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The Mg–Al cycle is characteristic of the high-temperature (T ∼ 0.055 GK) H-burning of evolved stars and their nucleosynthesis. A proper comprehension of this reaction network can help in solving debated questions such as the occurrence of anticorrelation in Mg–Al abundances in globular clusters. Recent high-resolution surveys have shown that such an anticorrelation may hide the existence of multiple stellar populations and that the relative abundances of Mg isotopes may not be correlated with Al. Proton-induced reactions on 27Al play a key role in this respect, in particular the interplay between the (p, α) and (p, γ) channels, determining the closure (or not) of the Mg–Al cycle. Presently, the situation is still debated owing to the large uncertainty affecting existing experimental nuclear data. A recent indirect measurement indicates a further reduction in the 27Al(p, α)24Mg reaction rate with respect to the ones commonly adopted in astrophysical models. In the present work, we update the 27Al(p,γ)28Si reaction rate based on the same indirect measurement results. In the case of AGB stars experiencing hot bottom burning, the revised rate would lead to a ∼35% increase in 27Al abundance with respect to what is presently foreseen, with interesting astrophysical consequences.

Indirect methods have proven to be a complementary approach for extending our knowledge of nuclear structure and low-energy cross sections. Among these, the neutron-induced reaction cross sections appear to be of particular interest since their role both for unstable and stable beams. In view of this, we report here the combined study of the 17O(n, α)14C reaction accomplished by the Trojan Horse Method (THM) and the asymptotic normalization coefficient (ANC) method. The low-lying 8038, 8125, 8213, and 8282 keV resonances in 18O are studied, and their Γ n are derived. A comparison with recent direct data and recent THM experimental data is presented. The independent ANC investigation corroborates our previous THM results, confirms the consistence of the two indirect investigations, and shows new frontiers for neutron-induced reactions with radioactive ion beams. Moreover, we examined the impact of adopting the newly recommended 17O(n, α)14C reaction rate on asymptotic giant branch stars' nucleosynthesis. Our findings reveal significant variations (≳10%) in the production of the neutron-rich heavy isotopes sensitive to neutron density, underlining the neutron-poisoning effect of 17O on the s-process.

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 neutron capture reaction 10 B(n, α ) 7 Li has been investigated via the Trojan Horse Method from 0 to 1 MeV. The α 0 and α 1 channels, corresponding to 7 Li in its g.s. and 1st excited level respectively, have been analyzed and cross sections have been measured for the two reaction channels. Angular distributions for the 11 B energy levels in the explored range have been extracted and compared with literature, while the J π of the level at E 11 B = 11.450 MeV (4 keV before the α emission threshold) has been clearly determined for the first time.

. In the framework of the experimental campaign of the ( p , α ) and ( n , α ) reactions cross sections measurement involving the 10, 11 B isotopes, different ( n , α ) cross section measurements have been performed at ultra-low energy. In this work, the 10 B( n , α ) 7 Li reaction was investigated through the Trojan Horse Method, by means of the Quasi-Free (QF) 2 H( 10 B, α 7 Li) 1 H reaction at 30 MeV of beam energy. As in the standard THM approach, the measurement has been performed in inverse kinematics using a 10 B beam. The excitation function of the 10 B( n , α ) 7 Li reaction has been measured at a center-of-mass energy between 0 and 700 keV. The data were compared with the existing experimental ones. Even if the energy resolution of the present experiment did not allow a separation between the channels ( n , α 0 ) and ( n , α 1 ) the low energy cross section and the angular distribution are presented, pointing out once more the ability of the method in studying neutron induced reactions using deuteron as source of virtual neutrons.

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 stars 2 , 3 . It proceeds through the 12 C +  12 C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23—that is, 12 C( 12 C, α) 20 Ne and 12 C( 12 C, p ) 23 Na—at temperatures greater than 0.4 × 10 9 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 × 10 9 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the 12 C( 12 C, α 0,1 ) 20 Ne and 12 C( 12 C, p 0,1 ) 23 Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20 Ne and 23 Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method 6 , 7 and the deuteron in 14 N. 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 × 10 8 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 . The rate of carbon burning— 12 C +  12 C fusion—in stars is boosted by resonant behaviour at astrophysical energies.

In equation (1) of this Letter, the closing bracket was missing; in Extended Data Fig. 1 and the accompanying legend, ‘ Φ ( p d )’ should have been ‘ Φ 2 ( p d )’, and in the Methods the text “Odd J assignments are uncertain by ±1.” has been added. These errors have all been corrected online.

. The 10 B(p, α 1 ) 7 Be reaction has been studied for the first time via the Trojan Horse Method (THM) applied to the 2 H( 10 B, α 7 Be)n quasi-free three-body process. The present experiment allowed for a clear separation between α 0 and α 1 channels thanks to the improved energy resolution with respect to previous THM studies of the 2 H( 10 B, α 7 Be)n reaction. The extracted half-off-energy-shell cross section was found to be characterized by several structures attributable to the population of 11 C. In particular, six resonances have been observed at 10.086, 10.352, 10.525, 10.686, 10.841 and 10.976 MeV 11 C excitation energy.

The p - p-chain reaction 3He(α, γ)7Be can sensitively influence the prediction of the 7Be and 8B neutrino fluxes. Despite its importance, the knowledge of its reaction cross section at energies of the core of the Sun (15 keV 30 keV) is limited and the accuracy far from the desired 3% level. In the present paper the indirect measurement of the external capture contribution using the asymptotic normalization coefficient (ANC) technique is reported. The angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reactions were measured and the ANCs extracted from the scaling of distorted-wave Born approximation (DWBA) and coupled-channel (CC) calculations. Then, the astrophysical S-factor for the 3He(α, γ)7Be reaction was calculated assuming E1 direct capture and the zero energy value turned out to be 0.534 0.025 keVb. Both our experimental and theoretical approaches were benchmarked through the analysis of the 6Li(p,γ)7Be astrophysical factor, with interesting astrophysical applications to the understanding of the primordial lithium problem. In particular, the present work disfavors the occurrence of a claimed 200 keV resonance in the astrophysical factor.