The strength distributions of Gamow-Teller (GT) transitions from ${}^{11}\mathrm{Li}$ and ${}^{12}\mathrm{Be}$ are investigated. We study where the GT strengths of the transitions ${}^{11}\mathrm{Li}$ ${(3/2\mathrm{}}_{\mathrm{gs}}^{\mathrm{-}}{)\to }^{11}{\mathrm{Be}}^{*}$ (${1/2}^{-},$ ${3/2}^{-},$ ${5/2}^{-}$) are located incorporating quenching effects due to the Δ-hole contributions. The connection between the GT sum rule and effects of the halo structure of ${}^{11}\mathrm{Li}$ are discussed. The narrowing of the gap between the $p$ shell and the $\mathrm{sd}$ shell is found to change the structure of the GT strength distribution. The accuracy of the present calculation is tested for the GT decay from ${}^9\mathrm{Li}.$ We further study the GT transition from ${}^{12}\mathrm{Be}.$ The narrowing of the gap between the $p$ and $\mathrm{sd}$ shells varies the transition strength to ${}^{12}\mathrm{Be}$ ${(1\mathrm{}}_{\mathrm{gs}}^{+})$ as well as the GT distribution. The quenching of the transition strength ${}^{12}{\mathrm{Be}\to }^{12}\mathrm{B}$ ${(1\mathrm{}}_{\mathrm{gs}}^{+})$ suggests an enormous breaking of the neutron closed-shell structure of ${}^{12}\mathrm{Be}.$

• Received 9 December 1996

DOI:https://doi.org/10.1103/PhysRevC.56.847