Background: Heavy-ion fusion cross-sections at sub barrier energies are found to be enhanced by orders of magnitude as compared to the predictions of one-dimensional barrier penetration model (1-D BPM). The coupling of various internal degrees of freedom has been employed to decrypt the mechanism responsible for the observed sub-barrier fusion enhancement. However, the unambiguous role of multi-neutron transfer channels in the sub-barrier domain is still elusive.

The phenomenon of enhanced fusion cross-section as compared to the theoretical predictions of 1-D BPM has been extensively studied over the past few decades. However, the unambiguous role of neutron transfer channels on the sub-barrier fusion enhancement is still elusive in most cases. Fusion cross-section measurements ≈ 15% below and above the Coulomb barrier were performed to elucidate the mechanisms responsible for the experimentally observed sub-barrier fusion enhancement. Coupled-channels calculations using CCFULL were used to decipher the reaction dynamics. CC calculations explained the fusion excitation function for ²⁸Si + ^116,120Sn systems after the inclusion of inelastic excitations along with a pair transfer. However, the observed behavior for the ²⁸Si + ¹²⁴Sn system could not be explained. The fusion barrier distribution has been extracted from the experimental data to unveil the various channels coupled in the concerned rection. A single uncoupled barrier was transformed into a distribution of barriers depicting the presence of different channels coupled in the reaction. The results indicate a significant effect from multi-neutron transfer channels on the fusion dynamics.

This work explores the possibility of using 4H-SiC PIN diodes to provide a high electric field able to induce the Stark effect in ⁷Be atoms implanted in the diode space charge region, modifying the ⁷Be radioactive decay time. A set of PIN diodes of area ranging between 2.12 × 10⁻³ cm² and 9.88 × 10⁻³ cm² was designed and fabricated to reach breakdown voltages up to 1000 V. Be ions were implanted in the epitaxial layer, and then the devices were reverse biased at about 75% of the theoretical breakdown voltage for durations exceeding 100 days, long enough for a precise measurement of the ⁷Be radioactive decay time. Electrical characterization in the pristine state, after Be ion implantation, and after long reverse bias allowed us to verify the suitability of 4H-SiC PIN diodes by assessing both the agreement between simulated and measured performance and the stability of the electric field. Be ion implantation-related defects induced both an increase in the reverse current generation and a decrease in the junction capacitance, though not affecting the breakdown voltage. Comparison with test devices implanted with the stable isotope ⁹Be indicates that any defects introduced by the ⁷Be radioactive decay are below the detection limit of the employed characterization techniques and have a negligible impact on the reverse-blocking characteristics of the diodes. Device simulations allowed us to conclude that the electric field remains close to its theoretical value throughout the experiment duration, confirming the suitability of 4H-SiC diodes for both induction and measurement of ⁷Be lifetime variations.

Context. Carbon burning determines the destiny of stars with masses higher than ≈8 M _⊙ and mass-accreting white dwarfs (WDs) in close binary systems. For this reason, in order to understand several astrophysical phenomena it is necessary to understand this key evolutionary phase; examples include determining the mass limits of CO and ONe WDs, the rates of e-capture, core-collapse, and Type Ia supernovae, and the contribution of massive stars to the chemical evolution. Despite its fundamental importance in astrophysics, the rate of the leading fusion process – the ¹² C+ ¹² C reaction – remains largely uncertain at relevant stellar temperatures. Aims. Revision of the ¹² C+ ¹² C reaction rate of both the α and the p channels and evaluation of the consequent impact on star models of mass ranging between 8 and 20 M _⊙ . Methods. Based on the latest direct measurements of the ¹² C+ ¹² C cross section in the 2.8–4 MeV energy range, we calculated two new lower bounds for the rate of the ¹² C+ ¹² C process. These two estimates are obtained using different assumptions for the low-energy extrapolation of the modified astrophysical S ^* ( E ) factor: one replacing the method adopted by Caughlan & Fowler (1988, At. Data Nucl. Data Tables, 40, 283, CF88), and another based on a hindrance model. Results. The new rates are substantially lower than that commonly used in current stellar models of massive stars and accreting WDs. Specifically, the ratio between the new rate calculated in this work and the rate adopted in CF88 is, at T = 1 GK, 0.2 for the p channel and 0.085 for the α channel. Consequently, the characteristic carbon-burning temperatures and densities shift to higher values than those previously reported and the corresponding lifetime is significantly reduced. The maximum mass for progenitors’ pure CO WDs is higher as well as the maximum CO WD mass. Moreover, in a 20 M _⊙ model close to central Si depletion, the physical structure of the core is less dense in the region between 2 and 4 M _⊙ from the center. This fact should have important consequences for the resulting explosive properties.