Abstract
The energies of the excited states in very neutron-rich and have been measured using in-beam -ray spectroscopy from the fragmentation of secondary beams of at . The low energy of , 770(19) keV, together with the level schemes of , provides evidence for the disappearance of the and spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that is best described as a well-deformed oblate rotor.
- Received 20 December 2006
DOI:https://doi.org/10.1103/PhysRevLett.99.022503
©2007 American Physical Society