B(E1) strengths from Coulomb excitation of 11Be

The B(E1;1/2+→1/2−) strength for 11Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for Be11+Pb208 at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e2 fm2 derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e2 fm2. This value is in good agreement with the value deduced independently from the lifetime of the 1/2− state in 11Be, and has a comparable precision.