Direct probing of the cluster structure in 12Be 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 ¹²Be, 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 ¹²Be 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 ¹²Be nucleus and integrate it with the distorted-wave impulse-approximation framework for the α -knockout reaction calculation of ¹²Be(p ,p α )⁸He .

Results: We reproduce the low-lying spectrum of the ¹²Be 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 ¹²Be(p ,p α )⁸He reaction at 250 MeV. The possibility of probing the clustering state of ¹²Be 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 ¹²Be nucleus through the α -knockout reaction.