Excited states of Be-11

The B-11(Li-7,Be-7)Be-11 reaction at 57 MeV incident energy was studied at forward angles in order to explore the Be-11 excitation energy spectrum. The Be-11 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 (similar to 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 Be-11 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 Be-11. (C) 2001 Published by Elsevier Science B.V.