contributions to discussions of transfer reactions. We also wish to express our gratitude to Prof. E.W. Vogt for his extensive discussions of R-matrix theory and transfer reactions. We would like to thank Prof. C. Rolfs of Bochum University for comments on the manuscript. The work has been partially supported by the Natural Sciences and Engineering Research Council of Canada, and by Grants Nos. PHY 94-20470 and PHY 94-12818 from the U.S. National Science Foundation.
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Deposited On:01 Apr 2008
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