The Trojan Horse method (THM) is a well-established experimental technique to measure nuclear reactions of astrophysical interest avoiding the suppression of the Coulomb barrier affecting ...experimental direct measurements. In this paper it will describe some of the THM studies involving few-body system of interest for both nuclear physics and nuclear astrophysics, such as the sub-Coulomb proton-proton elastic scattering and the deuteron-deuteron fusion at energies of interest for primordial nucleosynthesis. Moreover, the role of the intercluster motion in nuclei used for THM measurement will be highlight for the discussed physics cases.
Astrophysics studies with the Trojan Horse Method Spitaleri, C.; La Cognata, M.; Lamia, L. ...
The European physical journal. A, Hadrons and nuclei,
09/2019, Letnik:
55, Številka:
9
Journal Article
Recenzirano
.
The Trojan Horse Method represents an indirect approach to investigate reactions of astrophysical relevance at the energies of interest, free of Coulomb suppression and electron screening effects. ...In this review, we will examine how the Trojan Horse Method has evolved from the study of the quasi-free reaction mechanism. We will first present the basic features of the quasi-free reaction mechanism in the framework of the theory of direct reactions, from quasi-free scattering to quasi-free reactions processes, and its evolution towards the Trojan Horse Method with its modern theory. We will review the validity tests to assess the technique, the procedure to analyze the data and to extract the astrophysical factor. Finally, we will discuss some of the most important experimental results recently published related to nuclear astrophysics and applications.
The Trojan Horse Method (THM) lays its foundations on the cluster structure of light nuclei which are usually used as “Trojan horses”. Many of them were successfully employed in the last decades to ...shed light to numerous astrophysical problems. Cluster structure and dynamics also suggest a series of tests which may be performed in order to strengthen the basis of the method. Among them pole invariance was investigated for three different situations. In fact, the cross sections for the
6
Li(d,
α
)
4
He,
2
H(d,p)
3
H and
7
Li(p,
α
)
4
He binary reactions were measured for several break-up schemes and analyzed within the framework of the Plane Wave Impulse Approximation (PWIA). The indirect results extracted by using different Trojan Horse nuclei (e.g.
2
H,
3
He,
6
Li) were compared with each other as well as with direct measurements of the corresponding astrophysical reactions. The very good agreement obtained confirms the applicability of the pole approximation and of the pole invariance method, namely the independence of binary indirect cross section on the chosen Trojan Horse nucleus, at least for the cases investigated. Moreover, we can verify that the effect of using a charged or a neutral particle as a spectator implies negligible corrections consistent with the experimental errors. In addition, the dynamics of clusters inside the Trojan Horse nucleus and their fingerprints on the measured momentum distribution play a key role for THM applications. In this article we will therefore discuss also these assertions studied in different systems(
2
H,
3
He,
6
Li,
9
Be,
14
N) and in particular for the deuteron case the relative impact of
s
and
d
waves in the momentum distribution will also be examined.
The study of energy production and nucleosynthesis in stars requires an increasingly precise knowledge of the nuclear reaction rates at the energies of interest. To overcome the experimental ...difficulties arising from the small cross sections at those energies and from the presence of the electron screening, the Trojan Horse Method has been introduced. The method provides a valid alternative path to measure unscreened low-energy cross sections of reactions between charged particles, and to retrieve information on the electron screening potential when ultra-low energy direct measurements are available.
The abundance of 26Al carries a special role in astrophysics, since it probes active nucleosynthesis in the Milky Way and constrains the Galactic core-collapse supernovae rate. It is estimated ...through the detection of the 1809 keV γ-line and from the superabundance of 26Mg in comparison with the most abundant Mg isotope (A = 24) in meteorites. For this reason, high precision is necessary also in the investigation of the stable 27Al and 24Mg isotopes. Moreover, these nuclei enter the so-called MgAl cycle, playing an important role in the production of Al and Mg. Recently, high-resolution stellar surveys have shown that the Mg–Al anticorrelation in red-giant stars in globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not be correlated with Al. The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show large uncertainties owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84 keV resonance and to lower upper limits on the strength of nearby resonances. In intermediate-mass AGB stars experiencing hot bottom burning, a sizeable increase in surface aluminum abundance is observed at the lowest masses, while 24Mg is essentially unaffected by the change in the reaction rate.
