Abstract
The 19F(ρ,α)16O reaction is an important fluorine destruction chan- nel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogen-deficient post-AGB star nucleosynthesis. At present, theoretical models overproduce F abundances in AGB stars with re-spect to the observed values, thus calling for further investigation of the nuclear reaction rates involved in the production and destruction of fluorine. In the last years, new direct and indirect measurements improved significantly the knowl- edge of 19F(ρ,α)16O cross section at deeply sub-Coulomb energies (below 0.8 MeV). However, those data are larger by a factor of 1.4 with respect the previ- ous data reported in the NACRE compilation in the energy region 0.6-0.8 MeV. Using the Large High resolution Array of Silicons for Astrophysics (LHASA), we performed a new direct measurement of the 19F(ρ,α)16O. The goal of this experiment is to reduce the uncertainties in the nuclear reaction rate of the 19F(ρ,α)16O reaction. Here, experimental details, the calibration procedure and angular distributions are presented.
Highlights
Experimental detailsThis experiment was performed at INFN - Laboratori Nazionali del Sud, Catania (Italy)
With s-process elements, its abundance is used as probe for asymptotic giant branch (AGB) models and nucleosynthesis and is one of the most important input parameters for the analysis of s-process in AGB star conditions [1,2,3]
Since the angular coverage of the experimental setup is approximately 15% of the total solid angle, the number of reactions is calculated by integrating the angular distribution for each energy
Summary
This experiment was performed at INFN - Laboratori Nazionali del Sud, Catania (Italy). The 15 MV Tandem Van der Graaff provided a 19F beam in the energy range from 9 up to 18.5 MeV with a spot size on target of 1 mm and intensities around 1 - 5 nA. Thin self-supported polyethylene targets (CH2) of about 100 μg/cm were placed at 90◦ with respect to the beam direction and were frequently changed to avoid degradation. In order to calculate the cross section, it is necessary to calculate the number of particles in the beam, the number of particles in the target and the number of reactions. Since the angular coverage of the experimental setup is approximately 15% of the total solid angle, the number of reactions is calculated by integrating the angular distribution for each energy.
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