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Title: Measurement of the Cascade Transition via the First Excited State of {sup 16}O in the {sup 12}C({alpha},{gamma}){sup 16}O Reaction, and Its S Factor in Stellar Helium Burning

Abstract

Radiative {alpha}-particle capture into the first excited, J{sup {pi}}=0{sup +} state of {sup 16}O at 6.049 MeV excitation energy has rarely been discussed as contributing to the {sup 12}C({alpha},{gamma}){sup 16}O reaction cross section due to experimental difficulties in observing this transition. We report here measurements of this radiative capture in {sup 12}C({alpha},{gamma}){sup 16}O for center-of-mass energies of E=2.22 MeV to 5.42 MeV at the DRAGON recoil separator. To determine cross sections, the acceptance of the recoil separator has been simulated in GEANT as well as measured directly. The transition strength between resonances has been identified in R-matrix fits as resulting both from E2 contributions as well as E1 radiative capture. Details of the extrapolation of the total cross section to low energies are then discussed [S{sub 6.0}(300)=25{sub -15}{sup +16} keV b] showing that this transition is likely the most important cascade contribution for {sup 12}C({alpha},{gamma}){sup 16}O.

Authors:
;  [1]; ; ; ; ; ; ; ; ;  [2];  [3]; ; ; ; ;  [4]; ;  [5];  [6]
  1. Ohio University, Athens, Ohio (United States)
  2. TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T 2A3 (Canada)
  3. University of Konstanz, Department of Physics (Germany)
  4. Simon Fraser University, Burnaby, British Columbia (Canada)
  5. McMaster University, Hamilton, Ontario (Canada)
  6. China Institute of Atomic Energy, Beijing (China)
Publication Date:
OSTI Identifier:
20861476
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 97; Journal Issue: 24; Other Information: DOI: 10.1103/PhysRevLett.97.242503; (c) 2006 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; ALPHA PARTICLES; ALPHA REACTIONS; CAPTURE; CARBON 12 TARGET; CENTER-OF-MASS SYSTEM; EXCITATION; EXCITED STATES; EXTRAPOLATION; GAMMA RADIATION; HELIUM BURNING; MEV RANGE 01-10; OXYGEN 16; R MATRIX; STAR EVOLUTION; TOTAL CROSS SECTIONS

