Search

The Asymptotic Normalization Coefficient (ANC) method, has proven to be useful in retrieving the direct part of the radiative capture cross section for a number of reactions of astrophysical interest. In this work, some of the latest results obtained by the AsFin2 group of the LSN-INFN (Catania) and the OJR of the NPI (Řež) will be briefly discussed. [ABSTRACT FROM AUTHOR]

We attempted to determine the astrophysical S-factor of the direct part of the 18O(p, γ)19F capture by the indirect method of asymptotic normalization coefficients (ANC). We measured the differential cross section of the transfer reaction 18O(3He, d)19F at a 3He energy of 24.6 MeV. The measurement was realized on the cyclotron of the NPI in Řež, Czech Republic, with the gas target consisting of the high purity 18O (99.9 %). The reaction products were measured by eight ∆E-E telescopes composed from thin and thick silicon surface-barrier detectors. The parameters of the optical model for the input channel were deduced by means of the code ECIS and the analysis of transfer reactions to 12 levels of the 19F nucleus up to 8.014 MeV was made by the code FRESCO. The deduced ANCs were then used to specify the direct contribution to the 18O(p, γ)19F capture process and were compared with the mutually different results of two works. [ABSTRACT FROM AUTHOR]

Boron abundances in stellar atmospheres, as well as berillium and lithium ones, can give useful hints for non-standard transport processes discrimination in stars. They can also be relevant for understanding several astrophysical processes (e.g. primordial nucleosynthesis and spallation reactions in ISM). A comprehensive study of Li Be B abundances can therefore confirm or not the presence of non-standard mixing processes in stellar envelopes. For this reason nuclear processes producing or depleting boron isotope abundance need to be studied at astrophysical energies. The 10B(p,α)7Be reaction has been studied by means of the Trojan Horse Method. The Trojan Horse Method was thus applied to the 10B(d,α 7Be)n reaction, studied at 24 MeV. The obtained results will be discussed. [ABSTRACT FROM AUTHOR]

The Trojan Horse Method (THM) was applied to the 3He+6Li interaction in order to investigate the quasi-free 6Li(d,α)4He reaction. The experiment was performed at 17 MeV at the Cyclotron Institute of the Czech Academy of Science. The extracted 6Li(d,α)4He quasi-free cross-section was compared with the behavior of direct data. A good agreement between data sets shows up throughout the energy range investigated, providing a very important validity test of the pole approximation for the THM above the Coulomb barrier. [ABSTRACT FROM AUTHOR]

In order to understand primordial and stellar nucleosynthesis, we have studied 2H(d,p)3H reaction at 0.4 MeV down to astrophysical energies. Knowledge of its S-factor is interesting also to plan reactions for fusion reactors to produce energy. The 2H(d,p)H reaction has been studied through the Trojan Horse Method applied to the three-body reaction 2H(He,pt)H, at beam energy of 17 MeV. Once selection of protons and tritons detected in coincidence and the selection of quasi-free events, the obtained S-factor is compared with direct measurements. Such data are in agreement with the direct ones and a pole invariance test has been obtained comparing the present results with another 2H(d,p)3H THM measurements, where a different spectator particle was employed. [ABSTRACT FROM AUTHOR]

Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short-lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T-REX are discussed. [ABSTRACT FROM AUTHOR]

The use of quasi-free reactions in studying nuclear reactions between charged particles of astrophysical interest has received much attention over the last two decades. The Trojan Horse Method is based on this approach and it has been used to study a number of reactions relevant for Nuclear Astrophysics. Recently we applied this method to the study of nuclear reactions that involve radioactive species, namely to the study of the 18F+p→15O+α process at temperatures corresponding to the energies available in the classical novae scenario. Quasi-free reactions can also be exploited to study processes induced by neutrons. This technique is particularly interesting when applied to reaction induced by neutrons on unstable short-lived nuclei. Such processes are very important in the nucleosynthesis of elements in the sand r-processes scenarios and this technique can give hints for solving key questions in nuclear astrophysics where direct measurements are practically impossible. [ABSTRACT FROM AUTHOR]

We address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique to determine the astrophysical factor for the 13C(α, n)16O reaction which is one of the neutron generators for the s processes in the AGB stars. The TH method is unique indirect technique allowing one to measure astrophysical rearrangement reactions down to astrophysically relevant energies. Using a simple model, we demonstrate that off-energy-shell and Coulomb effects in the entry channel and the final state nuclear interaction do not change the energy dependence of the astrophysical factor extracted from the TH reaction. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The astrophysically relevant 7Li+p→α+α reaction was investigated via the THM by selecting the quasi-free contribution to the measured 3He+7Li→α+α+d three-body process. This investigation is mainly aimed at testing the validity of the pole approximation in the THM against the bound structure of the Trojan-horse nucleus. The three-body experiment was performed at 33 MeV, corresponding to a 7Li-p relative energy ranging from 0.2 to 7 MeV. The quasi-free 7Li+p cross-section was compared with the free reaction cross-section as well as with indirect data from a previous THM experiment. The good agreement between data sets throughout the energy range investigated provided a very important validity test of the pole approximation for the THM. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The 19F(p,α)16O reaction is an important fluorine destruction channel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogendeficient post-AGB star nucleosynthesis. So far, available direct measurements do not reach the energy region of astrophysical interest (Ecm ∼ 300 keV), because of the hindrance effect of the Coulomb barrier. The Trojan Horse (TH) method was thus used to access this energy region, by extracting the quasi-free contribution to the 2H(19F,α16O)n reaction. The TH measurement of the α0 channel, which is the dominant one at such energies, shows the presence of resonant structures not observed before that cause an increase of the reaction rate at astrophysical temperatures up to a factor of 1.7, with potential important consequences for stellar nucleosynthesis. [ABSTRACT FROM AUTHOR]

Because of the still present uncertainties on its rate, the 17O(p,α)14N is one of the most important reaction to be studied in order to get more information about the fate of 17O in different astrophysical scenarios. The preliminary study of the three-body reaction 2H(17O,α14N)n is presented here as a first stage of the indirect study of this important 17O(p,α)14N reaction through the Trojan Horse Method (THM) [ABSTRACT FROM AUTHOR]

The reaction cross section for the direct radiative proton capture on the the drip line nucleus 12N—12N(p,γ)13O—was studied at the Cyclotron Institute/Texas A&M University using the indirect asymptotic normalization coefficient method. This reaction is important in the hot pp chain nuclear burning processes in hydrogen-rich massive objects (Population III stars). The astrophysical S-factor of the direct proton capture was determined at zero energy yielding a value of SDC1–12 = 0.31(5) keV b. Interference between direct and resonant capture leads to a further enhancement of a factor of two. [ABSTRACT FROM AUTHOR]