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Title: 18F({alpha},p)21Ne Reaction: Neutron Source For r-Process In Supernovae

Abstract

The reaction rate of 18F({alpha},p)21Ne has been studied using the inverse reaction 21Ne(p,{alpha})18F. This has been measured by the activation method in the energy range of the relevant Gamow window. Experimental results will be discussed and compared with the results of Hauser-Feshbach calculations and previous measurements.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;  [1];  [2]
  1. Department of Physics, University of Notre Dame, Notre Dame, IN (United States)
  2. Dynamitron Tandem Laboratory, Ruhr-Universitaet, Bochum (Germany)
Publication Date:
OSTI Identifier:
20798363
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 819; Journal Issue: 1; Conference: 12. international symposium on capture gamma-ray spectroscopy and related topics, Notre Dame, IN (United States), 4-9 Sep 2005; Other Information: DOI: 10.1063/1.2187927; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ALPHA REACTIONS; FLUORINE 18 TARGET; NEON 21; NEUTRON SOURCES; NUCLEAR REACTION KINETICS; NUCLEOSYNTHESIS; R PROCESS; SUPERNOVAE

Citation Formats

Lee, H.-Y., Beard, M., Couder, M., Couture, A., Goerres, J., Lamm, L., LeBlanc, P., O'Brien, S., Palumbo, A., Stech, E., Strandberg, E., Tan, W., Ugalde, C., Wiescher, M., and Becker, H.-W.. 18F({alpha},p)21Ne Reaction: Neutron Source For r-Process In Supernovae. United States: N. p., 2006. Web. doi:10.1063/1.2187927.
Lee, H.-Y., Beard, M., Couder, M., Couture, A., Goerres, J., Lamm, L., LeBlanc, P., O'Brien, S., Palumbo, A., Stech, E., Strandberg, E., Tan, W., Ugalde, C., Wiescher, M., & Becker, H.-W.. 18F({alpha},p)21Ne Reaction: Neutron Source For r-Process In Supernovae. United States. doi:10.1063/1.2187927.
Lee, H.-Y., Beard, M., Couder, M., Couture, A., Goerres, J., Lamm, L., LeBlanc, P., O'Brien, S., Palumbo, A., Stech, E., Strandberg, E., Tan, W., Ugalde, C., Wiescher, M., and Becker, H.-W.. Mon . "18F({alpha},p)21Ne Reaction: Neutron Source For r-Process In Supernovae". United States. doi:10.1063/1.2187927.
@article{osti_20798363,
title = {18F({alpha},p)21Ne Reaction: Neutron Source For r-Process In Supernovae},
author = {Lee, H.-Y. and Beard, M. and Couder, M. and Couture, A. and Goerres, J. and Lamm, L. and LeBlanc, P. and O'Brien, S. and Palumbo, A. and Stech, E. and Strandberg, E. and Tan, W. and Ugalde, C. and Wiescher, M. and Becker, H.-W.},
abstractNote = {The reaction rate of 18F({alpha},p)21Ne has been studied using the inverse reaction 21Ne(p,{alpha})18F. This has been measured by the activation method in the energy range of the relevant Gamow window. Experimental results will be discussed and compared with the results of Hauser-Feshbach calculations and previous measurements.},
doi = {10.1063/1.2187927},
journal = {AIP Conference Proceedings},
number = 1,
volume = 819,
place = {United States},
year = {Mon Mar 13 00:00:00 EST 2006},
month = {Mon Mar 13 00:00:00 EST 2006}
}
  • At the high temperature and density conditions of hot or explosive helium burning, the {sup 18}F({alpha},p){sup 21}Ne reaction may compete successfully wilh the {sup 18}F({beta}{sup +}{nu}) decay. This suggesls {sup 21}Ne({alpha},n) as an alternative neutron source in Ihe r-process. We have determined the total cross section of the {sup 18}F({alpha},p){sup 21}Ne reaction by studying the time-reverse reaction {sup 21}Ne(p,{alpha}){sup 18}F. Using the activation technique, the total reaction yield was measured in the proton beam energy range of 2.3-4.0 MeV, which corresponds to energies of 0.5-2.1 MeV in the {sup 18}F + {alpha} system. The resulting yield curve was analyzed inmore » terms of the thick target formalism and the R-matrix theory. The reaction rate was deduced experimentally for the first time for the temperature of 0.1 < T{sub 9} < I. The experimemal reaction rate was compared with Hauser-Feshbach predictions. The astrophysical implications of the new rate are discussed.« less
  • A good understanding of the level structure of 19Ne around the proton threshold is critical to estimating the destruction of long-lived 18F in novae. Here we report the properties of levels in 19Ne in the excitation energy range of 6.9 Ex 8.4 MeV studied via the proton-transfer 18F(d, n)Ne reaction at the Holifield Radioactive Ion Beam Facility. The populated 19Ne levels decay by breakup into p + 18F and + 15O particles. The results presented in this manuscript are those of levels that are simultaneously observed from the breakup into both channels. An s-wave state is observed at 1468 keVmore » above the proton threshold, which is a potential candidate for a predicted broad J = 1/2+ state. The proton and partial widths are deduced to be p = 228 50 keV and = 130 30 keV for this state.« less
  • The {sup 13}C({alpha},n){sup 16}O reaction constitutes the dominant neutron source for the main s process, which operates at a thermal energy of kT=8 keV. Since the cross section at stellar energies is very small, the reaction rate cannot be directly determined and has to be extrapolated from cross section results obtained at higher energies. To remove various discrepancies in the normalization of previous data sets and to subsequently improve the reliability of the extrapolation, we performed measurements of the {sup 13}C({alpha},n){sup 16}O reaction in the energy range E{sub c.m.}=320-700 keV. In addition, the double differential scattering cross section {sup 13}C({alpha},{alpha}){supmore » 13}C was measured in the energy range E{sub lab}=2.6-6.2 MeV for 28 angles. These data were used to constrain possible contributions from background resonances for a reliable extrapolation with the multichannel R-matrix code SAMMY. As a result, the uncertainties were significantly reduced, and a reaction rate of (4.6{+-}1.0)x10{sup -14} cm{sup 3}/moles at kT=8 keV (T=0.1x10{sup 9} K) was determined.« less
  • We have examined the results of shock heating of the helium zone in stars undergoing supernova explosions under a wide variety of temperatures and densities. We find that for peak temperatures near 4 x 10/sup 8/ K and peak densities near 10/sup 4/ g cm/sup -3/ the solar system r-process abundance curve can be reproduced. These conditions correspond to shock wave velocities of approximately 4000 km s/sup -1/ in the helium zone of an evolved star. The neutrons to drive the r-process are produced by /sup 13/C(..cap alpha.., n)/sup 16/O reactions. To produce a sufficient flux of neutrons over severalmore » seconds requires approximately 2% /sup 13/C by mass in the helium zone, and thus depends upon some type of mixing between the hydrogen-rich envelope and the helium zone prior to the supernova. We find that neither /sup 22/Ne nor /sup 18/O can provide a sufficient neutron flux in this type of environment. Our calculated fit to the solar system r-process curve is improved when the beta-decay rates of the heavy nuclei are increased by a factor of 5--10 over the rates using the gross theory, compatible with the recent results obtained by Klapdor et al. For reasonable mass ranges of supernova progenitors, a maximum of only 2.2 x 10/sup -5/ M/sub sun/ of r-process elements must be ejected per supernova to satisfy galactic nucleosynthesis requirements.« less
  • No abstract prepared.