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Published August 1, 1994 | public
Journal Article Open

Constraints on the low-energy E1 cross section of 12C(α,γ)16O from the β-delayed α spectrum of 16N

Abstract

The shape of the low-energy part of the β-delayed α-particle spectrum of 16N is very sensitive to the α+12C reduced width of the 7.117 MeV subthreshold state of 16O. This state, in turn, dominates the low-energy p-wave capture amplitude of the astrophysically important 12C(α,γ)16O reaction. The α spectrum following the decay of 16N has been measured by producing a low-energy 16N14N+ beam with the TRIUMF isotope separator TISOL, stopping the molecular ions in a foil, and counting the α particles and 12C recoil nuclei in coincidence, in thin surface-barrier detectors. In addition to obtaining the α spectrum, this procedure determines the complete detector response including the low-energy tail. The spectrum, which contains more than 106 events, has been fitted by R- and K-matrix parametrizations which include the measured 12C(α,γ)16O cross section and the measured α+12C elastic scattering phase shifts. The model space appropriate for these parametrizations has been investigated. For SE1(300), the E1 part of the astrophysical S factor for the 12C(α,γ)16O reaction at Ec.m.=300 keV, values of 79±21 and 82±26 keV b have been derived from the R- and K-matrix fits, respectively.

Additional Information

©1994 The American Physical Society. Received 16 March 1994. We would like to express our appreciation to J. Humblet for extensive help and advice given to us in the development of our K-matrix analysis. This contribution proved to be invaluable. We wish to thank E.W. Vogt for valuable discussions concerning the R-matrix analysis. We also wish to thank H. Biegenzein, D. Jones, P. Machule, H. Sprenger, A. Wilson, and G. Sheffer for help with the technical aspects of the experiment, and D. Diel and P.W. Green for assistance with the data acquisition system. Our special thanks go to Teleglobe Canada for the donation of a 6 GHz amplifier, without which the operation of the ECR source at TISOL and this experiment would have been impossible. The help of summer students A. Chen, J. Chen, and M. Trinczek is gratefully acknowledged. One of the authors (R.E.A.) wishes to express his thanks to the Kellogg Radiation Laboratory at Caltech for their hospitality during the early stages of the experiment. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada, by the National Science Foundation (Grant No. PHY-91-15574), and by TRIUMF. See also: Erratum: R. E. Azuma, L. Buchmann, F. C. Barker, C. A. Barnes, J. M. D'Auria, M. Dombsky, U. Giesen, K. P. Jackson, J. D. King, R. G. Korteling, P. McNeely, J. Powell, G. Roy, J. Vincent, T. R. Wang, S. S. Wong, and P. R. Wrean, Constraints on the low-energy E1 cross section of 12C(α,γ)16O from the β-delayed α spectrum of 16N [Phys. Rev. C 50, 1194 (1994)], Phys. Rev. C 56, 1655 (1997).

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