Direct probing of the cluster structure in Be 12 via the α -knockout reaction

Background: Recent theoretical and experimental researches using proton-induced α-knockout reactions provide direct manifestation of α-cluster formation in nuclei. In recent and future experiments, α-knockout data are available for neutron-rich beryllium isotopes. In Be12, rich phenomena are induced by the formation of α clusters surrounded by neutrons; for instance, breaking of the neutron magic number N=8. Purpose: Our objective is to provide direct probing of the α-cluster formation in the Be12 target through associating the structure information obtained by a microscopic theory with the experimental observables of α-knockout reactions. Method: We formulate a new wave function of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) type for the structure calculation of Be12 nucleus and integrate it with the distorted-wave impulse-approximation framework for the α-knockout reaction calculation of Be12(p,pα)He8. Results: We reproduce the low-lying spectrum of the Be12 nucleus by using the THSR wave function and discuss the cluster structure of the ground state. Based on the microscopic wave function, the optical potentials and α-cluster wave function are determined and utilized in the calculation of Be12(p,pα)He8 reaction at 250 MeV. The possibility of probing the clustering state of Be12 through this reaction is demonstrated by analysis of the triple differential cross sections that depend sensitively on the α-cluster amplitude at the nuclear surface. Conclusions: This study provides a feasible approach to validate directly the theoretical predictions of clustering features in the Be12 nucleus through the α-knockout reaction.