Nuclear reactions within stars typically occur at energies significantly below 1 MeV. Consequently, the Coulomb barrier exponentially suppresses the cross section, reducing it to values as small as a ...few nanobarns for charged particles. This challenge in obtaining accurate input data for astrophysics has led to the introduction of indirect methods. Specifically, techniques such as ANC and THM have been employed to derive cross sections for reactions involving photons and charged particles in the exit channel, respectively, eliminating the need for extrapolation. The discussion delves into recent results from the application of these methods. For instance, the 6 Li( 3 He, d ) 7 Be measurement is utilized to deduce the ANC’s of the 3 He+ 4 He→ 7 Be and p + 6 Li→ 7 Be channels, along with their corresponding radiative-capture cross sections. Additionally, the THM measurement of the 27 Al( p, α ) 24 Mg cross section via the 2 H( 27 Al, α 24 Mg) n reaction is highlighted. In both cases, the cross section at astrophysical energies has been established with unprecedented accuracy.
The Trojan Horse Method (THM) represents an indirect path to determine the bare nucleus astrophysical
S
-factor for reactions among charged particles at astrophysical energies. This is achieved by ...measuring the quasi-free cross section of a suitable three-body process. The method is also suited to study neutron-induced reactions, especially in the case of radioactive ion beams. A comprehensive review of the theoretical as well as experimental features behind the THM is presented here. An overview is given of some recent applications to demonstrate the method's practical use for reactions that have a great impact on selected astrophysical scenarios.
In the last decades, many indirect methods have been developed to measure the cross section of nuclear reactions at the low energies interesting in many astrophysical scenarios. The Trojan Horse ...Method uses a three body reaction, involving by a strong clusterized nucleus, to infer information about a two body reaction of interest, selecting the events that proceed through the quasi-free reaction mechanism. To reconstruct the reaction kinematic and to identify the useful reaction mechanism, the energy and angle of at least two of the three outgoing particles must be carefully measured. Moreover, enough statistics is required, as the quasi-free events usually represent just a small fraction of the acquired statistic. These requirements hardly match with the typical characteristics of radioactive ion beams: low intensity, large divergence and possible presence of contaminants. For this reason, only recently the Trojan Horse Method has been applied to study reactions induced by radioactive beams. This application gives also the opportunity to measure cross section of neutron induced reactions on radioactive isotopes, even if they have a short lifetime. In the following some results obtained in the study of the reactions 18F(p,α)15O and 18F(n,α)15N will be presented.
We discuss how the new measurement of the 12C + 12C fusion cross section carried out with the Trojan Horse Method affects the compactness of a star, i.e., basically the binding energy of the inner ...mantle, at the onset of the core collapse. In particular, we find that this new cross section significantly changes the dependence of the compactness on the initial mass with respect to previous findings obtained in Chieffi & Limongi by adopting the classical cross section provided by Caughlan & Fowler. A non-monotonic but well-defined behavior is also confirmed in this case and no scatter of the compactness around the main trend is found. Such an occurrence could impact the possible explodability of the stars.
For nucleosynthesis calculations, precise reaction rates should be known at energies within the Gamow window. At these energies, electron screening cannot be neglected. Despite the significance of ...the effect, a huge disagreement between experimental data and theoretical predictions is still not understood. In order to address to this problem, we investigated the dependence of the electron screening potential on the target host lattice structure by measuring the rate of the
2
H(
19
F,p)
20
F reaction in zirconium, titanium and palladium targets containing deuterium.
In this work we investigate fusion induced by a radioactive 8Li projectile on a 4He gas target, at center-of-mass energies between 0.6 and 5 MeV. The main result is the tendency of the dimensionless ...fusion cross section to form well visible plateaus alternated to steep rises. This is likely to be the most genuine consequence of the discrete nature of the intervening angular momenta observed so far in fusion reactions right above the Coulomb barrier. A partial-wave analysis, exclusively based on a pure quantal penetration fusion model, identifies a remarkably low-height barrier. Indeed, these plateaus allow enhanced experimental sensitivity to the fusion barrier given that the most barrier-sensitive lowest partial waves are well separated. We expect that the present results for 8Li+4He will promote further investigations of the fusion reaction mechanism between very light ions at energies much below the interaction barrier. For the moment, we believe that understanding the plateau origin in the cross section above the barrier will almost certainly be useful to corroborate the extrapolation to the important astrophysical region below the Coulomb barrier, not only in the case of the 8Li+4He fusion but also for other systems, such as the 12C+12C.
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 12
C
+12
C
fusion will be addressed.
The Extreme Light Infrastructure-Nuclear Physics (ELI-NP) facility, under construction in Magurele near Bucharest in Romania, will provide high-intensity and high-resolution gamma ray beams that can ...be used to address hotly debated problems in nuclear astrophysics, such as the accurate measurements of the cross sections of the 24Mg(γ,α)20Ne reaction, that is fundamental to determine the effective rate of 28Si destruction right before the core collapse and the subsequent supernova explosion. For this purpose, a silicon strip detector array (named ELISSA, acronym for Extreme Light Infrastructure Silicon Strip Array) will be realized in a common effort by ELI-NP and Laboratori Nazionali del Sud (INFN-LNS), in order to measure excitation functions and angular distributions over a wide energy and angular range. A prototype of ELISSA was built and tested at INFN-LNS in Catania (Italy) with the support of ELI-NP. In this occasion, we have carried out experiments with alpha sources and with a 11 MeV 7Li beam. Thanks to our approach, the first results of those tests show up a very good energy resolution (better than 1%) and very good position resolution, of the order of 1 mm. Moreover, a threshold of 150 keV can be easily achieved with no cooling.
The Trojan Horse Method in Nuclear Astrophysics Tumino, Aurora; Spitaleri, Claudio; Cherubini, Silvio ...
EPJ Web of Conferences,
01/2018, Letnik:
184
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
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.
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