Valdir Guimaraes

The optical model (OM) formalism inherently omits the structural properties of weakly bound nuclei, owing to its restriction to an effective two-body description. By assuming the halo and non-halo configurations of 8B and 11Be projectiles on two quite different mass targets, 64Zn and 208Pb, we introduce an approach that explicitly incorporates the ground-state structure of a weakly bound projectile by embedding its wave function into the projectile-target nuclear potential through a double-folding formalism. The resulting potential successfully reproduces the suppression of the Coulomb-nuclear interference peak observed in elastic scattering, which is commonly attributed to coupling with breakup channels. Moreover, incorporating the halo structure into the OM significantly improves the agreement with experimental elastic-scattering data. These results for weakly bound nuclei demonstrate that an accurate description of elastic scattering requires an OM that explicitly accounts for the projectile's structure.

We present the first direct measurement of the Z=6 shell gap in the neutron-rich ^{20}O nucleus. The one-proton removal transfer reaction ^{2}H(^{20}O,^{3}He)^{19}N has been studied using the ACTAR TPC setup at GANIL. The use of ACTAR TPC enabled the measurement of low-cross section proton-removal reactions while preserving resolution. Eight p-hole states with ℓ=1 were identified in ^{19}N accounting for total strengths of 86% and 72% of the 0p_{3/2} and 0p_{1/2} single-particle orbitals, respectively. The energies and spectroscopic factors of the measured states allowed to determine the proton spin-orbit splitting π0p_{3/2}-π0p_{1/2} in ^{20}O. The Z=6 shell gap has been established to be 5.30(14) MeV. These findings indicate a reduction of the Z=6 shell gap while adding neutrons to the sd-valence orbitals, consistent with the effects of the tensor force predicted by state-of-the-art shell model interaction SFO-tls while at variance with the emergence of a large Z=6 gap observed in other studies.

Introduction: A phenomenological analysis, based on distances, has been performed for elastic scattering data induced by tightly bound (¹¹B, ¹²C, and ¹⁶O), weakly bound (⁶Li, ⁷Li, ⁷Be, and ⁹Be), and exotic (⁶He, ⁸B, ¹¹Be, and ¹⁵C) nuclei on light (²⁷Al), medium (⁵⁸Ni and ¹²⁰Sn), and heavy mass (²⁰⁸Pb) targets, respectively, at energies close to the Coulomb barrier.Methods: The cross-section data on the angular distributions have been converted as a function of the distance of the closest approach.Results: From a fitting analysis, critical interaction and strong absorption distances were extracted from the data.Discussion: Correlation was observed with the projectile cluster configuration for the data on the target ²⁰⁸Pb.

Editorial: Clustering in light nuclei: current research, new aspects, challenges and perspectives

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of ²⁶Al and ²²Na. While γ rays from the decay of the former radioisotope have been observed throughout the Galaxy, ²²Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The ²²Na(p, γ)²³Mg reaction remains the only source of large uncertainty about the amount of ²²Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in ²³Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the ²³Mg states, places strong limits on the amount of ²²Na produced in novae and constrains its detectability with future space-borne observatories.

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of ²⁶Al and ²²Na^1-3. While γ rays from the decay of the former radioisotope have been observed through-out the Galaxy, ²²Na remains untraceable. The half-life of ²²Na (2.6 yr⁴) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus⁵. The ²²Na(p, γ)²³Mg⁵ reaction remains the only source of large uncertainty about the amount of ²²Na ejected. Its rate is dominated by a single reso- nance on the short-lived state at 7785.0(7) keV in ²³Mg⁶. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the ²³Mg states, combining magnetic and highly-segmented tracking γ-ray spectrometers, places strong limits on the amount of ²²Na produced in novae, explains its non-observation to date in γ rays (flux < 2.5×10⁻⁴ ph.cm⁻²s^{−1 7}), and constrains its detectability with future space-borne observatories.