Direct Capture Cross Section and the Ep=71 and 105 keV Resonances in the Ne22(p,γ)Na23 Reaction (original) (raw)
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Measurement of the 18Ne([alpha],p)21Na reaction rate : and its implications for Nuclear Astrophysics
1999
Experimental work has been carried out at Louvain-la-Neuve to study the reactions 13N(a, p) 160 and 18Ne(c, p) 21 Na in inverse kinematics with a gaseous helium target. The experimental method devised was tested using the reaction 13N(c, p) 160, as the cross section was calculable from data on the inverse reaction, 16 0(p, a) 13N [1-4]. This test experiment showed that the experimental error obtainable in the deduction of the resonance strengths, 'ys, was 30%, making the technique of practical use in the investigation of (cr, p) reactions of interest to Nuclear Astrophysics. The reaction 18Ne(c, p) 21 Na, which is important as a break-out mechanism from the hot CNO cycle into the rp-process during explosive hydrogen burning, has been investigated, and values for the resonance strengths have been extracted from the experimental data. A stellar reaction rate, based only upon the observed resonances, has been calculated and compared with theoretical predictions [5]. A good agreemen...
22Ne and23Na ejecta from intermediate-mass stars: the impact of the new LUNA rate for22Ne(p, γ)23Na
Monthly Notices of the Royal Astronomical Society, 2016
We investigate the impact of the new LUNA rate for the nuclear reaction 22 Ne(p, γ) 23 Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim, we use the PARSEC and COLIBRI codes to compute the complete evolution, from the premain sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range 3.0-6.0 M and metallicities Z i = 0.0005, 0.006 and 0.014. We find that the new LUNA measures have much reduced the nuclear uncertainties of the 22 Ne and 23 Na AGB ejecta that drop from factors of 10 to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of 23 Na, the uncertainties that still affect the 22 Ne and 23 Na AGB ejecta are mainly dominated by the evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anticorrelation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass-loss, third dredgeup, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anticorrelation and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available.
Physical Review C, 2003
The 22 Ne(␣,n) reaction is the main neutron source for neutron capture nucleosynthesis (s process͒ in massive stars and plays also a significant role for the s process in thermally pulsing asymptotic giant branch stars. In these scenarios, 22 Ne is produced by the reaction sequence 14 N(␣,␥) 18 F( ϩ ) 18 O(␣,␥) 22 Ne. While the first reaction is well understood, ␣ capture on 18 O was affected by considerable uncertainties. At the temperatures of stellar He burning, the reaction rate is determined by two resonances at ␣ energies of 470 and 566 keV. Since these resonances were not yet successfully measured, the rates had to be based on estimated resonance strengths. In the present work, the first direct measurement of the partial strengths of these extremely weak low-energy resonances is reported. The use of a high-efficiency segmented Ge detector in coincidence with bismuth germanate oxide counters covering a large solid angle led to a significantly improved experimental sensitivity, thus allowing for the clear identification of specific ␥ transitions. As a result, resonance strengths of 0.71Ϯ0.17 eV and 0.48Ϯ0.16 eV could be obtained for the 566-and 470-keV resonances, respectively. When compared to the previously reported upper limits of р1.7 eV, these results provide a reliable basis for the determination of the reaction rate during stellar He burning. Accordingly, these data reduce the uncertainties in the s process neutron balance.
The 19Ne(p,γ)20Na astrophysical reaction rate determined from measurements with a radioactive beam
Nuclear Physics A, 1997
The 19Ne(p,y)*% a as well as the '9Ne(d,n)2%a reaction have been studied in inverse kinematics using '"Ne radioactive beams. Upper and lower limits for the '9Ne(p,y)20Na astrophysical reaction rate have been deduced, for the first time on the basis of direct experimental data. It is concluded that the transition from the hot-CNO cycle to the rpprocess in explosive hydrogen burning is most likely governed by the preceeding "O(a,y)"Ne reaction.
Revision of the 15 N(p, γ ) 16 O reaction rate and oxygen abundance in H-burning zones
Astronomy & Astrophysics, 2011
Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ≃ 30 · 10 6 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the RGB (red giant branch) phase of the star or to the pollution of the primordial gas by an early population of massive AGB (asymptotic giant branch) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. Aims. The activation of this cycle depends on the rate of the 15 N(p,γ) 16 O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. Methods. We present a new measurement of the 15 N(p,γ) 16 O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 ·10 6 K and 780 ·10 6 K. This range includes the 15 N(p,γ) 16 O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. Results. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.
Revision of the 15N(p, gamma)16O reaction rate and oxygen abundance in H-burning zones
Astronomy & Astrophysics, 2011
Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ≃ 30 × 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. Aims: The activation of this cycle depends on the rate of the 15N(p, γ)16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. Methods: We present a new measurement of the 15N(p, γ)16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 × 106 K and 780 × 106 K. This range includes the 15N(p, γ)16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. Results: With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.
2017
D. W. Bardayan, K. A. Chipps, 3, 4 S. Ahn, J. C. Blackmon, S. Carmichael, U. Greife, K. L. Jones, J. José, 8 A. Kontos, R. L. Kozub, L. Linhardt, B. Manning, 12 M. Matoš, 4 P. D. O’Malley, S. Ota, S. D. Pain, W. A. Peters, 4 S. T. Pittman, 4 A. Sachs, K. T. Schmitt, 4, 12 M. S. Smith, and P. Thompson Physics Department, University of Notre Dame, Notre Dame, IN 46556, USA Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Physics Department, Colorado School of Mines, Golden, CO 80401, USA Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA Department of Physics and Astronomy, Northwestern Univeristy, Evanston, IL 60208, USA Departament de F́ısica, Universitat Politècnica de Catalunya, EEBE, E-08930 Barcelona, Spain Institut d’Estudis Espacials de Catalunya (IEEC), E-08034 Barcelona, Spain National Superconducting Cyclotron Laboratory, E...
The astrophysical implications of low-energy resonances in< sup> 22 Ne+ α
1993
The 22Ne(bLi, d) a-transfer reaction has been used to search for ol-unbound levels in ZhMg of importance for resonant cr-capture on 22Ne in stellar helium burning. To determine the resonance strengths of the observed states the 12Ne(a, n12"Mg reaction was investigated in the energy range between 600 and 900 keV. One resonance was identified and its strength determined. The astrophysical implications of the present results are discussed.