Two-body mechanisms in light-ion reactions with $^9$Be

Abstract

Few-nucleon transfer reactions induced by light projectiles ($d$, ${}^{3}\text{He}$, and ${}^{4}\text{He}$) on the weakly bound nucleus ${}^{9}\text{Be}$ were investigated at incident energies of 26--35~MeV. Inclusive energy spectra and angular distributions were measured for outgoing fragments ($p$, $d$, $t$, ${}^{4}\text{He}$, ${}^{7}\text{Li}$, and ${}^{7}\text{Be}$), allowing reconstruction of excitation energy spectra for the complementary residual nuclei. The observed spectral shapes are consistent with discrete level populations in both bound and unbound systems, supporting a dominant two-body reaction mechanism.

Special attention was given to channels involving short-lived unbound nuclei (${^{5}\text{He}}$, ${^{5}\text{Li}}$, and ${^{8}\text{Be}}$). The extracted energy peaks and widths indicate population of these systems predominantly in their ground states. Comparisons with phase-space models and kinematic simulations exclude a statistical three-body decay scenario and confirm the formation of binary final states.

A time-scale analysis based on resonance widths yields equilibration times shorter than $10^{-22}$~s, suggesting that energy sharing occurs rapidly in these reactions. These findings support a cluster-transfer picture in which preformed configurations, such as ${}^{5}\text{He}$ and $\alpha$ clusters, are coherently transferred. The results provide new constraints on reaction dynamics and cluster structure in light nuclei.