We investigate to what extent a description of ${}^{12}\mathrm{Be}$ as a three-body system made of an inert ${}^{10}\mathrm{Be}$ core and two neutrons is able to reproduce the experimental ${}^{12}\mathrm{Be}$ data. Three-body wave functions are obtained with the hyperspherical adiabatic expansion method. We study the discrete spectrum of ${}^{12}\mathrm{Be}$, the structure of the different states, the predominant transition strengths, and the continuum energy spectrum after high-energy fragmentation on a light target. Two $0^{+}$, one $2^{+}$, one $1^{-}$, and one $0^{-}$ bound states are found; the first four are known experimentally, whereas the $0^{-}$ is predicted as an isomeric state. An effective neutron charge, reproducing the measured $B(E1)$ transition and the charge rms radius in ${}^{11}\mathrm{Be}$, leads to a computed $B(E1)$ transition strength for ${}^{12}\mathrm{Be}$ in agreement with the experimental value. For the $E0$ and $E2$ transitions, the contributions from core excitations could be more significant. The experimental ${}^{10}\mathrm{Be}$-neutron continuum energy spectrum is also well reproduced, except in the energy region corresponding to the $3/2^{-}$ resonance in ${}^{11}\mathrm{Be}$ where core excitations contribute.

• Received 5 December 2007

DOI:https://doi.org/10.1103/PhysRevC.77.054313