Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........6f&link_type=abstract
Thesis (PHD). YALE UNIVERSITY , Source DAI-B 58/05, p. 2493, Nov 1997, 105 pages.
Astronomy and Astrophysics
Astrophysics
2
Nitrogen-16, Stellar Evolution
Scientific paper
The 12C(α,γ)16O reaction is of critical importance for understanding stellar evolution. During helium burning this reaction competes with the triple-alpha reaction that forms carbon. The final carbon/oxygen ratio at the end of this burning stage largely determines the final stages of the star. The beta-delayed alpha-emission of 16N (i.e. prompt alpha-particles emitted from excited states of 16O populated by the slow beta-decay of 16N) has been predicted to provide a constraint on the cross section of this reaction, but requires a high sensitivity (B.R. ~ 10-9) measurement. The low energy portion of the alpha-particle spectrum has been predicted to provide a sensitive means to deduce the reduced alpha-particle width of the bound 1- state in 16O. In the past few years three attempts have been made to constrain the p-wave component of this cross section using the beta-delayed alpha-particle emission of 16N. In this work we have made a high statistics measurement of this spectrum as a continuation of our earlier low statistics Yale-UConn experiment. We have improved the statistics by a factor of more than 5, the energy resolution by 20%, and we demonstrate an understanding of our line shape from known and measured quantities. Our newly measured spectrum is compared to the three previous high statistics experiments and found to be consistent with the experimental results from Mainz and Seattle and inconsistent with those from TRIUMF. Our discrepancy with the TRIUMF results is in the width of the primary peak, with the largest differences (nearly a factor of two) near the region of the interference minimum. This region of the spectrum determines the size of the f-wave contribution to the low energy secondary maximum. This is crucial as the magnitude of the p-wave contribution only is of importance to astrophysics due to the low energy (~300 keV) that stellar helium burning occurs in massive stars. We conclude that with the current data sets the p-wave S-factor of the 12C(α,γ)16O reaction cannot be determined at this stage with the accuracy (15-20%) required for the stellar evolution models developed by Woosley and Weaver.
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