Abstract
Coulomb excitation of the exotic neutron-rich nucleus on a target was measured at in order to search for low-lying 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 channel, we observe a sizable amount of strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of is deduced, corresponding to 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.
- Received 7 March 2008
DOI:https://doi.org/10.1103/PhysRevLett.101.212503
©2008 American Physical Society