2α+t cluster structure in 11B

The cluster structures of the excited states in 11B are studied by analyzing the isoscalar monopole and quadrupole strengths in the B11(d,d′) reaction at Ed=200MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. The large monopole strength for the 3/23− state at Ex=8.56MeV is well described by the AMD calculation and is suggested to be an evidence for a well developed 2α+t cluster structure.