Abstract
A broad range of Nuclear Physics research activities have been carried out at INFN-LNS until the summer 2020, when the accelerators were stopped for the upgrade. The upgrade of LNS is a ...project mainly funded by a PON-FESR (National Program for Research and Innovation) strategic line for boosting the research infrastructures, having its own goals, time-schedule and deadlines. In addition to such an action promoted by the Italian Ministry of Research, further funds have been made available from INFN budget. The end of the phase supported by the PON for procurement and tenders is currently set for the end of 2023. A series of actions will therefore be implemented to improve scientific opportunities for users. In particular, the focus is on the commissioning of the Tandem and Superconducting Cyclotron with the new set-up, completed by the renewal of the experimental areas and the commissioning of the new fragment separator FRAISE, also financed under the PON. The high-intensity program, including the determination of the nuclear matrix elements (NME) for the double beta decay and the study of EOS for nuclear matter with large neutron content, will be made feasible by these improvements to accelerators, beamlines and detectors. Some highlights of the whole activity as well as of the Applied Physics perspectives and the Astroparticle Physics multi-messenger program, strictly connected to the Nuclear Physics program, are given.
•A new indirect measurement of the 27Al(p,α)24Mg has been carried out down to astrophysical energies.•The strength of the 84.3 keV resonance has been measured, and more stringent upper limits of ...nearby resonances have been set.•A new recommended reaction rate has been established, leading to a factor of 3 lower 27Al destruction rate.•Preliminary nucleosynthesis calculations have shown ∼30% changes in 27Al and 24Mg abundances for intermediate mass stars.
The 26Al abundance holds a special role in present-day astrophysics, since it is a probe of active nucleosynthesis in the Galaxy and a valuable constraint of Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809-keV γ-line of the daughter 26Mg and from the superabundance of 26Mg in comparison with the most abundant 24Mg isotope in meteorites. Accurate knowledge of the reaction rates involving 26Al, its stable counterpart 27Al and 24Mg is then mandatory. Moreover, these nuclei enter the MgAl cycle playing an important role in the production of Al and Mg isotopes. Recently, high-resolution stellar surveys have shown that the Mg-Al anti-correlation in red giants of globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not show correlation with Al.
The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show an order of magnitude uncertainty owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84-keV resonance and to lower the upper limits on the strength of nearby resonances, with potential important impact for astrophysics. In particular, modifications in the 27Al and 24Mg abundances up to ∼30% are predicted for intermediate mass stars.
7Be destruction channels are currently a matter of study because of their influence on the 7Li cosmological abundances. Here, we determine the cross section of the (n, ) reaction by using Trojan ...Horse experimental data for the 7Li(p, )4He reaction and correcting for Coulomb effects. The deduced 7Be(n, )4He data overlap with the Big Bang nucleosynthesis energies and the deduced reaction rate allows us to evaluate the corresponding cosmological implications.
Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars 1 (exceeding eight solar masses) and superbursts from accreting neutron ...stars2,3. It proceeds through the 12C + 12C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is, 12C(12C, α)20Ne and 12C(12C, p)23Na-at temperatures greater than 0.4 × 109 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections 4 for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks 4 below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate 5 at temperatures below 1.2 × 109 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the 12C(12C, α0,1)20Ne and 12C(12C, p0,1)23Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20Ne and 23Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method6,7 and the deuteron in 14N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 × 108 kelvin, the reaction rate is boosted to more than 25 times larger than the reference value 5 . This finding may have implications such as lowering the temperatures and densities 8 required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models 3 .
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