SHAPE COEXISTENCE IN SM-138 AND EVIDENCE FOR THE ROTATIONAL ALIGNMENTOF A PAIR OF N=6 NEUTRONS

The level scheme of Sm-138 has been extended up to I-pi = (32(+)) usin g gamma-ray coincidence data collected with the Eurogam array. The Cd- 106(Cl-35,3p)Sm-138 fusion-evaporation reaction was used at a bombardi ng energy of 150 MeV. Several new bands have been observed and the kno wn bands extended to higher spin. Band crossings and shape coexistence are discussed with the aid of Woods-Saxon cranking calculations (CMS and TRS). Evidence is presented for a neutron [i(13/2)](2) pair alignm ent which is predicted to drive the nucleus to a prolate shape with en hanced quadrupole deformation beta(2) = 0.32. A strongly coupled band was also established and is interpreted as a collectively rotating obl ate structure.