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The ^(12)C(α, γ)^(16)O reaction and stellar helium burning

Dyer, P. and Barnes, C. A. (1974) The ^(12)C(α, γ)^(16)O reaction and stellar helium burning. Nuclear Physics A, 233 (2). pp. 495-520. ISSN 0375-9474. doi:10.1016/0375-9474(74)90470-9.

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The cross section for the reaction ^(12)C(α, γ)^(16)O has been measured for a range of c.m. energies extending from 1.41 MeV to 2.94 MeV, by using ^(12)C targets of high isotopic purity, large NaI(T1) crystals, and the time-of-flight technique for the suppression of prompt neutron background and time-independent background. Gamma-ray angular distributions were measured at c.m. energies of 2.18, 2.42, 2.56 and 2.83 MeV. By means of theoretical fits, which include the coherent effects of the 1^− states of ^(16)O at 7.12 MeV, 9.60 MeV, and those at higher energies, the electric-dipole portion of the cross section at astrophysically relevant energies has been determined. A three-level R-matrix parametrization of the data yields an S-factor at E_(c.m.) = 0.3 MeV, S(0.3 MeV) = 0.14^(+0.14)_(−0.12) MeV · b. A “hybrid” R-matrix optical-m parameterization yields S(0.3 MeV) = 0.08^(+0.05)_(−0.04) MeV · b. This S-factor is of crucial importance in determining the abundances of ^(12)C and ^(16)O at the end of helium burning in stars.

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Additional Information:© 1974 North-Holland Publishing Co. Received 15 July 1974. Supported in part by the National Science Foundation [GP-280271]. We wish to thank Dr. Eileen Hess of DHOM Products Ltd. for converting the ORNL amorphous carbon to methyl iodide, and we are especially indebted to Dr. N. A. Matwiyoff and Dr. B. B. Mclnteer of the Los Alamos Scientific Laboratory for supplying the highly enriched ^(12)C-methanol without which the lowest cross sections could not have been measured. We are grateful to Prof. T. A. Tombrello for discussions of the theoretical aspects of this work, and to Drs. D. C. Weisser, J. F. Morgan and D. R. Thompson for developing the three-level R-matrix computer program which we have used in the present work. We would also like to thank Drs. Weisser and Morgan for their contributions to the time-of-flight technique, Dr. H.-B. Mak for developing the fast amplifiers used to pick off the beam-pulse signals, and Dr. M. R. Dwarakanath for his work on the pulsed-beam source for the 3 MeV accelerator. We have valued highly the continuing encouragement of Prof. William A. Fowler, and many other colleagues in the astrophysical community, throughout these protracted and difficult measurements. One of us (C. A. B.) is grateful to the Nordisk Institut for Teoretisk Atomfysik for their hospitality and partial support during the preparation of this paper.
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Official Citation:P. Dyer, C.A. Barnes, The 12C(α, γ)16O reaction and stellar helium burning, Nuclear Physics A, Volume 233, Issue 2, 18 November 1974, Pages 495-520, ISSN 0375-9474, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60137
Deposited By: Ruth Sustaita
Deposited On:11 Sep 2015 17:32
Last Modified:10 Nov 2021 22:30

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