Physics Letters B 541 (2002) 52–58 www.elsevier.com/locate/npe Low-lying dipole strength in 20O

Two 1 − levels at 5.35(10) and 6.85(5) MeV were observed for the first time in 20O. The strong direct excitation and subsequent γ-ray decay of these states in virtual photon scattering at 100 MeV/nucleon, along with B(Eλ) predictions for 20O states in this energy region, established their dipole character. The extracted B(E1) ↑ values of 0.062(16) e2 fm2 and 0.035(9) e2 fm2 for the 5.35 and 6.85 MeV states, respectively, are significantly larger than shell model calculations predict. Such large dipole strengths are not observed for low-lying 1 − states in 18O, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip-line. 2002 Elsevier Science B.V. All rights reserved