Breaking of N=8 magicity in 13Be

Abstract

Structure of ${}^{13}$Be was investigated with antisymmetrized molecular dynamics. The variation after spin and parity projections was performed. An unnatural parity $1/2^{-}$ state was suggested to be lower than $5/2^{+}$ state indicating that vanishing of the N=8 magic number occurs in ${}^{13}$Be. A low-lying $3/2^{+}$ state with a $2\hslash \omega$ configuration was also suggested. Developed cluster structures were found in the intruder states. Lowering mechanism of the intruder states was discussed in terms of molecular orbitals around a $2\alpha$ core.

Comments: 9 pages, 8 figures, submitted to PRC