Excited states of 11Be

The 11B(7Li,7Be)11Be reaction at 57 MeV incident energy was studied at forward angles in order to explore the 11Be excitation energy spectrum. The 11Be ground state and the states at E∗=0.32,1.77,2.67,3.41,3.89,3.96,6.05 MeV excitation energies were populated. The state at 6.05 MeV (FWHM 320±40 keV) has not been previously observed. The good energy resolution (∼50 keV) allowed the identification of these transitions each for 7Be in its ground and first excited state at E∗=0.429 MeV. QRPA calculations reproduce the 11Be level structure below 2 MeV of excitation energy. The strength observed at higher excitation energies is very likely produced mainly by core-excited components of 11Be.