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Physical Review Letters 101 (2008) 212503
Decay Pattern of Pygmy States Observed in Neutron-Rich 26Ne
J. Gibelin1, D. Beaumel1, T. Motobayashi, Y. Blumenfeld1, N. Aoi, H. Baba, Z. Elekes, S. Fortier1, N. Frascaria1, N. Fukuda, T. Gomi, K. Ishikawa, Y. Kondo, T. Kubo, V. Lima1, T. Nakamura, A. Saito, Y. Satou, J. A. Scarpaci1, E. Takeshita, S. Takeuchi, T. Teranishi, Y. Togano, A. M. Vinodkumar, Y. Yanagisawa, K. Yoshida

Coulomb excitation of the exotic neutron-rich nucleus 26Ne on a 208Pb target was measured at 58  MeV/u in order to search for low-lying E1 strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of B(E1)=0.49±0.16e2  fm2 is deduced, corresponding to 4.9±1.6% of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay
Physique/Physique Nucléaire Expérimentale