Citation Formats

Matei, C., Brune, C. R., Buchmann, L., Hutcheon, D. A., Caggiano, J., Laird, A., Li, ZH., Olin, A., Ottewell, D., Ruprecht, G., Trinczek, M., Hannes, W. R., Ruiz, C., D'Auria, J., Lamey, M., Vockenhuber, C., Wrede, C., Chen, A. A., Pearson, J., and Liu, WP. Measurement of the Cascade Transition via the First Excited State of {sup 16}O in the {sup 12}C({alpha},{gamma}){sup 16}O Reaction, and Its S Factor in Stellar Helium Burning. United States: N. p., 2006. Web. doi:10.1103/PHYSREVLETT.97.242503.
Matei, C., Brune, C. R., Buchmann, L., Hutcheon, D. A., Caggiano, J., Laird, A., Li, ZH., Olin, A., Ottewell, D., Ruprecht, G., Trinczek, M., Hannes, W. R., Ruiz, C., D'Auria, J., Lamey, M., Vockenhuber, C., Wrede, C., Chen, A. A., Pearson, J., & Liu, WP. Measurement of the Cascade Transition via the First Excited State of {sup 16}O in the {sup 12}C({alpha},{gamma}){sup 16}O Reaction, and Its S Factor in Stellar Helium Burning. United States. doi:10.1103/PHYSREVLETT.97.242503.
Matei, C., Brune, C. R., Buchmann, L., Hutcheon, D. A., Caggiano, J., Laird, A., Li, ZH., Olin, A., Ottewell, D., Ruprecht, G., Trinczek, M., Hannes, W. R., Ruiz, C., D'Auria, J., Lamey, M., Vockenhuber, C., Wrede, C., Chen, A. A., Pearson, J., and Liu, WP. Fri . "Measurement of the Cascade Transition via the First Excited State of {sup 16}O in the {sup 12}C({alpha},{gamma}){sup 16}O Reaction, and Its S Factor in Stellar Helium Burning". United States. doi:10.1103/PHYSREVLETT.97.242503.
@article{osti_20861476,
title = {Measurement of the Cascade Transition via the First Excited State of {sup 16}O in the {sup 12}C({alpha},{gamma}){sup 16}O Reaction, and Its S Factor in Stellar Helium Burning},
author = {Matei, C. and Brune, C. R. and Buchmann, L. and Hutcheon, D. A. and Caggiano, J. and Laird, A. and Li, ZH. and Olin, A. and Ottewell, D. and Ruprecht, G. and Trinczek, M. and Hannes, W. R. and Ruiz, C. and D'Auria, J. and Lamey, M. and Vockenhuber, C. and Wrede, C. and Chen, A. A. and Pearson, J. and Liu, WP.},
abstractNote = {Radiative {alpha}-particle capture into the first excited, J{sup {pi}}=0{sup +} state of {sup 16}O at 6.049 MeV excitation energy has rarely been discussed as contributing to the {sup 12}C({alpha},{gamma}){sup 16}O reaction cross section due to experimental difficulties in observing this transition. We report here measurements of this radiative capture in {sup 12}C({alpha},{gamma}){sup 16}O for center-of-mass energies of E=2.22 MeV to 5.42 MeV at the DRAGON recoil separator. To determine cross sections, the acceptance of the recoil separator has been simulated in GEANT as well as measured directly. The transition strength between resonances has been identified in R-matrix fits as resulting both from E2 contributions as well as E1 radiative capture. Details of the extrapolation of the total cross section to low energies are then discussed [S{sub 6.0}(300)=25{sub -15}{sup +16} keV b] showing that this transition is likely the most important cascade contribution for {sup 12}C({alpha},{gamma}){sup 16}O.},
doi = {10.1103/PHYSREVLETT.97.242503},
journal = {Physical Review Letters},
number = 24,
volume = 97,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The {sup 12}C({alpha},{gamma}){sup 16}O reaction is of great importance for the understanding the nuclear synthesis and explosion mechanism of the supernova. The cross section at the relevant stellar burning energies, around 300 keV, is dominated by the sub-threshold resonances. The {sup 16}N {beta}-delayed {alpha} decay data provide the most sensitive constrain on this sub-threshold resonance. Using twin-ionization chambers, we have measured the {alpha} particles and {sup 12}C recoil nuclei in coincidence. The spectrum has been fitted together with the published {sup 12}C({alpha},{gamma}){sup 16}O data and the elastic scattering phase shift data using R-matrix. The S{sub E1} factor at 300 keVmore » has been determined as 73{+-}21 keVb.« less
  • The {sup 12}C({alpha},{gamma}){sup 16}O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of {sup 12}C({alpha},{gamma}){sup 16}O still highly uncertain. The extrapolation of the measured cross sections to stellar energies (E{approx}300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 and 7.12 MeV of {sup 16}O. In order to further investigate the contribution of these two-subthreshold resonances to the {sup 12}C({alpha},{gamma}){sup 16}O cross section, we performed a new determination of the {alpha}-reduced widths via a measurement of the transfer reaction {supmore » 12}C({sup 7}Li,t){sup 16}O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections will be presented as well as the obtained spectroscopic factors and the {alpha}-reduced widths.« less
  • A new measurement of the {beta}-delayed {alpha} decay of {sup 16}N has been performed using a set of high efficiency ionization chambers. Sources were made by implantation of a {sup 16} beam, yielding very clean {alpha} spectra down to energies as low as 400 keV. Our data are in good agreement with earlier results. For the S factor SE1, we obtain a value of 74{+-}21 keV b. In spite of improvements in the measurement, the error in SE1 remains relatively large because of the correlations among the fit parameters and the uncertainties inherent to the extrapolation.