40 research outputs found
Reaction rate for carbon burning in massive stars
Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5-4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate
Fusion measurements of 12C+12C at energies of astrophysical interest
The cross section of the 12C+12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of 12C+12C were successfully carried out with the Îł and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for 12C+12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques
How well do we understand the reaction rate of C burning?
Carbon burning plays a crucial role in stellar evolution, where this reaction is an important route for the production of heavier elements. A particle-Îł coincidence technique that minimizes the backgrounds to which this reaction is subject and provides reliable cross sections has been used at the Argonne National Laboratory to measure fusion cross-sections at deep sub-barrier energies in the 12C+12C system. The corresponding excitation function has been extracted down to a cross section of about 6 nb. This indicates the existence of a broad S-factor maximum for this system. Experimental results are presented and discussed
Reaction rate for carbon burning in massive stars
Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5-4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate
Isolement de mutants de tabac (Nicotiana tabacum) résistants à de fortes doses d'acides aminés à partir de cellules dérivées de protoplastes
*INRA, Unité de Génétique et d'Amélioration des Plantes, 78026 Versailles Cedex Diffusion du document : INRA, Unité de Génétique et d'Amélioration des Plantes, 78026 Versailles Cedex Diplôme : Dr. d'Universit
Preparation and fusion properties of protoplasts from mature pollen of Nicotiana tabacum
International audienc
Impact potentiel des techniques de biologie cellulaire et moleculaire pour l'amelioration des plantes
National audienc