Trojan Horse Investigation for AGB Stellar Nucleosynthesis

Asymptotic Giant Branch (AGB) stars are among the most important astrophysical sites influencing the nucleosynthesis and the chemical abundances in the Universe. From a pure nuclear point of view, several processes take part during this peculiar stage of stellar evolution thus requiring detailed experimental cross section measurements. Here, we report on the most recent results achieved via the application of the Trojan Horse Method (THM) and Asymptotic Normalization Coefficient (ANC) indirect techniques, discussing the details of the experimental procedure and the deduced reaction rates. In addition, we report also on the on going studies of interest for AGB nucleosynthesis

Trojan Horse Method experiments with radioactive ion beams

The Trojan Horse Method (THM) is an indirect method that allows to get information about a two body reaction cross-section even at very low energy, avoiding the suppression effects due to the presence of the Coulomb barrier. The method requires a very accurate measurement of a three body reaction in order to reconstruct the whole kinematics and discriminate among different reaction mechanisms that can populate the same final state. These requirements hardly match with the typical low intensity and large divergence of radioactive ion beams (RIBs), and experimental improvements are mandatory for the applicability of the method. The first reaction induced by a radio activeion beam studied by applying the THM was the 18F(p,α)15O. Two experiments were performed in two different laboratories and using different experimental set-ups. The two experiments will be discussed and some results will be presented

The 10B(p,α)7Be S(E)-factor from 5 keV to 1.5 MeV using the Trojan Horse Method

The 10 B(p, α ) 7 Be reaction is the main responsible for the 10 B destruction in stellar interior [1]. In such environments this p-capture process occurs at a Gamow energy of 10 keV and takes places mainly through a resonant state (Ex = 8.701 MeV) of the compound 11 C nucleus. Thus a resonance right in the region of the Gamow peak is expected to significantly influence the behavior of the astrophysical S(E)-factor. The 10 B(p, α ) 7 Be reaction was studied via the Trojan Horse Method (THM) applied to the 2 H( 10 B, α 7 Be)n in order to extract the astrophysical S(E)-factor in a wide energy range from 5 keV to 1.5 MeV

Study of the 19^{19}F(p,α\alpha)16^{16}O reaction through the Trojan Horse Method and its astrophysical enviroment

Fluorine nucleosynthesis takes place in the hydrogen-helium intershell region of Asymptotic Giant Branch (AGB) stars and in the same region also the $s$ elements are produced. Because fluorine is produced in the He-intershell and then dredged up to the surface together with $s$ process elements, its abundance is used as probe for AGB models and nucleosynthesis and is one of the most important input parameters for an analysis of $s$ process in AGB star conditions. The problem is that current models fail to explain the highest F enhancements found in the low-mass AGB stars. A possible way to explain this abundance found in AGB star envelopes might be provided by a revision of the uncertainties in the nuclear reaction rates involved in the synthesis of this nuclide in these stars. In particular, The $^{19}$F(p,$\alpha$)$^{16}$O reaction is the main destruction channel of fluorine at the bottom of the convective envelope in AGB stars, where it can experience temperatures large enough to determine its destruction, owing to extra-mixing processes. Because of the Coulomb barrier, measurements available in the literature do not have access to the energy region of astrophysical interest, corresponding to the Gamow peak (E$_{c.m.}$ = 38 keV). Direct measurements of the cross section stop at about 500 keV for the $\alpha_0$ channel (with $^{16}$O being left in its ground state following $^{20}$Ne decay), thus the astrophysical factor was then extrapolated to low energies assuming a non resonant energy trend. In the case of extra-mixing phenomena, which are characterized by a maximum temperature of about 10$^7$ K, the energy region below 500 keV is of key importance, thus requiring further and accurate investigations to evaluate the contribution of possible resonances, which could significantly enhance the reaction rate at such low temperatures. So, a new experimental study through the Trojan Horse Method (THM) is important because the method is particulary suited for the study of low-enegy resonances in the case of charged particle induced reactions. It is an experimental indirect technique which selects the quasi-free contribution of an appropriate three-body reaction performed at energies well above the Coulomb barrier, to extract a charged-particle two-body cross section at astrophysical energies free from coulomb suppression. Two experimental runs were performed using the THM, extracting the quasi-free contribution to the $^2$H($^{19}$F,$\alpha$$^{16}$O)n three-body reaction. In this work I focused on the second run especially because of the improved angular and energy resolution allowed to draw accurate quantitative conclusions from the data for the $\alpha_0$ channel. The measurement was performed at the Laboratori Nazionali di Legnaro in July 2012 where the Tandem accelerator provided a 55 MeV $^{19}$F beam which impinged onto CD$_2$ targets. The experimental setup consisted of a telescope devoted to oxygen detection, made up of an ionization chamber and a silicon position sensitive detector (PSD) on one side with respect to the beam direction and one additional PSD on the opposite side for coincident detection of the $\alpha$ particles. In the beginning of the experimental work, I described the reason leading to the choice of the three-body reaction, of the beam energy, of the setup and of the detection angles. After the off-line analysis in which I widely described the detector calibration, the three-body reaction channel selection, the study of reaction mechanism and the selection of the quasi-free contribution are discussed. Finally the cross-section reaction are extracted and compared with the available direct measurement. The analysis of the $\alpha_0$ channel shows the presence of resonant structure never observed before that could lead to a significant increase in the reaction rate at astrophysical temperatures, with important consequences for stellar nucleosynthesis

Nuclear Physics in Stellar Lifestyles with the Trojan Horse Method

The Trojan Horse Method is an indirect technique to measure nuclear reactions of astrophysical relevance at the energies of interest, free of Coulomb suppression and electron screening effects. Its basic features in the framework of the theory of direct reactions will be discussed and the physics case of the 12C+12C fusion will be addressed

Nuclear Physics in Stellar Lifestyles with the Trojan Horse Method

The Trojan Horse Method is an indirect technique to measure nuclear reactions of astrophysical relevance at the energies of interest, free of Coulomb suppression and electron screening effects. Its basic features in the framework of the theory of direct reactions will be discussed and the physics case of the 12C+12C fusion will be addressed

The Trojan Horse Method in Nuclear Astrophysics

The Trojan Horse Method (THM) represents the indirect way to measure reactions between charged particles at astrophysical energies. This is done by measuring the quasi free cross section of a suitable three body process. The basic features of the THM will be presented together with some applications to demonstrate its practical use

The Trojan Horse Method in Nuclear Astrophysics

The Trojan Horse Method (THM) represents the indirect way to measure reactions between charged particles at astrophysical energies. This is done by measuring the quasi free cross section of a suitable three body process. The basic features of the THM will be presented together with some applications to demonstrate its practical use

Trojan Horse Method experiments with radioactive ion beams

The Trojan Horse Method (THM) is an indirect method that allows to get information about a two body reaction cross-section even at very low energy, avoiding the suppression effects due to the presence of the Coulomb barrier. The method requires a very accurate measurement of a three body reaction in order to reconstruct the whole kinematics and discriminate among different reaction mechanisms that can populate the same final state. These requirements hardly match with the typical low intensity and large divergence of radioactive ion beams (RIBs), and experimental improvements are mandatory for the applicability of the method. The first reaction induced by a radio activeion beam studied by applying the THM was the 18F(p,α)15O. Two experiments were performed in two different laboratories and using different experimental set-ups. The two experiments will be discussed and some results will be presented